Wet and Woody: The Relationship Between Trees and Water in the Lake Champlain Basin

The story of the Lake Champlain watershed cannot be told without trees. Over 70% of the land that drains into the lake is forested, and these forests are deeply connected to the health of our waters. From filtering runoff to storing carbon, trees play an essential role in water quality throughout their lives and long after they die.

Just as trees need water to survive, our waters depend on trees. This relationship is especially important in the areas along streams, rivers, and wetlands where the land and water meet. Trees’ strong woven root structures help keep riverbanks in place, retaining nutrient-laden sediment and preventing erosion. Their roots reduce the amount of stormwater runoff entering waterways while filtering pollutants. During floods, riverside forests allow water to "breathe" across the floodplains instead of rushing downstream, reducing the influx of nutrients that can drive cyanobacteria blooms.

In forested communities, living trees are food, houses, air purifiers, roads, playgrounds, backscratchers, shade sources, beds, and refuge for a wide variety of species. Yet a tree’s life does not end in death. Decaying trees teem with biological activity, making way for new life. Snags, or standing dead and dying trees, host a diversity of invertebrates in their tissues. The softened wood allows woodpeckers and other cavity nesters to bore a hole and make a home. Once abandoned, these cavities host a wider array of other wildlife looking for a place to move in. Some species, including wood ducks and bluebirds, evolved to nest in snag cavities and depend on them for survival.

If a tree falls in the woods and no one is there to hear it, does it make a sound? Ecologists may ask a different question: where does it land? When wood hits the water, it continues to benefit natural communities, both terrestrial and aquatic. For land dwellers, these fallen trunks and branches expand access to territory and create new vantage points, serving as natural bridges, sunny basking areas, and natural perches. Underwater, the wood allows pockets of sediment to accrue upstream. Fish benefit from these little bumps and valleys, using them as spawning habitat and taking a rest or a snack in the adjacent pools. The submerged wood provides a place for algae to grow, generating dissolved oxygen and providing a food source for a wide assortment of aquatic invertebrates. 

Large woody debris also helps a stream function more naturally during high-water events. Fallen trees break up the streambank, slowing higher flows and capturing sediments rather than letting them wash downstream into the lake. When logs span across the stream toward a floodplain, they can redirect water and pollutants into surrounding soils where it can be absorbed rather than washed downstream. 

Research from the University of Vermont highlighted another important role for soggy logs: carbon storage. In freshwater ecosystems, submerged wood decomposes much more slowly than wood on land. Fungi, the main decomposers of terrestrial wood, cannot survive the low-oxygen environments inside of wet wood. Instead, bacteria will break it down, but it is limited to a thin layer on the wood’s surface rather than working throughout the gaps in the interior. For large trees with low surface-area-to-volume ratios, there is even less space for bacteria to work relative to the size of the piece. As a result, trees in streams—particularly large ones—release carbon much more slowly than snags do, making them valuable carbon sinks.