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The Real Picture of Sierra Nevada Forests

Book of then-and-now photographs show how region's forests are overgrown.

In April, activists once again criticized efforts to thin forests in the Sierra Nevada, this time because of the inappropriate use of a 1909 Montana photo by the U.S. Forest Service in its brochure, "Forests With a Future."

The photo was used to make a point: historically, California's forests were less dense and more resistant to catastrophic fire. Regrettably, an incorrect photo was used. But that does not change the fact that California's forests were far more fire resistant 100 years ago than they are today.

I have published scores of historic photos side-by-side with modern retakes from the same locations that show how much less dense Sierra Nevada forests were about a hundred years ago.

Our current forest conditions differ greatly with the historic norm - as detailed in my book "Fire in Sierra Nevada Forests: A Photographic Interpretation of Ecological Change Since 1849." California's forests have experienced massive increases in tree cover resulting from human activities, particularly the suppression of natural fires. Similar changes are evident in vegetation throughout the West.

As a wildlife biologist, I know evidence strongly suggests that increasingly dense forests are detrimental to wildlife, including numerous songbirds, rabbits, squirrels, and deer. Historically, wildlife populations adapted to ecosystems that were subjected to frequent low-intensity fires. Today, thicker forests burn in high-intensity crown fires.

Yet, despite this disparity, current conditions often are the primary reference point for biologists making wildlife habitat assessments. We have a tendency, therefore, to essentially preserve wildlife habitat in its present state of decay and high risk of catastrophic wildfire. That must change.

The Forest Service plan for the Sierra Nevada emphasizes retention of forest canopy. To meet the presumed habitat requirements of featured species, Forest Service biologists recommend 50 to 60 percent retention of crown cover. But are high levels of crown closure best? Tree crowns are often so dense that sunlight does not reach the ground and small plants are shaded out.

There is an inverse relationship between the amount of tree cover and the abundance of shrubs, grasses and flowering plants on the forest floor. As trees increase, other green plants decline, primarily from shading and competition for water and nutrients. Wildlife populations also decline because most forest species are dependent not on trees but on low-growing vegetation.

High tree densities and closed canopies pose another threat to wildlife populations: too many trees mean more fuel for catastrophic wildfire.

Scientists from Cal Poly State University and elsewhere have noted that high-intensity wildfire has a far greater impact on the environment than any forest management activities could under California's forestry laws. Catastrophic fires lead to increased erosion, devastate watersheds, pollute the air, and destroy even protected habitat.

The Forest Service has proposed fuel reduction in the Sierra Nevada because it believes that continuing to severely suppress tree harvesting on public lands will increase dramatically the incidence of catastrophic wildfire. With its proposed thinning, the Forest Service expects to reduce the acres lost to catastrophic fire by 30 percent over 50 years and increase the number of old-growth stands.

Yet activists oppose cutting even a miniscule number of trees. The plan they are objecting to calls for harvesting only two tenths of 1 percent of the medium-sized (20-30 inches) trees standing each year. That thinning could save lives and precious habitat.

History can help provide a more accurate view of the natural composition of Northern California landscapes and a more realistic benchmark for understanding the relative condition of wildlife habitat. A historic perspective would also foster a cry to thin forests not just for fire safety, but also for biological diversity.

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Wildlife biologist George E. Gruell is author of Fire in Sierra Nevada Forests: A Photographic Interpretation of Ecological Change Since 1849, (Mountain Press, 2001). The book includes 160 California photos taken from the same spots about one hundred years apart displayed side by side.