Proposed forest management of the Mount Emily Recreation Area has raised important questions about large trees. I’m an ecologist who studies forest ecosystems and the significant values they provide. I’d like to share a few findings specific to the largest trees in the forest that underscore their outsized benefits to both the forest and local community.

Large trees are crucial in ecosystem water and energy cycles. Large deeply rooted trees tap groundwater resources not available to shallow-rooted plants. During drier months roots lift deep soil water up to shallow, drier portions of soil and release it, sharing water to the ecosystem, including neighboring plants of different species. A study in old growth ponderosa pine found that during July and August this process accounted for approximately 35% of total daily water usage from the upper soil, adding weeks of water during drought. This allows the ecosystem to continue photosynthesis, storing more carbon, and cooling the forest canopy as water evaporates from foliage. Forest canopies can register summer surface temperatures more than 30°F cooler than adjacent non-forest cover types, and large trees are the engine of this work. The water released to the atmosphere contributes to downwind moisture content and rainfall. Intact forests with large trees are positively associated with cool summer temperatures, increased late-summer streamflow and clean surface drinking water.

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David Mildrexler is a systems ecologist with Eastern Oregon Legacy Lands where he focuses on terrestrial systems science, large landscape conservation, and the educational programs at Wallowology Natural History Discovery Center. He holds an M.S. in forest science from the University of Montana, and a PhD in forest ecosystems and society from Oregon State University.

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