Energy Considerations: The Flow Of Life Through The River

Stream-side Foliage And Its Role In Stream Ecology

Leaves accumlate 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 hours.

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 pioneer 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 essential nutrients (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 art salon:

	The Leaf
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