Energy Considerations: The Flow Of Life Through
Stream-side Foliage And Its Role In Stream Ecology
along the river in the fall
Tree-lined stream banks are essential for the
life of the freestone river. The trees, bushes and shrubs that
grow there and the many roles they play in helping to maintain
the integrity of those banks cannot be emphasized often enough.
Tree’s root systems act like anchors for the soil and rock,
two essential ingredients needed for maintaining the physical
course of the river. Siltation
is an unusual event for rivers that run through intact hardwood
or boreal forests, even after heavy rains. In contrast, it is
commonplace for rivers that have had their stream-side plants
removed, or greatly reduced. The consequences of soil from the
bank repeatedly washing into the river are devastating for the
macro invertebrates. Silt gathers around in-stream rocks and other
bottom structure, and limits the amount of space that is available
for clinging larval forms of macro invertebrates. Oxygen levels
are depleted whenever soil washes into the water. It is hard to
sit on the bank and watch as a river with extensively defoliated
banks changes color to that of a good cup of strong coffee with
cream during a summer thunder storm, as rivulets of soil-laden
water rush out of the surrounding hillsides into the main stem.
Such is the case for many northeastern American rivers, particularly
so now that the floods of 1994 and 1996 have removed so many trees
from their watersheds.
Trees shade the river in summer months and function
as nature’s air conditioners. Why this ecosystem function
for the river is routinely ignored by those living near rivers
is a mystery, since we never fail to replace a faulty air conditioner
in our own homes, and we always seek the cool refuge of shade
when we go on a picnic or park our cars.
Thermal pollution events are common among rivers that are
missing significant numbers of trees along their banks.
The leaves of trees harbor an astonishing variety
of insects and arachnids (spiders, and their kin) that are constantly
falling into the water, providing a much needed supplemental protein
source for fish at times when aquatic insect hatches are reduced.
This is particularly so in the height of summer during daylight
When a tree dies of old age and falls into the river, or an unusual
storm rips them from the bank, the amount of in-stream organic
material they supply for the larvae and nymphs of aquatic insects
can be significant. Trees begin to decay the moment they enter
the water, and nutrients are mobilized by leaching which directly
aid in the growth of essential microbial and macro invertebrate
communities. Dead trees and branches act like a slow time-release
capsule of energy that may take ten or twenty years to be fully
utilized. Dead trees also provide protective cover for trout,
helping them to avoid predators.
Matte of rotting leaves
in an eddy
Dead trees create openings in the forest canopy.
Then pioneer plant species that are shade
intolerant germinate and grow, filling up the gaps (succession).
When they grow to a certain height, they cast enough shade to
stimulate the growth of shade
tolerant plants (trees).
tree species. Eventually, the tree grows to a
height above the shade intolerant shrubs and bushes, causing these
species to die, creating a bare forest floor for other plants
(ferns, wild flowers, etc.) to colonize. If for some reason, pioneer
plant species fail to fill in the missing space along the bank,
(unusual flooding, killing frosts, over-browsing, etc.), then
within the first several seasons after the death of the tree,
the river re-shapes that part of itself by erosion. But a barren
stretch of riverbank is susceptible to damage. Each rain removes
(e.g., calcium, potassium, nitrates and other organic compounds),
and siltation increases until plants can stabilize it.
Lastly, and most critical to the productivity
of the river, the leaves that fall into the water of most freestone
rivers provide up to 60% of the annual required energy in-put
for macro invertebrates.Reduced in-put of leaves results in very
few insects. Low numbers of insects cannot support healthy populations
of trout. So a good saying for remediation
where trees are needed is:
“Plant a tree and save a trout”
This is one long-term project in which we can all participate,
just in case we’re looking for something to do on Arbor
Day each Spring.
What good is a tree? They are so good that we cannot afford to
under-value them as the keepers of the riverbank and the river,
itself. Without streamside trees lining the entire bank on both
sides, a river cannot operate at maximum efficiency. To insure
that each and every river bank is maintained as intact as is humanly
possible is good stewardship, and at the same time, increases
our chances of living out our lives in greater harmony with the
processes of nature that got us here to begin with.
Arbor Day is celebrated across the United States each spring
and results in thousands of new trees being planted. The Roscoe
Central School has been involved with tree planting since 1995
(see: Arbor Day and Trout In The Class Room on this site). The
children are always asked: “What good is a tree”?
Eventually, they all come to realize that a tree along the Beaver
Kill is essential for good trout fishing. Others have thought
about this question, as well. An artist who participated in the
Arbor Day celebration at the National Arts Club in New York City
in 2001 wrote these words that still endure on the beams of their