Mature and old-growth forests and trees provide diverse habitat for wildlife and vegetation to a degree that younger forests cannot. Older trees develop unique features that support complex habitats, often serving as biodiversity hotspots. Mature forests are far less prevalent across the U.S. than they once were and are the increasingly scarce preferred habitat for a myriad of imperiled species. Conversely, relative to mature forests, there is generally no shortage of young forests, undermining justifications for logging to convert mature stands to an earlier successional state. Logging of mature and old-growth trees in the United States removes these remaining cornerstones of ecosystem integrity, compounding the ongoing biodiversity crisis.
As forests age over decades and centuries, they form complex ecosystems with vibrant living trees at their foundation. Natural disturbances create openings for younger trees within mature forests, adding complexity not well replicated through logging practices. Left to develop, older forests can create cool shady microclimates due to high levels of canopy closure and evapotranspiration through larger leaves, nurturing a variety of plants and wildlife that would often struggle to survive elsewhere. These benefits do not end once a tree dies. Older forests also have a variety of dead trees, including standing logs (snags)—which are important habitat elements for numerous woodpeckers, owls, and rodents—and fallen large logs (coarse woody debris)—which provide food foraging for bears, habitat and cover for rodents, and essential nutrients for new vegetation and tree saplings. As a result of these and other features, mature and old growth forests and trees provide irreplaceable regional climate refugia for a wide variety of threatened, endangered, and sensitive species in the U.S. including the spotted owl, marbled murrelet, Kaibab squirrel, Canada lynx, fisher, pacific marten, northern long eared bat, and many others.
Similarly, mature forests interact with other landscape features to enhance biodiversity as bigger, older trees play an important part in hydrological cycles. Mature and old-growth forests often include riparian zones and critical floodplains, which help to regulate water temperature, provide critical inputs of woody debris, and stabilize streambanks. These zones provide water for a range of fish and wildlife as well as cool, moist growing conditions for many vegetative species. All of these ecosystem components are interconnected and rely on the critical foundation of mature and old growth forests to sustain irreplaceable biodiversity.
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