In relation to its tolerance to shadow, lenga has been classified as either "purely heliophilous" (Mutarelli & Orfila, 1971), "semi-heliophilous" (Tortorelli, 2009), "medium tolerant" (Rusch, 1992) to "semi-tolerant" (Donoso Z., 1987). These controversial or even opposite classifications are probably due to the different habitats these descriptions came from. It has been well established that for many species, proper development may depend on the limiting resources a given environment may have (Choler et al., 2001) so the radiating needs of lenga regeneration may significantly vary depending on a set of other

In sites with high rainfall levels (i.e. South of Tierra del Fuego and West of Chubut province), lenga regeneration is established even after major disturbances affecting up to hundreds or even thousands of hectares (Rebertus et al., 1997, Veblen et al., 1996). The same occurs in forests affected by intensive forest harvesting (Gea Izquierdo et al., 2004, Mutarelli & Orfila, 1971, Rebertus & Veblen, 1993, Rosenfeld et al., 2006). By contrast, in sites with water deficit during the summer, as in the northern sector of lenga distribution in Río Negro, Neuquén and Chubut provinces, regeneration cannot be established with low canopy coverage (Bava & Puig, 1992). In these areas, regeneration establishment is strongly influenced by water availability and usually occurs in small gaps caused by falling trees

Recent studies have analyzed the effects of micro-environmental factors on the establishment and growth of lenga seedlings in natural gaps. These studies showed that in the driest sites of lenga distribution, the shade generated by individuals from the edge of the gaps and the presence of coarse woody debris, produce a facilitator effect on seedling establishment (Heinemann & Kitzberger, 2006, Heinemann et al., 2000). Seedling survival in these xeric sites have been positively related to water availability, while in mesic sites survival seems to be controlled by both water availability and light (Heinemann &

**2. History of productive use of** *N. pumilio* **forests in Argentinean Patagonia**  Most of lenga productive forests in Argentinean Patagonia, owned by either private or state sectors, started to be exploited at the beginning of the XXth century, but did not reach significant levels of harvest until mid-century, with the emergence of large sawmills that used almost exclusively high quality timber. Since then, the closing down of these large sawmills and the gradual installation of small and medium sawmills generated changes in harvesting techniques, extraction rates, and final products. These changes were usually marked by the lack of effective control policies by the state administration, which lead to the absence of sustainable management practices. Furthermore and to worsen this situation, these forests have been traditionally used as summer pastures for cattle, which in many cases has caused the degradation of the understory, with long delays in, and even

steppe, precipitation sharply diminishes to ca 500 mm annually (Barros et al., 1983, Jobbágy et al., 1995, Veblen et al., 1977). To the South of the 52 and up to the 55 º S parallel in the island of Tierra del Fuego, a regular rainfall pattern occurs, with rainfall evenly distributed throughout the year (Burgos, 1985);

Fig. 1. Distribution of *N. pumilio* forests (green shading) in Argentinean Patagonia.

#### **1.2 Disturbance regime**

Throughout its wide distribution area, lenga stands are clearly distinguishable from other component of the Andean forests, being composed of simple monospecific structures with narrow ecotones (Donoso Z., 1995). However, given the different environments in which it develops, lenga presents different structures and regenerative dynamics, mainly associated with the frequency, magnitude and severity of disturbances such as windstorms, fires, avalanches, landslides, or the falling of senescent trees (Donoso Z., 1995, Veblen et al., 1996). As a consequence of these disturbances, lenga stands may present either even or unevenaged structures, both situations representing extremes in a range of different possible structures. At the southern end of lenga distribution in Tierra del Fuego, tree falls usually occur due to wind storms, and this result in even-aged young structures (Rebertus et al., 1997). Furthermore, the same wind storms that cause large falls may also lead to formation

steppe, precipitation sharply diminishes to ca 500 mm annually (Barros et al., 1983, Jobbágy et al., 1995, Veblen et al., 1977). To the South of the 52 and up to the 55 º S parallel in the island of Tierra del Fuego, a regular rainfall pattern occurs, with rainfall evenly distributed

Fig. 1. Distribution of *N. pumilio* forests (green shading) in Argentinean Patagonia.

Throughout its wide distribution area, lenga stands are clearly distinguishable from other component of the Andean forests, being composed of simple monospecific structures with narrow ecotones (Donoso Z., 1995). However, given the different environments in which it develops, lenga presents different structures and regenerative dynamics, mainly associated with the frequency, magnitude and severity of disturbances such as windstorms, fires, avalanches, landslides, or the falling of senescent trees (Donoso Z., 1995, Veblen et al., 1996). As a consequence of these disturbances, lenga stands may present either even or unevenaged structures, both situations representing extremes in a range of different possible structures. At the southern end of lenga distribution in Tierra del Fuego, tree falls usually occur due to wind storms, and this result in even-aged young structures (Rebertus et al., 1997). Furthermore, the same wind storms that cause large falls may also lead to formation

throughout the year (Burgos, 1985);

**1.2 Disturbance regime**

of small gaps in the forest canopy. Uneven-aged structures are usually originated in mature forests located in favorable sites at low altitudes having low frequencies of catastrophic disturbances or human interventions. In these areas, the falling out of senescent trees may promote the opening of gaps or patches of about 0.1 ha (Bava, 1999, Veblen & Donoso Z., 1987) in which regeneration begins. These patches generally possess favorable undergrowth conditions which allow the formation of small clumps of saplings. The result of this process is a multi-aged and multi-strata forest, even when the formation of these gaps may be an episodic phenomenon (Rebertus & Veblen, 1993).

In relation to its tolerance to shadow, lenga has been classified as either "purely heliophilous" (Mutarelli & Orfila, 1971), "semi-heliophilous" (Tortorelli, 2009), "medium tolerant" (Rusch, 1992) to "semi-tolerant" (Donoso Z., 1987). These controversial or even opposite classifications are probably due to the different habitats these descriptions came from. It has been well established that for many species, proper development may depend on the limiting resources a given environment may have (Choler et al., 2001) so the radiating needs of lenga regeneration may significantly vary depending on a set of other environmental factors (Rusch, 1992).

In sites with high rainfall levels (i.e. South of Tierra del Fuego and West of Chubut province), lenga regeneration is established even after major disturbances affecting up to hundreds or even thousands of hectares (Rebertus et al., 1997, Veblen et al., 1996). The same occurs in forests affected by intensive forest harvesting (Gea Izquierdo et al., 2004, Mutarelli & Orfila, 1971, Rebertus & Veblen, 1993, Rosenfeld et al., 2006). By contrast, in sites with water deficit during the summer, as in the northern sector of lenga distribution in Río Negro, Neuquén and Chubut provinces, regeneration cannot be established with low canopy coverage (Bava & Puig, 1992). In these areas, regeneration establishment is strongly influenced by water availability and usually occurs in small gaps caused by falling trees (Rusch, 1992).

Recent studies have analyzed the effects of micro-environmental factors on the establishment and growth of lenga seedlings in natural gaps. These studies showed that in the driest sites of lenga distribution, the shade generated by individuals from the edge of the gaps and the presence of coarse woody debris, produce a facilitator effect on seedling establishment (Heinemann & Kitzberger, 2006, Heinemann et al., 2000). Seedling survival in these xeric sites have been positively related to water availability, while in mesic sites survival seems to be controlled by both water availability and light (Heinemann & Kitzberger, 2006, Heinemann et al., 2000).

#### **2. History of productive use of** *N. pumilio* **forests in Argentinean Patagonia**

Most of lenga productive forests in Argentinean Patagonia, owned by either private or state sectors, started to be exploited at the beginning of the XXth century, but did not reach significant levels of harvest until mid-century, with the emergence of large sawmills that used almost exclusively high quality timber. Since then, the closing down of these large sawmills and the gradual installation of small and medium sawmills generated changes in harvesting techniques, extraction rates, and final products. These changes were usually marked by the lack of effective control policies by the state administration, which lead to the absence of sustainable management practices. Furthermore and to worsen this situation, these forests have been traditionally used as summer pastures for cattle, which in many cases has caused the degradation of the understory, with long delays in, and even preclusion of, regenerative processes.

Sustainable Management of Lenga

"floreo" (high grading).

**2.3 Forest management plans**

of the Patagonian provinces.

Pastur et al., 2009).

**2.4 Cattle**

**2.2 The beginnings of industrial use: High grading**

and being controlled at different levels of implementation.

(*Nothofagus pumilio*) Forests Through Group Selection System 49

The first forest industries installed in the early twentieth century, either for medium or small sawmills, or for wood veneer production, were characterized by softly logging, cutting only healthy, medium-sized trees. Stem rots, caused mostly by fungi of the genera *Postia* and *Piptoporus*, is a very common phenomenon that affects lenga trees, being very important in old age trees. This determined that in virgin forests, only a small proportion of trees contained good quality timber. For that reason and in general, forest workers used to cut down only trees in good health status, medium-sized (40 - 50 cm DBH), which generally did not exceed 10% of forest trees in a stand. This type of "soft logging" was locally known as

The first Argentine Forest Law was put in force in 1948. While the concept of forest management, as a synonym of timber production, was prevalent in that law, it included articles about protection of soil, water and biodiversity. Although it mandated for the implementation of Forest management plans, its principles and regulations were applied sparingly. As a result, logging continued in public forests in an unplanned way. In the mid 50´s of the XXth century, the first forest management plans were designed and applied by Croat forest engineers, who arrived to Argentina after the World War II. These plans represented a breakthrough for the understanding of lenga forests, but had little practical effects on forest management due to the weaknesses of the Administrative forestry services

By the 80's, the practice of giving access to cut lumber in public or private forests depended on the approval of forest management plans by the provincial forest service, practice that became usual. However, these were just cutting plans, without long term planning horizon

Silvicultural aspects were changing over time with the evolution of knowledge about forests dynamics, from the early experiences on shelterwood systems in Chile (Cruz M. & Schmidt, 2007), clear-cut in Argentina (Mutarelli & Orfila, 1971), to the currently used alternatives, ranging from a group selection system (Bava & López Bernal, 2005) up to a variation of shelterwood systems with dispersal and-or aggregate retention (Martínez

As already mentioned, the first activity developed in Patagonian was sheep ranching. Near the Andes, the usual ranching scheme was a system that alternated winter grazing (locally called invernadas) in low areas with summer grazing areas at higher altitudes in the forest (called veranadas). There are plenty of examples of this system in mountain areas around the world. In the mid-twentieth century, with increasing population established in the area,

In lenga forest ecosystems of Patagonia, herbivory causes severe impacts, because this species is palatable to both wild (camelidae, deer and leporidae), and domestic livestock, and heavy grazing can prevent forest regeneration (Veblen et al., 1996). In Argentina, lenga forests suitable for timber production are mainly concentrated in the provinces of Chubut and Tierra del Fuego. Lenga forests in the province of Chubut are also a very important part of traditional cattle management, which similarly to what formerly occurred with sheep, alternates winter fields in the steppe with summer fields at the mountains (York et al., 2004).

cattle raising was becoming important, with the same production scheme.

The objective of this chapter was to analyze the evolution of productive schemes of lenga forests along their history of use, which will help us understand the overlap of strains on this resource, impacts on their conservation status, and the difficulties that currently have the implementation of sustainable management systems. For this purpose, we got information derived from published analyses, statistical records of the Forest Administration, analyses of historical harvesting, and of the impacts of livestock on forest regeneration. This information is presented for two contrasting situations, located one in the northern lenga distribution area in Chubut province and the other in its southern distribution area in Tierra del Fuego.

#### **2.1 Pre-industrial**

The original inhabitants of continental Patagonia were mostly nomadic Indian tribes that depended largely on the guanaco (*Lama guanicoe Muller*) for their livelihood. These tribes used ecotone and steppe areas of and did not settled in the Andean forests, although there are some examples of communities who lived associated with *Araucaria araucana (Molina) K. Koch* forests in northern Patagonia. Lenga forests, located at higher altitudes, were only occasionally used as firewood in the journeys crossing the Andes (Musters Chaworth, 1871). In Tierra del Fuego, unlike continental Patagonia, guanaco used lenga forests as part of its habitat, perhaps due to the absence of its natural predator, the puma (*Puma concolor*  Linnaeus). Some Indian tribes lived much of the year in these interior forests, while others were established on the shores of the Beagle Channel, all surrounded by lenga forests. In this region, the use of lenga for small constructions and canoes, although in small scale, has been reported (Bridges, 2000). The major effect of indigenous peoples on Patagonian forests has been the recurrent employment of fire, either for hunting purposes or used as a communications signal (Kitzberger & Veblen, 1999).

During white settlement, cracked poles, rustic tables, or shingles, were widely used products from lenga forests, but undoubtedly, fire was the most devastating factor affecting them. In the Argentine sector of Tierra del Fuego, an estimated 20,000 ha were burnt in the early twentieth century. Contemporarily and in an attempt to open land for sheep raising, pioneers in the Chilean Patagonia initiated what could now be called catastrophic fires, burning large portions of lenga woodlands (2.8 million ha, Fajardo & McIntire, 2010), reducing their original area by a half (Otero Durán, 2006). In the rest of its distribution area, thousands of hectares were also burnt, although reliable data are not available (Willis, 1914). The recovering of lenga forests after those fires depended on a multiplicity of factors, among which the availability of safe sites (*sensu* Harper, 1977) for seed germination and seedling establishment, and the grazing pressure exerted on the burned sites played a crucial role. The outcomes in former lenga forests were then open fields to raise sheep or the slow recovery of lenga forests. After that beginning and in the mid 40´s, factors such as the strengthening of national protected areas, the decline of sheep production and the displacement of rural populations modified this process of impoverishment or forest clearance, at least at regional level. Though, the lenga forests that were formerly used as summer ranges for sheep gradually changed to cattle grazing areas. It is interesting to note that the introduction of cattle ranching in the area has a vague origin, as the early explorers (Musters Chaworth, 1871), cite the existence of wild cattle in the forests of the region already in 1870, possibly coming from Valdivia, Chile (settled around 1600), or escaped from the cattle drives that native communities transported from Argentina to Chile.

#### **2.2 The beginnings of industrial use: High grading**

The first forest industries installed in the early twentieth century, either for medium or small sawmills, or for wood veneer production, were characterized by softly logging, cutting only healthy, medium-sized trees. Stem rots, caused mostly by fungi of the genera *Postia* and *Piptoporus*, is a very common phenomenon that affects lenga trees, being very important in old age trees. This determined that in virgin forests, only a small proportion of trees contained good quality timber. For that reason and in general, forest workers used to cut down only trees in good health status, medium-sized (40 - 50 cm DBH), which generally did not exceed 10% of forest trees in a stand. This type of "soft logging" was locally known as "floreo" (high grading).

#### **2.3 Forest management plans**

48 Sustainable Forest Management – Current Research

The objective of this chapter was to analyze the evolution of productive schemes of lenga forests along their history of use, which will help us understand the overlap of strains on this resource, impacts on their conservation status, and the difficulties that currently have the implementation of sustainable management systems. For this purpose, we got information derived from published analyses, statistical records of the Forest Administration, analyses of historical harvesting, and of the impacts of livestock on forest regeneration. This information is presented for two contrasting situations, located one in the northern lenga distribution area in Chubut province and the other in its southern

The original inhabitants of continental Patagonia were mostly nomadic Indian tribes that depended largely on the guanaco (*Lama guanicoe Muller*) for their livelihood. These tribes used ecotone and steppe areas of and did not settled in the Andean forests, although there are some examples of communities who lived associated with *Araucaria araucana (Molina) K. Koch* forests in northern Patagonia. Lenga forests, located at higher altitudes, were only occasionally used as firewood in the journeys crossing the Andes (Musters Chaworth, 1871). In Tierra del Fuego, unlike continental Patagonia, guanaco used lenga forests as part of its habitat, perhaps due to the absence of its natural predator, the puma (*Puma concolor*  Linnaeus). Some Indian tribes lived much of the year in these interior forests, while others were established on the shores of the Beagle Channel, all surrounded by lenga forests. In this region, the use of lenga for small constructions and canoes, although in small scale, has been reported (Bridges, 2000). The major effect of indigenous peoples on Patagonian forests has been the recurrent employment of fire, either for hunting purposes or used as a

During white settlement, cracked poles, rustic tables, or shingles, were widely used products from lenga forests, but undoubtedly, fire was the most devastating factor affecting them. In the Argentine sector of Tierra del Fuego, an estimated 20,000 ha were burnt in the early twentieth century. Contemporarily and in an attempt to open land for sheep raising, pioneers in the Chilean Patagonia initiated what could now be called catastrophic fires, burning large portions of lenga woodlands (2.8 million ha, Fajardo & McIntire, 2010), reducing their original area by a half (Otero Durán, 2006). In the rest of its distribution area, thousands of hectares were also burnt, although reliable data are not available (Willis, 1914). The recovering of lenga forests after those fires depended on a multiplicity of factors, among which the availability of safe sites (*sensu* Harper, 1977) for seed germination and seedling establishment, and the grazing pressure exerted on the burned sites played a crucial role. The outcomes in former lenga forests were then open fields to raise sheep or the slow recovery of lenga forests. After that beginning and in the mid 40´s, factors such as the strengthening of national protected areas, the decline of sheep production and the displacement of rural populations modified this process of impoverishment or forest clearance, at least at regional level. Though, the lenga forests that were formerly used as summer ranges for sheep gradually changed to cattle grazing areas. It is interesting to note that the introduction of cattle ranching in the area has a vague origin, as the early explorers (Musters Chaworth, 1871), cite the existence of wild cattle in the forests of the region already in 1870, possibly coming from Valdivia, Chile (settled around 1600), or escaped from the cattle drives that native communities

distribution area in Tierra del Fuego.

communications signal (Kitzberger & Veblen, 1999).

transported from Argentina to Chile.

**2.1 Pre-industrial**

The first Argentine Forest Law was put in force in 1948. While the concept of forest management, as a synonym of timber production, was prevalent in that law, it included articles about protection of soil, water and biodiversity. Although it mandated for the implementation of Forest management plans, its principles and regulations were applied sparingly. As a result, logging continued in public forests in an unplanned way. In the mid 50´s of the XXth century, the first forest management plans were designed and applied by Croat forest engineers, who arrived to Argentina after the World War II. These plans represented a breakthrough for the understanding of lenga forests, but had little practical effects on forest management due to the weaknesses of the Administrative forestry services of the Patagonian provinces.

By the 80's, the practice of giving access to cut lumber in public or private forests depended on the approval of forest management plans by the provincial forest service, practice that became usual. However, these were just cutting plans, without long term planning horizon and being controlled at different levels of implementation.

Silvicultural aspects were changing over time with the evolution of knowledge about forests dynamics, from the early experiences on shelterwood systems in Chile (Cruz M. & Schmidt, 2007), clear-cut in Argentina (Mutarelli & Orfila, 1971), to the currently used alternatives, ranging from a group selection system (Bava & López Bernal, 2005) up to a variation of shelterwood systems with dispersal and-or aggregate retention (Martínez Pastur et al., 2009).

#### **2.4 Cattle**

As already mentioned, the first activity developed in Patagonian was sheep ranching. Near the Andes, the usual ranching scheme was a system that alternated winter grazing (locally called invernadas) in low areas with summer grazing areas at higher altitudes in the forest (called veranadas). There are plenty of examples of this system in mountain areas around the world. In the mid-twentieth century, with increasing population established in the area, cattle raising was becoming important, with the same production scheme.

In lenga forest ecosystems of Patagonia, herbivory causes severe impacts, because this species is palatable to both wild (camelidae, deer and leporidae), and domestic livestock, and heavy grazing can prevent forest regeneration (Veblen et al., 1996). In Argentina, lenga forests suitable for timber production are mainly concentrated in the provinces of Chubut and Tierra del Fuego. Lenga forests in the province of Chubut are also a very important part of traditional cattle management, which similarly to what formerly occurred with sheep, alternates winter fields in the steppe with summer fields at the mountains (York et al., 2004).

Sustainable Management of Lenga

et al., 2009).

(*Nothofagus pumilio*) Forests Through Group Selection System 51

extraction, by limiting the numbers of individuals or the volume to be harvested (Becking, 1995). However, the real practice was a selective extraction of the best stems (high-grading) without control policies that would ensure the regeneration and future productive potential of the forest, affecting negatively the productive quality of large areas. For this reason, between the fifteenth and eighteenth centuries this type of logging was progressively sidelined (Puettman et al., 2009), and new forest practices, such as clear-cutting, emerged (Becking, 1995). In the early nineteenth century, an alternative selection system was formalized for various regions of Europe, where clear-cuts were banned and where the landowners of small forest stands were especially interested in the high frequency of harvesting (short cutting cycles) thus maintaining a continuous cash flow (Puettman

As mentioned in the previous section, the historical context of lenga forests in Patagonia, and particularly in the north of its distribution, is in some ways comparable to the origins of the implementation of selective cuts. The predominance of small and medium producers, the low productivity of these forests and the low control capacity of state agencies has meant that in most cases the harvest have been a high-grading, often of low intensity. Thus the GSS, where harvesting is simultaneous with other silvicultural tasks (such as thinning or regeneration release) on the one hand represents an economically feasible objective for local

Moreover, the prolonged rotation periods needed for lenga forests and the brief history of the implementation of these schemes in Patagonia prevents direct observation of long-term management examples. Given this situation, models of conservation and sustainable management based on emulation of natural disturbance regimes are very attractive for

From this view, various management systems have been proposed through intense felling as clear-cuts or shelter-wood cuttings (Arce et al., 1998, Martínez Pastur et al., 2009); with the intention of imitating mass disturbances that naturally occur, especially in southern Patagonia. However in Chubut province, the rainfall regime with wet winters and prolonged dry periods in summer, prevents the proper regeneration establishment in large areas subject to direct sunlight (Rusch, 1992). For this reason, an adaptation of Group Selection System (1997) is currently proposed for these sites, imitating the predominant disturbance of gap dynamics (Bava, 1999, Veblen & Donoso, 1987, Veblen et al., 1981, Veblen et al., 1980). This promotes the establishment of regeneration patches formed by felling from

The minimum unit for the application of different treatments in a group selection system is the "forest patch" or "canopy gap". However, the definition of canopy gap or its size is often unclear. On one hand, there are different definitions of the "canopy gap limit" and on the other, there are various ways to simplify its form. Additionally, there are several field methods for gap size measurement. López Bernal et al. (2010) compared different ways of

i. Gap limit definitions: there are two main schools of thought defining this parameter. One is proposed by Brokaw (1982), who defined the gap as a "hole" in the forest that extends across all levels to an average height of two meters above the ground, and

producers, and on the other a simplification of the control tasks posed by the state.

developing sustainable management practices (Perera et al., 2004).

one to six trees (Antequera et al., 1999, López Bernal et al., 2003).

**3.2 Adaptation of GSS to** *N. pumilio* **forests**

**3.2.1 Definition of canopy gap**

this three issues, specifically:

Therefore, 19 % of the forests suitable for timber production are potentially degraded by cattle grazing (Bava et al., 2006). In Tierra del Fuego, by contrast, is the wild guanaco (*L. guanicoe*) which has a negative impact on regeneration. This impact has been reported especially in forests located northwards of Fagnano Lake and in the Chilean side of the Isla Grande de Tierra del Fuego (Cavieres & Fajardo, 2005).

It is possible to distinguish between direct and indirect effects on forest regeneration caused by large herbivores. The direct consumption of seedlings keeps the lenga regeneration stunted (Perera et al., 2004) and multi-stemmed (Bava & Rechene, 2004). The consumption of other species may cause a decrease in the diversity of the understory. The transport of seeds through feces allows the introduction of exotic species (Bava & Puig, 1992). Immersed in lenga forests is frequent to find meadows, locally called "mallines" in the province of Chubut or "vegas" in Tierra del Fuego. These meadows are highly valued by farmers because of their high productivity in forage species. Due to the existence of meadows near the forests, and the little vegetation cover that characterizes the undergrowth of lenga (Lencinas et al., 2008), an intensive use of resources and a great impact on regeneration and understory forest areas close to the meadows has been reported (Quinteros, unpublished data). The changes that livestock generated in the understory, such as increased coverage of grazing tolerant species, mainly exotic, constitutes an indirect effect on the development of lenga regeneration, because the high grass coverage competes for water resources with lenga seedlings, affecting their growth and development (Quinteros, unpublished data).

#### **3. Group selection system in** *N. pumilio* **forests**

#### **3.1 General concepts**

The selective silvicultural systems are characterized by generating uneven-aged stands where regeneration layer strongly interacts with the mature forest, and this interaction could either be favorable or unfavorable for seedlings or saplings of different species (Daniel et al., 1979). With this method, individual trees are removed (or small groups of them), opening small gaps that can be used by tolerant species. Harvesting procedures require frequent partial cuts, where the harvest interval is called "Cutting Cycle" and there is not a rotation age where all production is harvested, as in the even-aged methods (Daniel et al., 1979).

In the Group Selection System (GSS), harvested trees are pooled in small groups (typically up to 10 mature trees), thus creating gaps in the canopy larger than the individual selection cuttings, which are better suited to the requirements of semi-tolerant species, as is the case of lenga (Bava & Rechene, 2004). It also provides some advantages of even-aged stands, as the saplings grow in conditions of intra-cohort competition. This competition favors the production of better shaped stems, while the harvest is partially concentrated, reducing its costs and minimizing the damages from falling trees (Daniel et al., 1979).

Under this scheme, some decisions that have to be taken are (Davis & Johnson, 1987):

The historical origin of this type of management helps gauge its applicability and scope in different productive forest systems. Uneven-aged forest management had its origins in Central Europe, where since the twelfth century exist harvest protocols regulating the forest

Therefore, 19 % of the forests suitable for timber production are potentially degraded by cattle grazing (Bava et al., 2006). In Tierra del Fuego, by contrast, is the wild guanaco (*L. guanicoe*) which has a negative impact on regeneration. This impact has been reported especially in forests located northwards of Fagnano Lake and in the Chilean side of the Isla

It is possible to distinguish between direct and indirect effects on forest regeneration caused by large herbivores. The direct consumption of seedlings keeps the lenga regeneration stunted (Perera et al., 2004) and multi-stemmed (Bava & Rechene, 2004). The consumption of other species may cause a decrease in the diversity of the understory. The transport of seeds through feces allows the introduction of exotic species (Bava & Puig, 1992). Immersed in lenga forests is frequent to find meadows, locally called "mallines" in the province of Chubut or "vegas" in Tierra del Fuego. These meadows are highly valued by farmers because of their high productivity in forage species. Due to the existence of meadows near the forests, and the little vegetation cover that characterizes the undergrowth of lenga (Lencinas et al., 2008), an intensive use of resources and a great impact on regeneration and understory forest areas close to the meadows has been reported (Quinteros, unpublished data). The changes that livestock generated in the understory, such as increased coverage of grazing tolerant species, mainly exotic, constitutes an indirect effect on the development of lenga regeneration, because the high grass coverage competes for water resources with lenga seedlings, affecting their growth and development (Quinteros, unpublished data).

The selective silvicultural systems are characterized by generating uneven-aged stands where regeneration layer strongly interacts with the mature forest, and this interaction could either be favorable or unfavorable for seedlings or saplings of different species (Daniel et al., 1979). With this method, individual trees are removed (or small groups of them), opening small gaps that can be used by tolerant species. Harvesting procedures require frequent partial cuts, where the harvest interval is called "Cutting Cycle" and there is not a rotation age where all production is harvested, as in the even-aged methods (Daniel

In the Group Selection System (GSS), harvested trees are pooled in small groups (typically up to 10 mature trees), thus creating gaps in the canopy larger than the individual selection cuttings, which are better suited to the requirements of semi-tolerant species, as is the case of lenga (Bava & Rechene, 2004). It also provides some advantages of even-aged stands, as the saplings grow in conditions of intra-cohort competition. This competition favors the production of better shaped stems, while the harvest is partially concentrated, reducing its

costs and minimizing the damages from falling trees (Daniel et al., 1979).

Cutting cycle: time between harvest entries on each stand.

Under this scheme, some decisions that have to be taken are (Davis & Johnson, 1987):

Group, patch or gap size: defined in function of objective species requirements.

Reserve growing stock level: residual volume or basal area (BA) immediately after

The historical origin of this type of management helps gauge its applicability and scope in different productive forest systems. Uneven-aged forest management had its origins in Central Europe, where since the twelfth century exist harvest protocols regulating the forest

Grande de Tierra del Fuego (Cavieres & Fajardo, 2005).

**3. Group selection system in** *N. pumilio* **forests**

**3.1 General concepts**

et al., 1979).

harvest.

extraction, by limiting the numbers of individuals or the volume to be harvested (Becking, 1995). However, the real practice was a selective extraction of the best stems (high-grading) without control policies that would ensure the regeneration and future productive potential of the forest, affecting negatively the productive quality of large areas. For this reason, between the fifteenth and eighteenth centuries this type of logging was progressively sidelined (Puettman et al., 2009), and new forest practices, such as clear-cutting, emerged (Becking, 1995). In the early nineteenth century, an alternative selection system was formalized for various regions of Europe, where clear-cuts were banned and where the landowners of small forest stands were especially interested in the high frequency of harvesting (short cutting cycles) thus maintaining a continuous cash flow (Puettman et al., 2009).

As mentioned in the previous section, the historical context of lenga forests in Patagonia, and particularly in the north of its distribution, is in some ways comparable to the origins of the implementation of selective cuts. The predominance of small and medium producers, the low productivity of these forests and the low control capacity of state agencies has meant that in most cases the harvest have been a high-grading, often of low intensity. Thus the GSS, where harvesting is simultaneous with other silvicultural tasks (such as thinning or regeneration release) on the one hand represents an economically feasible objective for local producers, and on the other a simplification of the control tasks posed by the state.

Moreover, the prolonged rotation periods needed for lenga forests and the brief history of the implementation of these schemes in Patagonia prevents direct observation of long-term management examples. Given this situation, models of conservation and sustainable management based on emulation of natural disturbance regimes are very attractive for developing sustainable management practices (Perera et al., 2004).

From this view, various management systems have been proposed through intense felling as clear-cuts or shelter-wood cuttings (Arce et al., 1998, Martínez Pastur et al., 2009); with the intention of imitating mass disturbances that naturally occur, especially in southern Patagonia. However in Chubut province, the rainfall regime with wet winters and prolonged dry periods in summer, prevents the proper regeneration establishment in large areas subject to direct sunlight (Rusch, 1992). For this reason, an adaptation of Group Selection System (1997) is currently proposed for these sites, imitating the predominant disturbance of gap dynamics (Bava, 1999, Veblen & Donoso, 1987, Veblen et al., 1981, Veblen et al., 1980). This promotes the establishment of regeneration patches formed by felling from one to six trees (Antequera et al., 1999, López Bernal et al., 2003).

#### **3.2 Adaptation of GSS to** *N. pumilio* **forests**

#### **3.2.1 Definition of canopy gap**

The minimum unit for the application of different treatments in a group selection system is the "forest patch" or "canopy gap". However, the definition of canopy gap or its size is often unclear. On one hand, there are different definitions of the "canopy gap limit" and on the other, there are various ways to simplify its form. Additionally, there are several field methods for gap size measurement. López Bernal et al. (2010) compared different ways of this three issues, specifically:

i. Gap limit definitions: there are two main schools of thought defining this parameter. One is proposed by Brokaw (1982), who defined the gap as a "hole" in the forest that extends across all levels to an average height of two meters above the ground, and

Sustainable Management of Lenga

**3.2.2 Tree marking guidelines**

matures neighbor trees.

m height.

situation 1.

Stage 3: gap with saplings.

*Xeric sites (Rainfall < 1100 mm/year)*  Stage 0: Patch of mature trees.

trees, mostly from the same cohort.

*Mesic sites (Rainfall > 1100 mm/year)*  Stage 0: Patch of mature trees.

decision between this three alternatives is made:

Stage 1: Gap with seedlings less than 1 m height.

Stage 2: Gap with seedlings higher than 1 m.

(*Nothofagus pumilio*) Forests Through Group Selection System 53

and 30 m, and makes D/H an adaptable parameter. The strong correlation between D/H and incident radiation makes this parameter a good radiation predictor for gaps in a broad range of gap sizes and with canopies of different heights, and represents a useful tool, both

The main strategy proposed by Bava and Lopez Bernal (2005, 2006) for marking in virgin or high graded forests, focuses on trees from which it is currently possible to gain good quality logs, or on young healthy trees showing high timber potential. If these trees exceeded the minimum diameter at the breast height (DBH) of 35 cm (or 40 cm if they had smooth bark), they are felled in order to open or expand the gap, but if they not exceed that diameter, their growth is favored by cutting or girdling competitor trees. Thus, the procedure identifies almost homogeneous small patches within the stand, and depending on their structure, the

*Gap opening:* Operation for the opening of a gap by felling healthy mature trees and girdling

*Gap release:* Operation oriented to release seedlings patches in old gaps by cutting old over-

*Thinning*: Release of young healthy saplings or poles (15-30 cm DBH), by cutting competitors

These general rules can become more specific, taking into account the rainfall level (Figure 3):

i. In a patch composed of mature trees, new gaps with D/H between 1.5 -2 have to be open. We expect that after a rotation of 35 years, the regeneration here will be at least 5

ii. If the available light is not enough for a successful growth, we enlarge the gap up to

iii. In this case, it is possible that the regeneration losses his form and vigor because of inappropriate light conditions, and the opening of a new gap as in situation 0 is needed. In the other case, with the regeneration in good condition, we enlarge the gap up to D/H = 2. In that case we expected height growth rates similar to that mentioned in

iv. If the gap is colonized by seedlings with good growth, there is the possibility that some dominant seedlings with bad form are preventing the proper development of the rest;

v. In this situation the gaps limits are unclear and it is possible to recognize the good quality saplings or poles with the potential to reach commercial sizes (DBH > 40 cm).

vi. In this situation, where individuals from the canopy have reached an age and size that made them suitable for harvesting, new gaps should be open with D / H between 0.8

H/D 2. That allows maximizing the height growth up to 25-30 cm/year.

in this case they should be removed by cutting or girdling.

They have to be released from their main competitors.

to define silvicultural guidelines and to carry out forest ecological studies.

old rotten ones, where a small regeneration patch must grow successfully*.*

whose boundaries are defined as vertical walls. The space calculated by this method is usually called the "canopy gap" (Figure 2). However, this method has been criticized because it underestimates the area affected by the gap (Popma et al., 1988). The other definition was proposed by Runkle (1981), based on the concept of an "expanded gap" whose limits extend to the base of the bordering trees. Runkle argued that this method has the advantage of including the area where light availability is directly and indirectly influenced by the gap.

ii. Calculation methods: regardless of the gap type (i.e. the definition of its limits), there are several methods to calculate or estimate the surface area of a gap. These methods mainly differ in the degree of form simplification, i.e. how well they capture boundary irregularities, moving from ellipses to polygons, octagons or hexadecagons, either with straight sides or with sections of an ellipse (Brokaw, 1982, Green, 1996, Lima, 2005, Runkle, 1981, Zhu et al., 2009).

Fig. 2. Canopy and expanded gap scheme.

iii. Field Methods: Finally, different methods, such as measuring directions and distances from gap center or the triangles method (Lima, 2005), may be applied to measure the variables needed to calculate gap size. These methods may be more or less effective depending on the characteristics (such as understory density and height) of the forest being studied. The optimal field method must also be evaluated in terms of its simplicity of operation, time requirement, necessary tools, etc.

The three issues listed above are all based on the conception of a gap as a surface. The relationship between gap diameter and canopy height has also been used as a reference parameter in some studies (Albanesi et al., 2008, Minckler & Woerheide, 1965, Runkle, 1985), especially where gap creation has been used as a management activity. Canopy height is a parameter with a direct influence on the amount of received radiation. Therefore, the addition of canopy height in any calculation may lead to a significant improvement in the accuracy of gap size estimation.

López Bernal et al. (2010) concluded that the Polygonal Expanded Gap Diameter / dominant canopy Height ratio (from now on D/H) is an expeditious method to characterize gap size. This method not only allows the estimation of the incident radiation, but also the comparison of gaps of different stands and even of different species (Albanesi et al., 2008, OMNR, 2004). The method also incorporates dominant canopy height, which improves gap characterization at different sites. A range for this variable for lenga forests is between 14 and 30 m, and makes D/H an adaptable parameter. The strong correlation between D/H and incident radiation makes this parameter a good radiation predictor for gaps in a broad range of gap sizes and with canopies of different heights, and represents a useful tool, both to define silvicultural guidelines and to carry out forest ecological studies.

#### **3.2.2 Tree marking guidelines**

52 Sustainable Forest Management – Current Research

ii. Calculation methods: regardless of the gap type (i.e. the definition of its limits), there are several methods to calculate or estimate the surface area of a gap. These methods mainly differ in the degree of form simplification, i.e. how well they capture boundary irregularities, moving from ellipses to polygons, octagons or hexadecagons, either with straight sides or with sections of an ellipse (Brokaw, 1982, Green, 1996, Lima, 2005,

Canopy gap

iii. Field Methods: Finally, different methods, such as measuring directions and distances from gap center or the triangles method (Lima, 2005), may be applied to measure the variables needed to calculate gap size. These methods may be more or less effective depending on the characteristics (such as understory density and height) of the forest being studied. The optimal field method must also be evaluated in terms of its

Expanded gap

The three issues listed above are all based on the conception of a gap as a surface. The relationship between gap diameter and canopy height has also been used as a reference parameter in some studies (Albanesi et al., 2008, Minckler & Woerheide, 1965, Runkle, 1985), especially where gap creation has been used as a management activity. Canopy height is a parameter with a direct influence on the amount of received radiation. Therefore, the addition of canopy height in any calculation may lead to a significant improvement in the

López Bernal et al. (2010) concluded that the Polygonal Expanded Gap Diameter / dominant canopy Height ratio (from now on D/H) is an expeditious method to characterize gap size. This method not only allows the estimation of the incident radiation, but also the comparison of gaps of different stands and even of different species (Albanesi et al., 2008, OMNR, 2004). The method also incorporates dominant canopy height, which improves gap characterization at different sites. A range for this variable for lenga forests is between 14

simplicity of operation, time requirement, necessary tools, etc.

indirectly influenced by the gap.

Runkle, 1981, Zhu et al., 2009).

Fig. 2. Canopy and expanded gap scheme.

accuracy of gap size estimation.

whose boundaries are defined as vertical walls. The space calculated by this method is usually called the "canopy gap" (Figure 2). However, this method has been criticized because it underestimates the area affected by the gap (Popma et al., 1988). The other definition was proposed by Runkle (1981), based on the concept of an "expanded gap" whose limits extend to the base of the bordering trees. Runkle argued that this method has the advantage of including the area where light availability is directly and

> The main strategy proposed by Bava and Lopez Bernal (2005, 2006) for marking in virgin or high graded forests, focuses on trees from which it is currently possible to gain good quality logs, or on young healthy trees showing high timber potential. If these trees exceeded the minimum diameter at the breast height (DBH) of 35 cm (or 40 cm if they had smooth bark), they are felled in order to open or expand the gap, but if they not exceed that diameter, their growth is favored by cutting or girdling competitor trees. Thus, the procedure identifies almost homogeneous small patches within the stand, and depending on their structure, the decision between this three alternatives is made:

> *Gap opening:* Operation for the opening of a gap by felling healthy mature trees and girdling old rotten ones, where a small regeneration patch must grow successfully*.*

> *Gap release:* Operation oriented to release seedlings patches in old gaps by cutting old overmatures neighbor trees.

> *Thinning*: Release of young healthy saplings or poles (15-30 cm DBH), by cutting competitors trees, mostly from the same cohort.

These general rules can become more specific, taking into account the rainfall level (Figure 3):

#### *Mesic sites (Rainfall > 1100 mm/year)*

Stage 0: Patch of mature trees.

i. In a patch composed of mature trees, new gaps with D/H between 1.5 -2 have to be open. We expect that after a rotation of 35 years, the regeneration here will be at least 5 m height.

Stage 1: Gap with seedlings less than 1 m height.

Stage 3: gap with saplings.

v. In this situation the gaps limits are unclear and it is possible to recognize the good quality saplings or poles with the potential to reach commercial sizes (DBH > 40 cm). They have to be released from their main competitors.

#### *Xeric sites (Rainfall < 1100 mm/year)*

Stage 0: Patch of mature trees.

vi. In this situation, where individuals from the canopy have reached an age and size that made them suitable for harvesting, new gaps should be open with D / H between 0.8

Sustainable Management of Lenga

maximize their growth.

**3.3 Regeneration requirements 3.3.1 Regeneration establishment**

precipitation, respectively.

**3.3.2 Saplings growth**

Stage 3: gap with saplings.

(*Nothofagus pumilio*) Forests Through Group Selection System 55

x. In these cases the gap limits are unclear and individuals have reached a size that allows us to identify those with potential to reach the appropriate size for harvesting (e.g. DBH greater than or equal to 40 cm). They should be released from its major competitors to

There are three key issues for the success of group selection system in lenga forests. First, regeneration must be installed and growing properly in the gap as to reach their final height with a good stem form. Second, the lateral crown growth of trees bordering the gap must not interfere with the proper development of saplings. Finally, the remaining volume stock after each intervention must maintain its stability until the next harvest. Here we review these three issues, focusing on the aspects that should be taken into account in the definition

Several studies in the northern area of distribution of lenga (xeric sites) have concluded that the establishment of the regeneration of this species is strongly dependent on the availability of water during the growing season. In the drier sites located to the east, regeneration is only installed on microsites that, because of being shadier or because of the protection of course woody debris, remain wetter in summer (Heinemann & Kitzberger, 2006, Heinemann et al., 2000, Rusch, 1992). Thus, the position within the gap is a decisive factor for the recruitment of regeneration in drier sites, whereas in moist sites the position does not influence seedling survival. The same authors found that the initial growth of seedlings in the driest sites was greater in the shady parts of the gap, while in wetter sites the initial growth was higher in the center, concluding that moisture and light availability are the limiting factors for recruitment and early growth for sites with lower and higher levels of

Thus, on the sites without drought stress during the summer, as in the western sector of the distribution of lenga in the province of Chubut, larger gaps will be more adequate, in which the interaction between the canopy and the regeneration is lower. By contrast, in sites with a high hydric deficit during the growing season, located east of the distribution of this species, the facilitating effects in microsites protected from direct sunlight and with lower evapotranspiration by the canopy, outweigh the effect of competition for other resources. As

Having established the regeneration, the requirements for their development change as the seedlings grow in height and their roots explore the soil profile (Callaway & Pugnaire, 2007). Figure 4 shows the values of mean annual increments in height (MAIh) for every level of precipitation and gap size. These values were estimated by a mixed ANCOVA model, in which sapling height was included as a co-variable (López Bernal, unpublished data). During the first 20 years since the gap opening, in the sites with higher levels of precipitation, the dominant seedlings located in the central sector of the gap showed higher growth in larger gaps (p = 0.03 and p = 0.045 for 0-10 and 10-20 years respectively). By contrast, in sites with lower average annual rainfall, there is a tendency for smaller gaps to

of guidelines for forest management of lenga by group selection system.

a result, smaller gaps will present the highest values of recruitment.

show higher height growth, especially during the first 10 years.

Fig. 3. Schematic representation of the marking procedure.

and 1. Situations where seedlings are already present should be preferred. Thus it is expected that after a short cycle of about 35 years regeneration has reached a height of about 3 m.

Stage 1: gap with seedlings less than 1 m height.

vii. Given this situation, it is recommended to take no action unless you notice the presence of an isolated adult tree stocked in the gap (not as border tree), which should be girdled.

Stage 2: gap with seedlings higher than 1 m.

Stage 3: gap with saplings.

54 Sustainable Forest Management – Current Research

Fig. 3. Schematic representation of the marking procedure.

height growth in this condition will reach 15-20 cm/year.

Stage 1: gap with seedlings less than 1 m height.

Stage 2: gap with seedlings higher than 1 m.

they should be girdled.

about 3 m.

girdled.

and 1. Situations where seedlings are already present should be preferred. Thus it is expected that after a short cycle of about 35 years regeneration has reached a height of

vii. Given this situation, it is recommended to take no action unless you notice the presence of an isolated adult tree stocked in the gap (not as border tree), which should be

viii. If the gap has a size from D/H < 1, it should be expanded to reach D/H = 1.5 to 2. The

ix. If the gap is colonized by seedlings with good growth, it is the possible that dominant seedlings with bad form are preventing the proper development of the rest; in this case x. In these cases the gap limits are unclear and individuals have reached a size that allows us to identify those with potential to reach the appropriate size for harvesting (e.g. DBH greater than or equal to 40 cm). They should be released from its major competitors to maximize their growth.

There are three key issues for the success of group selection system in lenga forests. First, regeneration must be installed and growing properly in the gap as to reach their final height with a good stem form. Second, the lateral crown growth of trees bordering the gap must not interfere with the proper development of saplings. Finally, the remaining volume stock after each intervention must maintain its stability until the next harvest. Here we review these three issues, focusing on the aspects that should be taken into account in the definition of guidelines for forest management of lenga by group selection system.

#### **3.3 Regeneration requirements**

#### **3.3.1 Regeneration establishment**

Several studies in the northern area of distribution of lenga (xeric sites) have concluded that the establishment of the regeneration of this species is strongly dependent on the availability of water during the growing season. In the drier sites located to the east, regeneration is only installed on microsites that, because of being shadier or because of the protection of course woody debris, remain wetter in summer (Heinemann & Kitzberger, 2006, Heinemann et al., 2000, Rusch, 1992). Thus, the position within the gap is a decisive factor for the recruitment of regeneration in drier sites, whereas in moist sites the position does not influence seedling survival. The same authors found that the initial growth of seedlings in the driest sites was greater in the shady parts of the gap, while in wetter sites the initial growth was higher in the center, concluding that moisture and light availability are the limiting factors for recruitment and early growth for sites with lower and higher levels of precipitation, respectively.

Thus, on the sites without drought stress during the summer, as in the western sector of the distribution of lenga in the province of Chubut, larger gaps will be more adequate, in which the interaction between the canopy and the regeneration is lower. By contrast, in sites with a high hydric deficit during the growing season, located east of the distribution of this species, the facilitating effects in microsites protected from direct sunlight and with lower evapotranspiration by the canopy, outweigh the effect of competition for other resources. As a result, smaller gaps will present the highest values of recruitment.

#### **3.3.2 Saplings growth**

Having established the regeneration, the requirements for their development change as the seedlings grow in height and their roots explore the soil profile (Callaway & Pugnaire, 2007). Figure 4 shows the values of mean annual increments in height (MAIh) for every level of precipitation and gap size. These values were estimated by a mixed ANCOVA model, in which sapling height was included as a co-variable (López Bernal, unpublished data). During the first 20 years since the gap opening, in the sites with higher levels of precipitation, the dominant seedlings located in the central sector of the gap showed higher growth in larger gaps (p = 0.03 and p = 0.045 for 0-10 and 10-20 years respectively). By contrast, in sites with lower average annual rainfall, there is a tendency for smaller gaps to show higher height growth, especially during the first 10 years.

Sustainable Management of Lenga

saplings density [n/m²]

0

2

4

6

8

(*Nothofagus pumilio*) Forests Through Group Selection System 57

within gap position centre north east south west

Figure 6 represents the two mechanisms of gap healing (i.e. lateral crown growth of bordering trees and regeneration height growth), indicating the time needed for them to close gaps of different sizes (ordinates). In general, larger gaps require more time for healing by crowns growth and less time for healing by regeneration growth. Thus, the curves representing each mechanism are cut at the point corresponding to the gap size that allows the regeneration to reach the canopy just before the crown growth of bordering trees

Thus, the arrow represents the development of a gap in a humid stand, where it is feasible to open a gap with D/H between 1.5 and 2, favoring the seedlings installation and saplings development until its final height. Moreover, the and arrows represent the development of a gap in a xeric stand, where it is necessary to open smaller gaps to ensure seedling establishment, but after a 35 years cutting cycle is necessary to enlarge the gap to

D/H [m/m]

Fig. 6. Necessary time to close gaps of different sizes (D/H) through the height growth of regeneration (solid lines) or the lateral crown growth of the bordering trees (dashed lines) at sites with different dominant height (LCG17, 21 & 25). For references of the arrows , and

0,50 0,75 1,00 1,25 1,50 1,75 2,00

LCG21

saplings growth saplings growth

2

LCG17

3

Fig. 5. Average seedling density at different locations within 20-35 years old gaps.

prevents it. It can also be inferred how long will it take for this to happen (abscissa).

a) high annual average rainfall b) low annual average rainfall

prevent the healing by the lateral crown growth of bordering trees.

LCG21

1

LCG25

0,50 0,75 1,00 1,25 1,50 1,75 2,00

time for gap closure [years]

0

see above.

35

70

105

Summarizing, we can infer that during the first 20 years since the opening of the gaps, the growth of regeneration is determined by light availability in moist sites and water availability in dry sites, with average values of about 22 cm/year and 15 cm/year, respectively, showing a decrease in the differences due to rainfall with the gap age.

Fig. 4. Mean annual increase in height (MAIh) for each precipitation level and gap size class (small gaps = gray bars, large gaps = white bars) along a 35 years cutting cycle. Different symbols indicates significantly different means (Fisher's posthoc test, α = 0.05).

Moreover, the growth data for gaps between 20 and 35 years old shows that at this stage the saplings grew independently of the availability of water, at least enough to keep differences between the sites with higher and lower levels of precipitation. These observations are consistent with several studies which reported that the balance between facilitation and competition interactions usually tends toward negative values when the "facilitated" individual, approaches the age of maturity (for a comprehensive review of this phenomenon see Callaway & Pugnaire, 2007, pp 240).

#### **3.3.3 Saplings density**

Density of seedlings in gaps is often highly variable. During the first years after the creation of gaps, density is strongly determined by the availability of water in the soil, so in places with water deficit during the summer, a greater density is usually observed in the shady gap borders or in microsites caused by the presence of coarse woody debris (Heinemann & Kitzberger, 2006). However, with the subsequent development of the seedlings and the processes of mortality, linked to competence or because of the small disturbances that occur within the gaps (such as total or partial collapse of one of the trees limit), these patterns are lost. For example, it has been observed that in gaps between 20 and 35 years old, significant differences in saplings density between different parts of the gap are not detected (Figure 5, Lopez Bernal et al. Unpublished data). On the other hand, considering only the central part of the gap, there is also great variability, which prevents detect possible influences of gap size or rainfall levels.

#### **3.4 Lateral crown growth of trees bordering the gap**

The average closing rate of gaps due to lateral growth of bordering trees is approx. 19 cm/year. This is high enough so that can occur the gap healing before that regeneration can reach the upper stratum (López Bernal et al. unpublished data).

Summarizing, we can infer that during the first 20 years since the opening of the gaps, the growth of regeneration is determined by light availability in moist sites and water availability in dry sites, with average values of about 22 cm/year and 15 cm/year,

Fig. 4. Mean annual increase in height (MAIh) for each precipitation level and gap size class (small gaps = gray bars, large gaps = white bars) along a 35 years cutting cycle. Different

Moreover, the growth data for gaps between 20 and 35 years old shows that at this stage the saplings grew independently of the availability of water, at least enough to keep differences between the sites with higher and lower levels of precipitation. These observations are consistent with several studies which reported that the balance between facilitation and competition interactions usually tends toward negative values when the "facilitated" individual, approaches the age of maturity (for a comprehensive review of this phenomenon

Density of seedlings in gaps is often highly variable. During the first years after the creation of gaps, density is strongly determined by the availability of water in the soil, so in places with water deficit during the summer, a greater density is usually observed in the shady gap borders or in microsites caused by the presence of coarse woody debris (Heinemann & Kitzberger, 2006). However, with the subsequent development of the seedlings and the processes of mortality, linked to competence or because of the small disturbances that occur within the gaps (such as total or partial collapse of one of the trees limit), these patterns are lost. For example, it has been observed that in gaps between 20 and 35 years old, significant differences in saplings density between different parts of the gap are not detected (Figure 5, Lopez Bernal et al. Unpublished data). On the other hand, considering only the central part of the gap, there is also great variability, which prevents detect possible influences of gap

The average closing rate of gaps due to lateral growth of bordering trees is approx. 19 cm/year. This is high enough so that can occur the gap healing before that regeneration can

symbols indicates significantly different means (Fisher's posthoc test, α = 0.05).

see Callaway & Pugnaire, 2007, pp 240).

**3.4 Lateral crown growth of trees bordering the gap**

reach the upper stratum (López Bernal et al. unpublished data).

**3.3.3 Saplings density**

size or rainfall levels.

respectively, showing a decrease in the differences due to rainfall with the gap age.

Figure 6 represents the two mechanisms of gap healing (i.e. lateral crown growth of bordering trees and regeneration height growth), indicating the time needed for them to close gaps of different sizes (ordinates). In general, larger gaps require more time for healing by crowns growth and less time for healing by regeneration growth. Thus, the curves representing each mechanism are cut at the point corresponding to the gap size that allows the regeneration to reach the canopy just before the crown growth of bordering trees prevents it. It can also be inferred how long will it take for this to happen (abscissa).

Thus, the arrow represents the development of a gap in a humid stand, where it is feasible to open a gap with D/H between 1.5 and 2, favoring the seedlings installation and saplings development until its final height. Moreover, the and arrows represent the development of a gap in a xeric stand, where it is necessary to open smaller gaps to ensure seedling establishment, but after a 35 years cutting cycle is necessary to enlarge the gap to prevent the healing by the lateral crown growth of bordering trees.

Fig. 6. Necessary time to close gaps of different sizes (D/H) through the height growth of regeneration (solid lines) or the lateral crown growth of the bordering trees (dashed lines) at sites with different dominant height (LCG17, 21 & 25). For references of the arrows , and see above.

Sustainable Management of Lenga

a

ab

b

Post-harvest mortality

(% of original Basal Area)

0

**3.6 Case study**

extraction.

or girdling.

10

20

30

40

(*Nothofagus pumilio*) Forests Through Group Selection System 59

50 even-aged

a

ab

b a

bistratified uneven-aged

a

a

Harvest Intensity Low (< 15 %) Intermediate (15-30 %) High (> 30 %)

Fig. 7. Post-harvest mortality by harvest intensity and original stand structure. Different

In this section we present the main results of three trials located in the province of Tierra del Fuego where group selection cut were applied (Bava & López Bernal, 2006). These were implemented in uneven-aged stands with trees from at least three generations and where it

The tree marking was made in November 2003 and the harvest in February 2004, which consisted of felling and bucking of complete stem. During the tree marking, DBH, height and average sawing bole diameter of all marked trees was recorded. At the same time, it was recorded if the tree was felling to open a new gap, to release existing regeneration, or to optimize the growth of young trees. The felling, skid trails opening and bole extraction were carried out in the same campaign. In all three essays harvest tasks were performed by the same team, using directional felling techniques for tree felling and a skidder for bole

After the tree marking, a forest inventory was carried out in each of the three trials. Measurements were performed in 300 m² circular plots spread over a 50 m x 50 m grid, representing a sampling intensity of 1.2 %. In each plot, the DBH of all individuals over 10 cm was measured, recording their sawing potential (indicating the length and medium diameter of the logging portion of the bole), and if it had been marked, whether for felling

All three trials represented intermediate quality sites, located on gentle slopes and possessing uneven-aged structures. The trial 1 had about 360 tree per ha, a BA of 44 m²/ha and a high proportion of overmature trees (DBH over 60 cm) with a low sawing quality. Essay 2 had 430 trees per ha, a BA of 49 m²/ha and presents a high proportion of trees with a DBH between 40 and 60 cm. Essay 3 had 498 trees per ha, a BA of 52 m²/ha with a high

symbols indicate significantly different means (Tuckey's posthoc test, α = 0.05).

was possible to identify the natural process of gap dynamics.

proportion of trees with DBH between 30 and 50 cm (Figure 8).

#### **3.5 Adaptability of GSS to** *N. pumilio* **natural dynamics**

Managing an uneven-aged forest through selection cuts implies a continuous production of wood, so that the remaining stand becomes very important. The regeneration which is established after each harvest and the remaining young trees with timber potential will be the wood source in the coming rotation cycles, so that they constitute the basis for the system´s sustainability (Antequera et al., 1999). That is why post-harvest mortality is a factor of utmost importance.

The harvested stands are affected in their stability, according to the original structure, topography and the type of intervention (Burschel & Huss, 1997, Smith et al., 1997). This weakening effect leads to the fall of trees after the harvest, phenomenon that can seriously affect the quality of the remnant stand. In Tierra del Fuego the windfalls occur even in virgin forests (Rebertus et al., 1997), which poses a logical doubt on the real possibility of implementing this system.

Bava & López Bernal (unpublished data) found that there is no relationship between the manner in which a tree dies (uproot, break or standing death) and the harvest intensity, site quality or stand structure. However, a higher percentage of uprooted trees were observed. The stems that break down correspond to well-anchored individuals, when the wind burden cannot be transmitted by the trunk to the root and soil (Abetz, 1991), or to trees affected by rots, as frequently happens in lenga forests. The uprooting happens when the wind burden is transmitted to the root but cannot be transmitted to the soil (Abetz, 1991). In lenga forests of Tierra del Fuego this can occur in shallow soil stands, when the root system grows superficially (Bava, 1999).

The post-harvest mortality is not significantly related with the percentage of extracted BA. However, when we compare between different stand structures, we note that uneven-aged forests presented minor damage to the even-aged, while the bi-stratified stands presented intermediate damages (Figure 7, ANOVA p = 0.014). These differences may have their origin in phenomena observed at two separate scales: in a stand-scale, uneven-aged forests present a more gradual decline of wind speed from the forest canopy up to the understory, allowing a better adaptation mechanics of trees to wind and giving more stability to the whole (Gardiner, 1995). On the other hand, at the individual-level, Wood (Wood, 1995) observed that the tree develops stems only with the resistance needed to support regular wind intensities, growing adaptively. In this way, the increased heterogeneity of unevenaged stands would provide more opportunities for development of more resistant individuals, which remain after the harvest, and that play a very important role in the stand stability (Burschel & Huss, 1997, Mattheck et al., 1995, Smith et al., 1997). The structural alterations produced by the harvest causes greater exposure of individuals to wind, but in a different way for each one, and would depend on other factors besides the size of the gaps, the h/d value, the felling damages, and homogeneity of the remnant forest.

We have mentioned the importance of the forest stability for sustainability in a selection cuts system, where the productive potential for future interventions is represented by individuals which remain after harvest. In this sense, the results indicate that the postharvest losses are a limiting factor for the implementation of this system, and which would only be advisable by uneven-aged forests. Moreover, the system success also depends on the conscientiously choosing of the trees to cut, and to carry out the harvest operations carefully. If these conditions are present, the group selection system would be a viable alternative, which would maintain the forest cover, with a cutting cycle of approximately 35 years and extracting a timber volume equivalent to the historical average.

Fig. 7. Post-harvest mortality by harvest intensity and original stand structure. Different symbols indicate significantly different means (Tuckey's posthoc test, α = 0.05).

#### **3.6 Case study**

58 Sustainable Forest Management – Current Research

Managing an uneven-aged forest through selection cuts implies a continuous production of wood, so that the remaining stand becomes very important. The regeneration which is established after each harvest and the remaining young trees with timber potential will be the wood source in the coming rotation cycles, so that they constitute the basis for the system´s sustainability (Antequera et al., 1999). That is why post-harvest mortality is a factor

The harvested stands are affected in their stability, according to the original structure, topography and the type of intervention (Burschel & Huss, 1997, Smith et al., 1997). This weakening effect leads to the fall of trees after the harvest, phenomenon that can seriously affect the quality of the remnant stand. In Tierra del Fuego the windfalls occur even in virgin forests (Rebertus et al., 1997), which poses a logical doubt on the real possibility of

Bava & López Bernal (unpublished data) found that there is no relationship between the manner in which a tree dies (uproot, break or standing death) and the harvest intensity, site quality or stand structure. However, a higher percentage of uprooted trees were observed. The stems that break down correspond to well-anchored individuals, when the wind burden cannot be transmitted by the trunk to the root and soil (Abetz, 1991), or to trees affected by rots, as frequently happens in lenga forests. The uprooting happens when the wind burden is transmitted to the root but cannot be transmitted to the soil (Abetz, 1991). In lenga forests of Tierra del Fuego this can occur in shallow soil stands, when the root system

The post-harvest mortality is not significantly related with the percentage of extracted BA. However, when we compare between different stand structures, we note that uneven-aged forests presented minor damage to the even-aged, while the bi-stratified stands presented intermediate damages (Figure 7, ANOVA p = 0.014). These differences may have their origin in phenomena observed at two separate scales: in a stand-scale, uneven-aged forests present a more gradual decline of wind speed from the forest canopy up to the understory, allowing a better adaptation mechanics of trees to wind and giving more stability to the whole (Gardiner, 1995). On the other hand, at the individual-level, Wood (Wood, 1995) observed that the tree develops stems only with the resistance needed to support regular wind intensities, growing adaptively. In this way, the increased heterogeneity of unevenaged stands would provide more opportunities for development of more resistant individuals, which remain after the harvest, and that play a very important role in the stand stability (Burschel & Huss, 1997, Mattheck et al., 1995, Smith et al., 1997). The structural alterations produced by the harvest causes greater exposure of individuals to wind, but in a different way for each one, and would depend on other factors besides the size of the gaps,

We have mentioned the importance of the forest stability for sustainability in a selection cuts system, where the productive potential for future interventions is represented by individuals which remain after harvest. In this sense, the results indicate that the postharvest losses are a limiting factor for the implementation of this system, and which would only be advisable by uneven-aged forests. Moreover, the system success also depends on the conscientiously choosing of the trees to cut, and to carry out the harvest operations carefully. If these conditions are present, the group selection system would be a viable alternative, which would maintain the forest cover, with a cutting cycle of approximately 35

the h/d value, the felling damages, and homogeneity of the remnant forest.

years and extracting a timber volume equivalent to the historical average.

**3.5 Adaptability of GSS to** *N. pumilio* **natural dynamics**

of utmost importance.

implementing this system.

grows superficially (Bava, 1999).

In this section we present the main results of three trials located in the province of Tierra del Fuego where group selection cut were applied (Bava & López Bernal, 2006). These were implemented in uneven-aged stands with trees from at least three generations and where it was possible to identify the natural process of gap dynamics.

The tree marking was made in November 2003 and the harvest in February 2004, which consisted of felling and bucking of complete stem. During the tree marking, DBH, height and average sawing bole diameter of all marked trees was recorded. At the same time, it was recorded if the tree was felling to open a new gap, to release existing regeneration, or to optimize the growth of young trees. The felling, skid trails opening and bole extraction were carried out in the same campaign. In all three essays harvest tasks were performed by the same team, using directional felling techniques for tree felling and a skidder for bole extraction.

After the tree marking, a forest inventory was carried out in each of the three trials. Measurements were performed in 300 m² circular plots spread over a 50 m x 50 m grid, representing a sampling intensity of 1.2 %. In each plot, the DBH of all individuals over 10 cm was measured, recording their sawing potential (indicating the length and medium diameter of the logging portion of the bole), and if it had been marked, whether for felling or girdling.

All three trials represented intermediate quality sites, located on gentle slopes and possessing uneven-aged structures. The trial 1 had about 360 tree per ha, a BA of 44 m²/ha and a high proportion of overmature trees (DBH over 60 cm) with a low sawing quality. Essay 2 had 430 trees per ha, a BA of 49 m²/ha and presents a high proportion of trees with a DBH between 40 and 60 cm. Essay 3 had 498 trees per ha, a BA of 52 m²/ha with a high proportion of trees with DBH between 30 and 50 cm (Figure 8).

Sustainable Management of Lenga

between felling and girdling.

number of marked trees per gap in each essay.

structures.

(*Nothofagus pumilio*) Forests Through Group Selection System 61

young trees (DBH between 20 and 40 cm), while the number of trees per gap increased to 3.4 (Table 2). Moreover, the proportion of gaps or patches with *gap opening*, *gap release* or *patch thinning* interventions differ between essays, pointing out differences in the original stand

Although the three trials were conducted in similar structures, there were significant differences (up to 100%) in the amount of lumber in each. This was reflected in the number of gaps per hectare, but not in their size. The trial with highest harvest intensity (28% of BA) produced twice as sawtimber than the other two, mainly due to felling tending to release young pole trees. This is different from harvests in Chubut province, where the largest

Essay felling girdling Total felling girdling Total 1 28.0 (87%) 4.0 (13%) 32.0 4.8 (96%) 0.2 (4%) 5.0 2 24.4 (86%) 3.8 (14%) 28.2 4.6 (85%) 0.8 (15%) 5.4 3 58.5 (75%) 19.1 (25%) 77.6 11.8 (81%) 2.8 (19%) 14.6 Mean 37.0 (81%) 9.0 (19%) 45.9 7.1 (86%) 1.3 (14%) 8.3

Table 2. Number and proportion of trees and AB marked in each essay, distinguishing

Intervention objective Essay 1 Essay 2 Essay 3 Mean Gap opening (N/ha) 2,0 7,6 7,3 6,7 Gap release (N/ha) 1,3 0,4 5,2 2,7 Patch thinning (N/ha) 7,3 3,2 10,2 6,9 Total gaps / patches per ha 10,7 11,2 22,8 16,4 Felled trees per gap 2,6 2,2 2,6 2,5 Girdled trees per gap 0,4 0,3 0,8 0,7 Total 3,0 2,5 3,4 3,1

Table 3. Number of interventions for gap opening, gap release or patch thinning per ha, and

According to the remnant structures after harvesting, all three trials are able to recover the volume of extracted timber. However, the best choices to implement a group selection system are stands like in trial 3, i.e. a forest with uneven-aged structure and with a high proportion of trees with DBH between 30 and 50 cm. These structures allow a higher proportion of "gap release" and "patch thinning" interventions, which generates a bigger timber harvest in the first cycle, leaving a high number of young trees in optimal growth conditions. The harvest intensity of this trial is very similar to the historical average for Tierra del Fuego province, at about 27% of BA (Bava & López Bernal, 2004), while is

Trees (N/ha) Basal area (m²/ha)

volume portion comes from gap opening cuts (Berón et al., 2003).

Timber stock differences between trials derived in great differences on tree marking. The marking intensity, expressed as a percentage of the original AB, was considerably higher in trial 3 than in trial 1 and 2, proportionally to the differences in timber stock. Moreover, differences in the stand structures generated varying amounts of felled and girdled trees (Table 1).

Fig. 8. Diametric frequency distribution for each trial.

The number and size of gaps or patches that were intervened were also different. In the first two trials, which showed similar productions, about 11 gaps per ha were opened by felling or girdling between 2.5 and 3 trees. In trial 3, with a much higher timber production, the number of opened gaps was also bigger, mainly due to a high proportion of patches with

Timber stock differences between trials derived in great differences on tree marking. The marking intensity, expressed as a percentage of the original AB, was considerably higher in trial 3 than in trial 1 and 2, proportionally to the differences in timber stock. Moreover, differences in the stand structures generated varying amounts of felled and girdled trees

> DBH [cm] 15 25 35 45 55 65 75 85 95 105

The number and size of gaps or patches that were intervened were also different. In the first two trials, which showed similar productions, about 11 gaps per ha were opened by felling or girdling between 2.5 and 3 trees. In trial 3, with a much higher timber production, the number of opened gaps was also bigger, mainly due to a high proportion of patches with

BA [m²/ha]

BA [m²/ha]

BA [m²/ha]

0

3

6

9

12

15

0

3

6

9

12

15

Essay 2

Essay 3

0

3

6

9

12

15 Essay 1

(Table 1).

trees per ha

trees per ha

trees per ha

0

Fig. 8. Diametric frequency distribution for each trial.

50

100

150

0

50

100

150

0

50

100

150

200

young trees (DBH between 20 and 40 cm), while the number of trees per gap increased to 3.4 (Table 2). Moreover, the proportion of gaps or patches with *gap opening*, *gap release* or *patch thinning* interventions differ between essays, pointing out differences in the original stand structures.

Although the three trials were conducted in similar structures, there were significant differences (up to 100%) in the amount of lumber in each. This was reflected in the number of gaps per hectare, but not in their size. The trial with highest harvest intensity (28% of BA) produced twice as sawtimber than the other two, mainly due to felling tending to release young pole trees. This is different from harvests in Chubut province, where the largest volume portion comes from gap opening cuts (Berón et al., 2003).

Table 2. Number and proportion of trees and AB marked in each essay, distinguishing between felling and girdling.

Table 3. Number of interventions for gap opening, gap release or patch thinning per ha, and number of marked trees per gap in each essay.

According to the remnant structures after harvesting, all three trials are able to recover the volume of extracted timber. However, the best choices to implement a group selection system are stands like in trial 3, i.e. a forest with uneven-aged structure and with a high proportion of trees with DBH between 30 and 50 cm. These structures allow a higher proportion of "gap release" and "patch thinning" interventions, which generates a bigger timber harvest in the first cycle, leaving a high number of young trees in optimal growth conditions. The harvest intensity of this trial is very similar to the historical average for Tierra del Fuego province, at about 27% of BA (Bava & López Bernal, 2004), while is

Sustainable Management of Lenga

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much higher than the historical mean for the province of Chubut, of about 15% (Berón, et al., 2003).

#### **4. Conclusion**

The Group Selection System is a valid alternative management system for lenga forests of Argentinean Patagonia. This system emulates one of the most common natural dynamic processes in these forests and provides optimal conditions for regeneration establishment and further development. It is especially recommended for sites with medium to low rainfall levels, where the frequency of large-scale disturbances is low and where the forest presents a natural uneven-aged structure. In Argentina, these situations mainly occur in Chubut province and in the northern part of the lenga distribution in Tierra del Fuego province, where there are already experiences with this type of management.

Moreover, the GSS is compatible with the local production system, dominated by small and medium producers, without financial or technological capacity to afford the costs of intensive harvesting or long-term silvicultural investments. The GSS is adapted to these systems by splitting the turnover age in shorter cutting cycles, giving a more flexible cash flow to these systems, and by allowing that in a single intervention, different silvicultural practices can be carried out. This last point is also an advantage for state control agencies by allowing them to condition the timber extraction to the implementation of other practices that do not generate immediate benefits, such as thinning or regeneration release.

Finally, to ensure the sustainability of forests managed by the GSS, there are at least two aspects that should be especially considered. The first one is that the forester must make his proper interpretation of the natural forest dynamics to decide whether it is feasible or not the implementation this system. The second one implies that to maintain the productive potential for future interventions, logging activities should be conducted with special attention to the remaining forest, using low-impact harvesting technologies.

#### **5. References**

much higher than the historical mean for the province of Chubut, of about 15% (Berón, et

The Group Selection System is a valid alternative management system for lenga forests of Argentinean Patagonia. This system emulates one of the most common natural dynamic processes in these forests and provides optimal conditions for regeneration establishment and further development. It is especially recommended for sites with medium to low rainfall levels, where the frequency of large-scale disturbances is low and where the forest presents a natural uneven-aged structure. In Argentina, these situations mainly occur in Chubut province and in the northern part of the lenga distribution in Tierra del Fuego

Moreover, the GSS is compatible with the local production system, dominated by small and medium producers, without financial or technological capacity to afford the costs of intensive harvesting or long-term silvicultural investments. The GSS is adapted to these systems by splitting the turnover age in shorter cutting cycles, giving a more flexible cash flow to these systems, and by allowing that in a single intervention, different silvicultural practices can be carried out. This last point is also an advantage for state control agencies by allowing them to condition the timber extraction to the implementation of other practices

Finally, to ensure the sustainability of forests managed by the GSS, there are at least two aspects that should be especially considered. The first one is that the forester must make his proper interpretation of the natural forest dynamics to decide whether it is feasible or not the implementation this system. The second one implies that to maintain the productive potential for future interventions, logging activities should be conducted with special

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selección en grupos. *Bosque*, Vol. 24, No. 2, pp. 13-21, ISSN: 0304-8799 Martínez Pastur, G., Lencinas, M. V., Cellini, J. M., Peri, P. L. & Soler Esteban, R. (2009).

*Ecology and Management*, Vol. 201, No. 2-3, pp. 335-347, ISSN: 0378-1127 Green, P. T. (1996). Canopy Gaps in Rain Forest on Christmas Island, Indian Ocean: Size

*of Ecology*, Vol.99, No. 2, pp. 642-650, ISSN: 1365-2745

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compete but help each other to survive: facilitation at the intraspecific level. *Journal*

*Wind and trees*, Coutts, M. P. & Grace, J., pp. 41-59, Cambridge University Press,

silvicultural management in southern *Nothofagus pumilio* primary forests. *Forest*

Distribution and Methods of Measurement. *Journal of Tropical Ecology*, Vol. 12, No.

coarse woody debris on tree regeneration in two environmentally constrasting forests of north-western Patagonia: a manipulative approach. *Journal of*

on the regeneration of Nothofagus pumilio in a xeric old-growth forest of northwestern Patagonia, Argentina. *Canadian Journal of Forest Research*, Vol. 30, No.

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032625-8, New York

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ISBN: 978-0-521-46037-8, Cambridge

3, pp. 427-434, ISSN: 0266-4674

1, pp. 25-31, ISSN: 0045-5067

ISSN: 1572-9710

81, ISSN: 1179-5395

Southern Patagonia. *Forest Ecology and Management*, Vol. 258, No. 4, pp. 436-443, ISSN: 0378-1127

**4**

*Brazil*

**Remote Monitoring for Forest**

*Amazon Institute of People and The Environment-Imazon*

André Monteiro and Carlos Souza Jr.

**Management in the Brazilian Amazon**

Timber harvesting is an important economic activity in the Brazilian Amazon. In 2009, the timber industry produced 5.8 million cubic meters of logwood and generated US\$ 2.5 billion in gross income along with 203,705 direct and indirect jobs (Pereira et al., 2010). Logging in the region is predominantly predatory, and is commonly known as Conventional.  In the conventional method activities are not planned (opening of roads and log decks1, tree felling and log skidding), while with RIL planned management techniques are

The two methods cause impacts ranging from low to severe on the structure and composition of the remaining forest (Gerwing, 2002; John et al., 1996; Pereira Jr. et al., 2002). However, the impacts of predatory logging are two times greater than those of managed logging (John et al., 1996). Among the main impacts are: greater reduction in living aboveground biomass (Gerwing, 2002; Monteiro et al., 2004), risk of extinction for highvalue timber species (Martini et al., 1994), greater susceptibility to forest fires (Holdsworth & Uhl, 1997), increase of vines and pioneer vegetation (Gerwing, 2002; Monteiro et al., 2004)

The impact of timber harvesting can be described by means of forest inventories carried out in the field, with which it is possible to evaluate the structure and composition of the remaining forest (Gerwing, 2002; John et al., 1996; Monteiro et al., 2004). Another method employed is remote sensing, which has advanced over the last decade. In the Amazon, there have been successful tests with satellite images to detect and quantify forest degradation brought about by logging activities in the region (Asner et al., 2005; Matricardi et al., 2007; Souza Jr. et al., 2005). Images with moderate spatial resolution, such as Landsat (30 m) and Spot (20 m), have been used to detect types of logging, damages to the canopy and roads and log decks for harvesting (Asner et al., 2002; Matricardi et al., 2007; Souza Jr. & Roberts, 2005). As for images with high spatial resolution, such as Ikonos (1 to 4 m), they are capable of detecting smaller features of logging, such as small clearings (Read et al., 2003), as well as making it possible to determine the size of log decks and width of roads (Monteiro et al.,

and substantial reduction in carbon stocks (Gerwing, 2002; Putz et al., 2008).

applied at all stages of harvesting (Amaral et al., 1998).

1 Clearings (500 m2) opened in the forest for storing timber.

**1. Introduction**

## **Remote Monitoring for Forest Management in the Brazilian Amazon**

André Monteiro and Carlos Souza Jr. *Amazon Institute of People and The Environment-Imazon Brazil*

#### **1. Introduction**

66 Sustainable Forest Management – Current Research

Smith, D. M., Larson, B. C., Kelty, M. J. & Ashton, P. M. S. (1997). *The practice of silviculture. Applied forest ecology* (9º ed.), John Willey & Sons, ISBN: 0-471-10941-X, New York Tortorelli, L. A. (2009). *Maderas y bosques argentinos* (2° ed), Editorial ACME, ISBN: 978-987-

Veblen, T. T., Ashton, D. H., Schlegel, F. M. & Veblen, A. T. (1977). Plant Succession in a

Veblen, T. T. & Donoso, C. (1987). Alteración natural y dinámica regenerativa de las especies

Veblen, T. T. & Donoso Z., C. (1987). Alteración natural y dinámica regenerativa de las

Veblen, T. T., Donoso Z., C., Kitzberger, T. & Rebertus, A. J. (1996). Ecology of southern

Veblen, T. T., Donoso Z., C., Schlegel, F. M. & Escobar R., B. (1981). Forest dynamics in

Veblen, T. T., Schlegel, F. M. & Escobar R., B. (1980). Structure and dynamics of old-growth

Willis, B. (1914). The Physical Basis of the Argentine Nation. *The Journal of Race Development*,

Wood, C. J. (1995). Understanding wind forces on trees, In: *Wind and trees*, Coutts, M. P. &

York, R. A., Heald, R. C., Battles, J. J. & York, J. D. (2004). Group selection management in

*Journal of Forest Research*, Vol. 34, No. 3, pp. 630-641, ISSN: 0045-5067 Zhu, J., Hu, L., Yan, Q., Sun, Y. & Zhang, J. (2009). A new calculation method to estimate

Timberline Depressed by Vulcanism in South-Central Chile. *Journal of Biogeography*,

chilenas de *Nothofagus* de la región de los lagos. *Bosque*, Vol. 8, No. 2, pp. 133-142,

especies chilenas de *Nothofagus* de la Región de Los Lagos. *Bosque*, Vol. 8, No. 2, pp.

chilean and argentinian *Nothofagus* forests, In: *The ecology and biogeography of Nothofagus forests*, Veblen, T. T., Hill, R. S. & Read, J., pp. 293-353, Yale University

South-central Chile. *Journal of Biogeography*, Vol. 8, No. 3, pp. 211-247, ISSN:

*Nothofagus* forests in the Valdivian Andes, Chile. *Journal of Ecology*, Vol. 68, No. 1,

Grace, J., pp. 133-164, Cambridge University Press, ISBN: 978-0-521-46037-8,

conifer forests: relationships between opening size and tree growth. *Canadian*

forest gap size. *Frontiers of Forestry in China*, Vol. 4, No. 3, pp. 276-282, ISSN: 1673-

9260-69-2, Buenos Aires, Argentina

Press, ISBN: 0-300-06423-3, London

Vol. 4, No. 4, pp. 443-460, ISSN: 10683380

ISSN: 0304-8799

03050270

Cambridge

3630

133-142, ISSN: 0304-8799

pp. 1-31, ISSN: 1365-2745

Vol. 4, No. 3, pp. 275-294, ISSN: 03050270

Timber harvesting is an important economic activity in the Brazilian Amazon. In 2009, the timber industry produced 5.8 million cubic meters of logwood and generated US\$ 2.5 billion in gross income along with 203,705 direct and indirect jobs (Pereira et al., 2010). Logging in the region is predominantly predatory, and is commonly known as Conventional.  In the conventional method activities are not planned (opening of roads and log decks1, tree felling and log skidding), while with RIL planned management techniques are applied at all stages of harvesting (Amaral et al., 1998).

The two methods cause impacts ranging from low to severe on the structure and composition of the remaining forest (Gerwing, 2002; John et al., 1996; Pereira Jr. et al., 2002). However, the impacts of predatory logging are two times greater than those of managed logging (John et al., 1996). Among the main impacts are: greater reduction in living aboveground biomass (Gerwing, 2002; Monteiro et al., 2004), risk of extinction for highvalue timber species (Martini et al., 1994), greater susceptibility to forest fires (Holdsworth & Uhl, 1997), increase of vines and pioneer vegetation (Gerwing, 2002; Monteiro et al., 2004) and substantial reduction in carbon stocks (Gerwing, 2002; Putz et al., 2008).

The impact of timber harvesting can be described by means of forest inventories carried out in the field, with which it is possible to evaluate the structure and composition of the remaining forest (Gerwing, 2002; John et al., 1996; Monteiro et al., 2004). Another method employed is remote sensing, which has advanced over the last decade. In the Amazon, there have been successful tests with satellite images to detect and quantify forest degradation brought about by logging activities in the region (Asner et al., 2005; Matricardi et al., 2007; Souza Jr. et al., 2005). Images with moderate spatial resolution, such as Landsat (30 m) and Spot (20 m), have been used to detect types of logging, damages to the canopy and roads and log decks for harvesting (Asner et al., 2002; Matricardi et al., 2007; Souza Jr. & Roberts, 2005). As for images with high spatial resolution, such as Ikonos (1 to 4 m), they are capable of detecting smaller features of logging, such as small clearings (Read et al., 2003), as well as making it possible to determine the size of log decks and width of roads (Monteiro et al.,

<sup>1</sup> Clearings (500 m2) opened in the forest for storing timber.

Remote Monitoring for Forest Management in the Brazilian Amazon 69

iv. Conventional logging: forest logged selectively and not following planning of the activities mentioned above. Log decks, roads and skidder trails are opened causing

v. Logged and burned: forest logged selectively, without planning, followed by burning. vi. Logged intensely and burned: forest logged selectively in a conventional manner more

To evaluate differences between the variables in the degradation classes we employed the analysis of variance (ANOVA with Type III Sum of Squares) followed by the Tukey's HSD post-hoc test with an individual error rate of 0.05% and with an overall significance of 0.08%

severe damage to the forest.

than once, and later burned.

vii. Burned: forest burned without having been logged.

using the R program (R *Development Core Team*, 2010).

Fig. 1. Transect layout of the forest inventories.

components based on their diameters (cm).

Forest tree species ≥ 10 cm DBH

Pioneer tree species Cecropia sp. Other sp.

< 10 cm DBH

Species group Regression equation Source

Overman et al. (1994) Higuchi & Carvalho (1994)

Nelson et al. (1999) Nelson et al. (1999)

J. Gerwing (data not published)

log(DW)= 0.85+2.57 log(DBH)

ln(DW)= -2.512+2.426 ln(DBH) ln(DW)= -1.997+2.413 ln(DBH)

Table 1. Regression equations used to determine the dry weights (kg) of various forest

In the subsections below, we present the results of characterizing forest degradation for the classes described above. That information is later combined with remote sensing data to evaluate the intensity and quality of logging. In the field we quantified forest degradation

DW= 0.465(DBH)2.202 DW= 0.6\*4.06(DBH)1.76

2007). The use of remote sensing for monitoring forest management plans is of great importance for the Brazilian Amazon, given that logging activities are predominantly predatory and occur in extensive areas that are difficult to access.

Recent studies have shown how to integrate data extracted from satellite images with biomass data collected in the field, which makes it possible to estimate the loss of biomass in the forest submitted to different levels of forest degradation (Asner et al., 2002; Pereira Jr. et al., 2002; Souza Jr. et al., 2009). Our research has made advances in applying those techniques to assess the intensity and quality of logging (Monteiro et al., 2009).

In this chapter, we demonstrate how the impacts of timber harvesting can be characterized by means of forest inventories and combined with satellite images to monitor extensive areas. We also present the remote sensing techniques utilized for detecting, mapping and monitoring logging activities. Finally, we present the results of our system for monitoring forest management plans, applied in Pará and Mato Grosso, the two largest timberproducing States in the Amazon, which respectively account for 44% and 34% of the total produced in 2009 (Pereira et al., 2010).

#### **2. Logging impact characterization based on field surveys**

#### **2.1 Change in structure and composition as a result of forest degradation**

Characterization of the impacts of logging in the field is done by means of forest inventories. To do this, transects or plots are established in the forest to quantify the damages to its structure and composition in terms of soil cover, canopy cover and aboveground live biomass (Gerwing, 2002; John et al., 1996; Monteiro et al., 2004).

In the method developed by Gerwing (2002) 10 m x 500 m transects are opened, in which all individual trees with DBH (Diameter at Breast Height) ≥ 10 cm are sampled. In 10 m x 10 m sub-parcels, located at 50 m intervals along the central line of the transect, all individuals with DBH ≤ 10 cm are sampled. In those sub-parcels the soil cover is assessed, with the percentages of intact soil, soil with residues and disturbed soils being recorded; as well as the canopy cover, with four readings in a spherical densiometer, at 90° intervals, every 50 m along the central axis of the transect (Figure 1).

Additionally, the live biomass above the ground in each transect is estimated, adding together the weight of dry matter from different forest components using alometric equations available in the literature (Table 1). The estimate of biomass for trees < 10 cm is done by multiplying the number of stems in each diameter class by the biomass corresponding to the arithmetic average of the diameter for each class.

The forest inventory was carried out in 55 transects, including 11 in intact forest (reference) and 44 in forests in different classes of degradation due to different log harvesting methods. It was done in the Paragominas and Santarém regions, in the State of Pará, in Sinop, in Mato Grosso, and in Itacoatiara, in Amazonas (Figure 2). Below is a description of intact forest and forests in different classes of degradation according to Gerwing (2002):

2007). The use of remote sensing for monitoring forest management plans is of great importance for the Brazilian Amazon, given that logging activities are predominantly

Recent studies have shown how to integrate data extracted from satellite images with biomass data collected in the field, which makes it possible to estimate the loss of biomass in the forest submitted to different levels of forest degradation (Asner et al., 2002; Pereira Jr. et al., 2002; Souza Jr. et al., 2009). Our research has made advances in applying those

In this chapter, we demonstrate how the impacts of timber harvesting can be characterized by means of forest inventories and combined with satellite images to monitor extensive areas. We also present the remote sensing techniques utilized for detecting, mapping and monitoring logging activities. Finally, we present the results of our system for monitoring forest management plans, applied in Pará and Mato Grosso, the two largest timberproducing States in the Amazon, which respectively account for 44% and 34% of the total

Characterization of the impacts of logging in the field is done by means of forest inventories. To do this, transects or plots are established in the forest to quantify the damages to its structure and composition in terms of soil cover, canopy cover and aboveground live

In the method developed by Gerwing (2002) 10 m x 500 m transects are opened, in which all individual trees with DBH (Diameter at Breast Height) ≥ 10 cm are sampled. In 10 m x 10 m sub-parcels, located at 50 m intervals along the central line of the transect, all individuals with DBH ≤ 10 cm are sampled. In those sub-parcels the soil cover is assessed, with the percentages of intact soil, soil with residues and disturbed soils being recorded; as well as the canopy cover, with four readings in a spherical densiometer, at 90° intervals, every 50 m

Additionally, the live biomass above the ground in each transect is estimated, adding together the weight of dry matter from different forest components using alometric equations available in the literature (Table 1). The estimate of biomass for trees < 10 cm is done by multiplying the number of stems in each diameter class by the biomass

The forest inventory was carried out in 55 transects, including 11 in intact forest (reference) and 44 in forests in different classes of degradation due to different log harvesting methods. It was done in the Paragominas and Santarém regions, in the State of Pará, in Sinop, in Mato Grosso, and in Itacoatiara, in Amazonas (Figure 2). Below is a description of intact forest

i. Intact forest: mature forest (> 40 years) without disturbance, dominated by shade-

ii. Logged without mechanization (Traditional logging): forest logged without the use of skidder tractors, that is, without impact from construction of logging infrastructure: log

iii. Managed logging (Reduced Impact Logging-RIL): forest logged selectively following planning of harvesting activities: forest inventory, opening of decks and roads, felling

techniques to assess the intensity and quality of logging (Monteiro et al., 2009).

**2. Logging impact characterization based on field surveys**

biomass (Gerwing, 2002; John et al., 1996; Monteiro et al., 2004).

corresponding to the arithmetic average of the diameter for each class.

and forests in different classes of degradation according to Gerwing (2002):

along the central axis of the transect (Figure 1).

tolerant species.

decks, roads and skidder trails.

and skidding of trees and transport of logs.

**2.1 Change in structure and composition as a result of forest degradation**

predatory and occur in extensive areas that are difficult to access.

produced in 2009 (Pereira et al., 2010).

To evaluate differences between the variables in the degradation classes we employed the analysis of variance (ANOVA with Type III Sum of Squares) followed by the Tukey's HSD post-hoc test with an individual error rate of 0.05% and with an overall significance of 0.08% using the R program (R *Development Core Team*, 2010).

Fig. 1. Transect layout of the forest inventories.

Table 1. Regression equations used to determine the dry weights (kg) of various forest components based on their diameters (cm).

In the subsections below, we present the results of characterizing forest degradation for the classes described above. That information is later combined with remote sensing data to evaluate the intensity and quality of logging. In the field we quantified forest degradation

Remote Monitoring for Forest Management in the Brazilian Amazon 71

The live biomass aboveground was less in the forest degradation classes compared to the biomass in intact forest; however, no significant differences were found between them. Among individuals with DBH ≥ 10 cm, the logged and burned and intensely logged classes presented 36% lower biomass than the intact forest, followed by the burned class (18%) (Table 2). The lowest biomass for individuals with DBH < 10 cm was also observed in the logged and burned (44%) and intensely logged and burned (11%) classes (Table 2). The biomass in individuals with DBH ≥ 10 cm decreased with increasing degradation. The variation in biomass for individuals with DBH < 10 cm seems to be related to the incidence of pioneer species that tolerate moderate levels of degradation (Gerwing, 2002; Monteiro et al., 2004). The greatest loss of biomass is not related only to the greatest forest degradation. The distance from the first degradation may also influence a greater reduction in biomass (Gerwing, 2002; Monteiro et al., 2004). For example, data collection in the logged and burned forest (biomass for individuals ≥ 10 cm and < 10 cm = 232 t ha-1 and 5 t ha-1, respectively) occurred approximately 2.5 years after the first degradation event, while in the intensely logged and burned forest (biomass for individuals ≥ 10 cm and < 10 cm = 234 t ha-1 and 8 t

ha-1, respectively), it occurred 16 years after the first degradation event.

**(c) Managed logging (n=14)**

96 (20) c

23 (12) a

10 (9) a

**cover (%)** 95 (3) a 87 (9) b 96 (2) a 92 (6) a 75 (8) c 86 (2) a 88 (1) d

342 (52) a

9 (1) a

 Means presented with standard deviation noted parenthetically. In the ground cover, canopy cover and biomass values, different forest class letters denote significant differences among stand classes at

Table 2. Comparison of ground cover, canopy cover and biomass among intact forest and

Moderate satellite imagery such as Landsat Thematic Mapper (30-meters pixel size) and Spot Multispectral (20 meters) has been used to detect and map the impacts of selective

**3. Remote sensing techniques to enhance and detect timber harvesting**

**(d) Conventional logging (n=8)**

92 (15) ac

13 (11) a

13 (11) a

321 (12) a

11 (1) a

**(e) Logged and burned (n=4)**

75 (7) d

26 (10) a

7 (6) a

232 (11) a

5 a

**(f) Heavily logged e burned (n=5)**

4 (5) ef

0 a

96 (5) b

234 (23) a

8 a

**(g) Burned (n=4)**

22 (19) f

25 (44) a

53 (49) c

299 (14) a

9 a

**(b) Nonmechanized logging (n=9)**

87 (22) b

23 (23) a

3 (4) a

347 (33) a

10 (2) a

P<0.05 utilizing Tukey's HSD post-hoc test, with a global significance level of 0.8

degraded forest in the States of Pará, Mato Grosso and Amazonas in Brazil\*

**2.1.2 Change in the live aboveground biomass**

**(a) Intact (n=11)**

95 (6) a

5 (6) a

0 a

365 (50) a

9 (2) a

**Ground cover (total area (%))**  Intact vegetation

Woody debris

Disturbed soil

**Aboveground live biomass (t ha-1)**

Live trees ≥ 10 cm

Live trees < 10 cm

**Canopy**

DBH

DBH

\*

related to soil disturbance (intact vegetation, residues and disturbed soil), canopy cover and aboveground biomass because those indicators present a direct relation with remote sensing data (Souza Jr. et al., 2009).

Fig. 2. Location of the forest transects sites.

#### **2.1.1 Soil disturbance and canopy cover**

The evaluation of soil disturbance (intact vegetation, residues and disturbed soil) and canopy cover in the field is crucially important, since those results directly influence the results of the satellite images. The greater the soil disturbance and the smaller the canopy cover of the degraded forest, the greater will be the signal for this damage in the image. Our results show that the area of intact vegetation was smaller in the classes with greater degradation. The smallest percentage of intact vegetation was observed in the intensely logged and burned class (4%), followed by burned forest (22%), with these presenting a significant difference in relation the intact forest and to the classes with less degradation. The quantity of residues in the soil was greater in the logged and burned forest (26%), followed by the burned forest (25%), however no significant differences were found between these classes and intact forest. The area of disturbed forest was greater in the intensely logged and burned forest (96%) and the burned forest (53%), presenting a significant difference in relation to the intact forest and the other degradation classes. The logged and burned class presented the lowest canopy cover (75%), with a significant difference in relation to the intact forest and to the classes with less degradation (Table 2).

#### **2.1.2 Change in the live aboveground biomass**

70 Sustainable Forest Management – Current Research

related to soil disturbance (intact vegetation, residues and disturbed soil), canopy cover and aboveground biomass because those indicators present a direct relation with remote sensing

The evaluation of soil disturbance (intact vegetation, residues and disturbed soil) and canopy cover in the field is crucially important, since those results directly influence the results of the satellite images. The greater the soil disturbance and the smaller the canopy cover of the degraded forest, the greater will be the signal for this damage in the image. Our results show that the area of intact vegetation was smaller in the classes with greater degradation. The smallest percentage of intact vegetation was observed in the intensely logged and burned class (4%), followed by burned forest (22%), with these presenting a significant difference in relation the intact forest and to the classes with less degradation. The quantity of residues in the soil was greater in the logged and burned forest (26%), followed by the burned forest (25%), however no significant differences were found between these classes and intact forest. The area of disturbed forest was greater in the intensely logged and burned forest (96%) and the burned forest (53%), presenting a significant difference in relation to the intact forest and the other degradation classes. The logged and burned class presented the lowest canopy cover (75%), with a significant difference in relation to the intact forest and to the classes with less degradation (Table 2).

data (Souza Jr. et al., 2009).

Fig. 2. Location of the forest transects sites.

**2.1.1 Soil disturbance and canopy cover**