%0 Journal Article %J Journal of Arid Environments %D 2002 %T Hydrology-vegetation interactions in areas of discontinuous flow on a semi-arid bajada, Southern New Mexico %A Wainwright, John %A Parsons, Anthony J. %A Schlesinger, William H. %A Athol D. Abrahams %K article %K articles %K carbon, Larrea %K hydrology, deposition %K hydrology, erosion %K hydrology, Larrea %K hydrology, processes %K hydrology, shrubs %K hydrology, xylem-pressure potential %K hydrology,infiltration %K hydrology,runoff %K journal %K journals %K Larrea, xylem-pressure potential %K nitrogen, Larrea %K plant, 13C %K plant, 15N %K xylem-pressure potential, hydrology %X

Flows on a bajada surface in the Chihuahuan Desert of New Mexico show a discontinuous pattern, with alternating areas of channelization and deposition. Based on their planform appearance, we have termed the depositional areas 'beads'. Instrumented catchments demonstrated that in comparison to 'normal' dendritic catchments, the beads show net infiltration in all but the largest flow events. Net accumulation of the bead surface appears to occur in years of lower than average rainfall, but the surface is dynamic and suffers net erosion in wetter years. The beads have significantly higher total vegetation covers, and contain higher proportions of grass species (Muhlenbergia porteri) as well as the creosotebush that characterizes the bajada surface in general. Creosotebush in the beads show consistently lower values of ä13C, suggesting that they are less moisture stressed than creosotebush elsewhere on the bajada. Values of ä15N are higher in the bead creosotebush, suggesting higher rates of soil-nitrogen transformations and greater loss of nitrogen to the atmosphere by denitrification. Both of these factors are again consistent with higher infiltration and thus moisture contents in the beads. In contrast, xylem-pressure potentials in creosotebush in the bead taken before the summer monsoonal season suggest that plants within the bead are more moisture stressed than those outwith the bead. Four possible explanations are offered for this apparent discrepancy: the greater cover and biomass of plants in the bead leads to higher stresses at the end of the drought period; spatial variability in soil texture means that some areas of the bead retain less moisture; more available water in the bead goes to the grass plants that concentrate their roots near the surface; and there is greater competition in the bead during times of drought stress. Overall, these results are compatible with an 'islands of fertility' interpretation of desertification operating in the American Southwest, albeit on a larger spatial scale than usually attributed. The concentrations of nutrient, water and seed resources may mean that these sites are favourable for attempts to reverse the desertification process. However, they appear dynamic with life cycle of about 30 years. ©2002 Elsevier Science Ltd.

%B Journal of Arid Environments %V 51 %P 319-338 %8 2002 %G eng %U files/bibliography/JRN00357.pdf %M JRN00357 %L 00802 %) In File (03/25/03) %R 10.1006/jare.2002.0970 %F 1175 %0 Journal Article %J Oecologia %D 1989 %T Interplant variation in creosotebush foliage characteristics and canopy arthropods %A David C. Lightfoot %A Walter G. Whitford %K arthropod, Larrea %K article %K articles %K journal %K journals %K Larrea, arthropods %K Larrea, nitrogen %K nitrogen, Larrea %K phytophagous insect %K plant-insect interactions %X

We conducted a field study to test the hypothesis that creosotebush (Larrea tridentata) shrubs growing in naturally nutrient-rich sites had better quality foliage and supported greater populations of foliage arthropods than shrubs growing in nutrient-poor sites. Nutrient-rich sites had significantly higher concentrations of soil nitrogen than nutrient-poor sites. Multivariate analysis of variance revealed significant differences between high nutrient and low nutrient shrubs based on a number of structural and chemical characteristics measured. High nutrient shrubs were larger, had denser foliage, greater foliage production, higher concentrations of foliar nitrogen and water, and lower concentrations of foliar resin than low nutrient shrubs. Numbers of foliage arthropods, particularly herbivores and predators, were significantly higher on high nutrient shrubs. Shrub characteristics and foliage arthropod abundances varied considerably from shrub to shrub. Shrub characteristics representing shrub size, foliage density, foliage growth, and foliar nitrogen and water concentrations were positively correlated with arthropod abundances. Foliar resin concentrations were negatively correlated with foliage arthropod abundances. The positive relationship between creosotebush productivity and foliage arthropods is contradictory to the tenet that physiologically stressed plants provide better quality foliage to insect herbivores.

%B Oecologia %V 81 %P 166-175 %8 1989 %G eng %U files/bibliography/JRN00099.pdf %M JRN00099 %L 00178 %R 10.1007/BF00379801 %F 517 %0 Journal Article %J Oecologia %D 1988 %T The effect of varying nitrogen and phosphorus availability on nutrient use by Larrea tridentata, a desert evergreen shrub %A Lajtha, Kate %A Klein, Melanie %K article %K articles %K journal %K journals %K Larrea, germination, nitrogen %K Larrea, germination, phosphorus %K Larrea, nutrients %K nitrogen, Larrea %K nutrient resorption efficiency %K nutrient use efficiency %K phosphorus, Larrea %K seed, germination %X In a phytotron study of the effects of nitrogen and phosphorus supply ration on nutrient uptake and use by Larrea tridentata, seedlings responded to increases in N and P availability with increases in leaf size, total biomass, and leaf nutrient concentration, and with decreases in root:shoot ratio. N and P use efficiency decreased with increasing N and P availability, respectively, but increased with increasing availability of the other nutrient, suggesting that Larrea responds both to the absolute and to the relative availability of limiting nutrients. Absolute amounts of N and P resorption, as well as N and P resorption efficiencies did not demonstrate a significant trend with nutrient availability, and there was no evidence of significant interactions between the two nutrients. More studies of the effects of nutrient interactions in the cycling and use of nutrients by different plant species are needed before more general conclusions can be drawn. %B Oecologia %V 75 %P 348-353 %8 1988 %G eng %L 00166 %F 497 %0 Journal Article %J Ecology %D 1987 %T Variation in insect densities on desert creosotebush: is nitrogen a factor? %A David C. Lightfoot %A Walter G. Whitford %K arthropod, Larrea %K arthropod, list %K article %K articles %K insect, phytophagous %K journal %K journals %K Larrea, arthropods %K list, arthropod %K nitrogen amendment %K nitrogen, Larrea %K phytophagous insect %K rainfall simulation %K water amendment %X

A field experiment was conducted to assess the effects of nitrogen and water on the densities and taxonomic and trophic compositions of arthropods on the foliage of desert creosotebush (Larrea tridentata). Nitrogen and water were manipulated through a series of fertilizer and irrigation treatments applied to naturally growing creosotebush shrubs at a site in the northern Chihuahuan Desert. Water with nitrogen, and nitrogen fertilization alone, significantly increased creosotebush foliage production and foliar nitrogen contents. Foliage production, foliar nitrogen contents, and numbers of foliage arthropods were all higher in the late spring than in the mid or late summer. Numbers of foliage arthropods increased significantly on fertilized plants in the late spring. Water treatments alone had no effect on numbers of foliage arthropods, but a positive water-fertilizer interaction effect on numbers of foliage arthropods was evident in the late spring. Overall, there were significant positive correlations between foliage production, foliar nitrogen contents, and foliage arthropod densities. Photophagous sap-sucking insects accounted for the majority of arthropods on creosotebush, and their densities varied most in relation to foliage production and foliar nitrogen contents. Results of our study demonstrated that sap-sucking phytophagous insects are more responsive than leaf-chewing insects to increased nitrogen content of creosotebush foliage, and that much of the between-plant variation in densities of phytophagous insects within a stand of creosotebush may be due to sap-sucking insects tracking variable foliar nitrogen.

%B Ecology %V 68 %P 547-557 %8 1987 %G eng %U files/bibliography/JRN00064.pdf %M JRN00064 %L 00181 %R 10.2307/1938460 %F 520