Old-growth Forests of the Sierra Nevada
"As we liquidate the ancient forests, we are redesigning the forests of the future. In fact, we are redesigning the entire world, and we are simultaneously throwing away Nature's blueprint." - Chris Maser, forest ecologist
There are a variety of definitions for old-growth forests, but they are generally defined as forests in their later stages of development, usually referred to as late-seral or late successional. Approximately 4 million acres of old-growth are remaining in the Sierra Nevada, however most of the remaining stands have been highly fragmented, with the majority of old growth found only in the highest reaches of the mountains, wilderness reserves in the lower alpine zone, or in steep inaccessible stream canyons.
Trees sizes for old-growth have been variously defined as trees over 24" diameter with medium to high canopy cover, to 30" trees; however age is the most important factor, and some ancient trees may not appear huge in girth. Old growth trees are - at the minimum - 150-200 years in age. Tree size and age-related structure are a result of growing conditions, species type, elevation, and climatic conditions resulting from the diversity of ecosystems in the Sierra Nevada.
There has been an alarming decline in old-growth forest acres and structure in the Sierra Nevada since the 1850's. Estimates vary on the amount of old-growth that existed in the pre-settlement era, depending on what time period is considered. The best estimate (SNEP 1996) states that formerly, late-successional habitat occupied roughly 67% of the mixed conifer forest landscape. Today, it is estimated that only 12% of mixed conifer old-growth forest remains, a staggering loss of approximately 82% of the historical acreage of old-growth found in mixed conifer forests.
Much of this loss is from the high-grading (a type of selective cutting where some or all of the biggest and best trees are cut) of large trees, railroad logging, and clear cutting logging practices, which continued up to the early 1990's on Federal land and continue today on industrial timber lands in the Sierra Nevada. During the logging "hey-days" of the 1980's the Forest Service was producing over 1 billion board feet of saw-timber annually from the Sierra Nevada, much of it in large old-growth trees.
Timber industrial giant Sierra Pacific Industries continues to liquidate all of their remaining old growth trees in their ownership, throughout the Sierra Nevada on the western slope. After clearcutting, the industrial practice is to farm the forest, planting trees that will be uniformly managed with herbicides and then cut again after 50 to 80 years, starting the cycle over again. This is called the timber "rotation." These practices make preservation of the remaining old forest stands in public ownership - on national forest lands - all the more critical.
Old-growth forests can play a significant role in storing carbon and helping to mitigate global warming. Old-growth forests in the Northern Hemisphere sequester ten percent of the world's net ecosystem productivity, or NEP, a measure of carbon sequestered. Their value in maintaining a climate that can sustain life far outweighs the short term economic gain from cutting them down for lumber.
Old-growth trees provide a critical habitat structural component of species like the imperiled California spotted owl. A study of California spotted owl nest locations in the southern Sierra Nevada (North 2000) found the mean age of nest trees to be >225 years. Old trees develop important characteristics such as cavities and broken tops, which provide ideal and integral nest sites. Also, the large canopies often found in old-growth stands provide much needed shade in hot summer weather for the heat sensitive spotted owl.
Other imperiled species in the Sierra Nevada that depend on intact old-growth habitat are the Northern flying squirrel, Pacific fisher, and pileated woodpecker. Continued degradation of the remaining old-growth in the Sierra Nevada will likewise continue to put pressure on these threatened wildlife species.
Many rare plants, fungi, bryophytes and lichens are also associated with old forests. Some may take decades to build up complex symbiotic relationships with their conifer hosts before they become established and reproduce. Some examples include a suite of terrestrial orchids including coral root, lady slipper, and rattlesnake plantain. Very little is known about the life histories or ecology of some of these rarely seen forest species.
The original 2001 Sierra Nevada Framework Plan called for 4.2 million acres of old forest emphasis areas with specific goals of protecting and enhancing old-growth forests. The 2004 revisions to the Framework allow intensive harvesting of 20"-30" trees in 75% of the old-growth reserves across the Sierra Nevada.
Ansley, J-A.S., and J.J. Battles. 1998. Forest Composition, Structure and Change in an Old-growth Mixed Conifer Forest in the Northern Sierra Nevada. Journal of the Torrey Botanical Society, 125(4) 297-308. (418KB PDF)
Aubry, K.B., C.B. Halpern, and C.E. Peterson. In Press 2009. Variable-retention harvests
in the Pacific Northwest: a review of short-term findings from the DEMO study. Forest
Ecology and Management. (595 KB PDF)
Franklin, J.F., and J.A. Fites-Kaufmann. 1996. Assessment of Late-Successional Forests of the Sierra Nevada. Sierra Nevada Ecosystem Project: Final report to Congress, vol. II, Assessments and scientific basis for management options. Davis: University of California, Centers for Water and Wildland Resources, 1996. Large file in four parts: Part 1 (3 MB), Part 2 (4.71 MB) Part 3 (1.57 MB) Part 4 (2.95 MB)
Warbington, R., and D. Beardsley. 2002. 2002 Estimates of Old Growth Forests on the 18 National Forests of the Pacific Southwest Region. US Department of Agriculture, Forest Service, Pacific Southwest Region. (2.94MB PDF)
Wilson, J.S., and P.J. Baker. 1998. Mitigating Fire Risk to Late-successional Forest Reserves on the East Slope of the Washington Cascade Range, USA. Forest Ecology and Management 110, 59-75. (816KB PDF)