An Ode to the Cottonwood
It’s fall and the Elk Valley is painted a shining golden hue. As cottonwood trees prepare for winter, they lose their green chlorophyll leaving only the yellow/orange “carotenoid” pigments behind. Just weeks ago, the dense canopy of these towering giants cast a deep shadow; a welcome respite from the summer heat. A few months prior–in the springtime–their seeds meandered like snowflakes to the ground. Cottonwoods, and specifically black cottonwoods (Populus trichocarpa), are an emblematic tree species in the Elk Valley. Identifiable by their rugged grey bark and drop-shaped leaves, cottonwood trees typically have a lifespan of no more than 100-200 years; however, visitors to the Ancient Cottonwood Trail (Morrissey area), will witness trees aged up to 400 years old–the oldest known in the world. These trees decrease flood impacts, provide a home and harbour for Elk Valley animals, and define our streamside ecosystems.
Slowing Floodwaters
Favouring wet conditions, cottonwoods thrive along streams, lakes, and floodplains throughout the Elk Valley bottom. As the river meanders, cottonwood seedlings are some of the first to burst through the exposed gravel and form dense patches of saplings. During floods, their pliable stems withstand fast moving water, slowing it down and forcing it to absorb into the ground and return to the stream. Slower flood waters, as one might expect, cause less damage as they ravage through urban areas.
As they grow older, cottonwood roots interlace the earth. Anyone who has floated along the river and looked at overhanging riverbanks has noticed dense root systems holding onto loose soil and rocks. In
this way, the roots act as a natural rebar, slowing down erosion of riverside lands. In many urban areas a widely practised method of flood and erosion mitigation is riprap. Large boulders or artificial materials are lined along the riverbank and prevent floodwaters from washing away the valuable property. While it might be structurally effective, this kind of prevention misses out on many advantages of shoreline trees–namely, their value as a home for fish and wildlife.
A Home for Fish and Wildlife
Countless terrestrial wildlife species make cottonwood trees their home. Large mammals, including elk, grizzly bears, and moose, hide from the summer sun and munch on the understory plants carpeting cottonwood stands. Birds build their homes amongst the branches, and beavers use the soft wood as construction materials. But streamside forests are vital for fish too. Overhanging branches cast a shadow, decreasing water temperature by an average of 5C. For fish like trout, this is a make-or-break kind of difference. Being cold blooded, fish don’t regulate their temperature and rely on the temperature of their environment for metabolic processes. Temperature extremes are therefore one of the greatest stressors, and expected to be even greater with climate change. At water temperatures above 20C fish become heat-stressed, and temperatures exceeding 25C can quickly cause death. Of the many complex actions needed to improve fish habitat, restoring streamside vegetation is one of the simplest.
Restoring Cottonwood Forests
Cottonwood trees were often removed for agriculture and development in stream adjacent areas throughout the Elk Valley. This fall, the Elk River Alliance is breaking ground on a multiyear cottonwood restoration project. Over the next four years, ERA aims to plant 20,000 cottonwood live-stakes across four conservation areas in the valley. This effort would not be possible without amazing community volunteers who assist with live-stake collection and planting. If you’re still reading this, odds are you’re interested in conservation, and we urge you to participate in the effort. To learn more, please visit elkriveralliance.ca or email info@elkriveralliance.ca.