Why Protecting Old Growth Trees Protect Our Fish and Waters Too

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by Helena Virga. Forest and Climate Campaign, Oregon Wild

Oregon’s native trout, steelhead, and salmon rely on our trees, and our trees rely on our fish. Over millions of years, many plants and animals of the Pacific Northwest evolved to rely on the nutrient exchanges brought by salmon and steelhead returning from the ocean to spawn. In order for these fish to grow and thrive, they need an abundance of food from the sea. The nutrition gained from their years in the ocean allows them to successfully return to their home waters to spawn.

When these fish return, they bring with them an abundance of nutrients from the ocean. When salmon (and sometimes steelhead) die, they provide nutrients, including nitrogen and phosphorus to the river and its vegetation. According to Robert Naiman of the University of Washington, vegetation alongside streams gets just under 25% of its nitrogen from salmon. Other researchers report up to 70% of the nitrogen found in riparian zones comes from salmon. Some of these nutrients sustain streamside trees like alder and willows, but it is also an important source of nutrients for our old-growth giants, the douglas fir, red cedar, and sitka spruce that define our region.

The link between tree size and salmon runs are intertwined, and just as much as the trees need salmon, salmon need the trees as well.

Large trees keep streams cool for spawning, falling leaves, branches, and trunks provide resting pools, covr habitat, and food for the fish. Tree roots slow erosion by stabilizing banks and anchoring the soil on steep slopes. Healthy, mature forest ecosystems also help shade the rivers and streams, reducing temperature, and moderate the effects of drought. Finally, mature and old-growth forests are important for combating climate change. Trees are the most efficient technology ever invented for capturing and storing carbon dioxide, and the bigger they get, the more they hold. An old-growth douglas fir can capture and store hundreds of thousands of pounds of carbon dioxide, and keep it out of our atmosphere for centuries.

When these mature and old-growth forests are logged, it can lead to serious soil erosion and mudslides, poor water quality, and degraded habitat. Dense young tree plantations, which provide little shade but consume enormous amounts of water, can reduce flows in nearby streams and rivers. Overall, intact healthy forests contribute to healthy watersheds, which will be especially valuable as the impacts of climate change, such as drought and heatwaves, become more severe. When old-growth is logged, most of the carbon once stored in the tree is quickly lost back into our atmosphere. The loss of our historic mature and old-growth forests has been a major factor in the decline of our native trout, salmon, and steelhead, particularly in the Oregon Cascades and Coast Range.

Oregon Wild’s Climate Forest Campaign is fighting to protect our remaining mature and old growth trees on public lands, and to defend our forests and our waters from abusive logging practices. We are partnering with organizations from Alaska to North Carolina to urge President Biden to establish stronger, permanent protections for America’s mature and old-growth forests as a way to both combat climate change, and protect the vital habitat and clean water they provide. Take action by filling in this form here to tell the The Forest Service and Bureau of Land Management why our climate forests are worth more standing.

You can also support this campaign by signing your organization on to support by emailing us at info@climate-forests.org, and following our campaign on social media.

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