Large, old-growth trees are very thinly sprinkled within the redwood forests of the West Coast. BCI-sponsored research shows that these battered old trees offer vital havens where bats and many other wild creatures can nest, roost, and rest.
U.S. Forest Service biologists M.J. Mazurek and William Zielinski estimate that only 3 to 5 percent of the original old-growth redwood forests remain, and these remnants mostly are in patches scattered among much younger forests.
Individual old-growth trees that have survived harvest and such natural forces as fire and flood are considered “legacy trees,” which are much bigger and older than the average trees in the forest. The physical structure of these old trees is much more complex than that of their younger neighbors. And old trees with hollows or cavities, much favored by bats and other wildlife, are becoming extremely rare.
The conservation of old-growth forests and trees, the scientists write, “has received much attention in recent decades, with the heart of the debate focusing on the value of old-growth as habitat for wildlife.”
To confirm that perceived habitat value, Mazurek and Zielinski compared wildlife activity at 30 legacy trees with that at 30 non-legacy trees in Mendocino County, California. The trees were on both public and private land, all of which was being managed for timber production. Monitoring was undertaken in 2001-02 using electronic bat detectors, live traps for small mammals, remote-sensing cameras for larger mammals, and observation surveys for birds. Guano traps were also used in tree hollows and cavities to determine the presence of roosting bats.
The Legacy Tree Project was sponsored by BCI's North American Bat Conservation Partnership.
They found that bat activity was “significantly greater at legacy trees compared to control trees. And every hollow and fire-scarred cavity in the sample revealed evidence of its use by up to four species of bats: big brown bats, California myotis, long-legged myotis, and a fourth species that could not be positively identified from guano.
Twenty-four species of birds and mammals were observed at legacy trees, compared with 10 at the younger trees. And not only were there significantly more species using the legacy trees, a greater number of individuals (primarily birds) used the legacies.
The biologists concluded that, “As measured by species richness, species diversity, and use by a number of different taxa, legacy trees appear to add important habitat value to redwood forests managed for timber.” In terms of conservation planning, they said, this knowledge is extremely valuable.
For example, controlled burning of public forest lands has become a hot topic to help prevent large scale canopy fires. The evidence that fires create cavity habitat for bats and other wildlife supports the idea that fire plays an important role in healthy forest ecosystems.
