Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

Rarity of species and ecosystems is a common conservation criterion, but in measuring risk, rarity may be less relevant than extent of historical decline or potential for further decline. Many rare species and communities have apparently always been rare and may not be highly vulnerable to extinction. On the other hand, a major decline in a once-dominant or widespread species or ecosystem type may have ecological consequences far more severe than the loss of the last few individuals of a chronically rare species or the loss of a plant community that never covered more than a small area.

This indicator will be based on an identification of forest community types that occupy at least 70% fewer acres than at presettlement. Note that the “forest community types” described in this indicator are more specific than the groupings described in Forest Types. The “forest types” reported in that indicator are broad classifications, each of which would include many “forest community types.”

The indicator will report the number of these community types and the present acreage of the suite of significantly reduced community types. It will also report the change in area of these community types from one reporting period to the next, allowing readers to understand whether reductions in the area of these already-reduced types is continuing or has been stopped or reversed.

Note that use of a presettlement baseline is not intended to imply that forest community types were “pristine” or completely unaffected by human activity. It is clear that Indians exerted influence over the presettlement landscape, although the extent of that influence is currently under debate and is likely to have differed by region. The use of a presettlement baseline is also not intended to serve as a goal for action or policy. Rather, it is intended as a relatively long-term reference point, against which to compare current conditions.

A recent review of threats to imperiled species in the United States found that 85% of all imperiled species were threatened by habitat degradation or loss (including 92% of vertebrates, 87% of invertebrates, and 81% of plants) (Wilcove et al. 1998). A separate study tallied species that were listed or were candidates for listing under the Endangered Species Act (ESA) for three major endangered ecosystems. As an example, in 1993 the longleaf pine–wiregrass ecosystem, which has declined by nearly 99% since presettlement times, contained 27 ESA-listed species and 99 species that were candidates or proposed for listing under ESA (Noss et al. 1995).

Forest community types for this indicator are defined at the “alliance” level of the National Vegetation Classification System (Grossman et al. 1998). An alliance is a group of plant associations that share a similar architecture and one or more diagnostic species, which are generally the dominants in the primary canopy. In some cases, aggregations of ecologically related alliances may be tracked. The alliance level of classification is roughly equivalent to “cover type” as defined by the Society of American Foresters.

Ecosystems can decline in area through outright conversion to another land cover or through gradual changes, like those that accompany fire suppression, which allows other species to take over a forest. For this indicator, as long as an area has the characteristics of a specific forest community type, it would be counted as part of that type. If, for example, significant vegetation changes occurred as a result of fire suppression, the forest may eventually be classified as a different type.

The Data Gap

The NatureServe Information and the USDA Forest Service Forest Inventory and Analysis (FIA) program are collaborating on development of methods that would allow estimation of the area of alliances (or in certain cases, aggregations of alliances) from existing FIA data. This would provide a recent historical perspective on changes in alliance area, and would allow the area of these community types to be tracked in the future.

Many scientists recognize the value of developing a national map of presettlement vegetation at the alliance or comparable level to provide a more quantitative basis for the assessment of forest cover change. A preliminary approach to this analysis could be done by crosswalking alliances to the Kuchler Potential Natural Vegetation types (Kuchler 1964). The NatureServe Information is seeking funding to complete this work.

Specific data in the indicator writeup are from sources as follows. Data on redwood acreage and Great Lakes pine forest are from Klopatek et al. 1979 and Powell et al. 1993. It is important to note that other estimates exist for the reduction in acreage of redwood (see Noss 1995) and Great Lakes pine forest (see Frelich 1995). Data on oak savanna are from Nuzzo 1986.

References

Eyre F. H. et al. 1980. Forest cover types of the United States. Washington, DC. Society of American Foresters.

Frelich, L. 1995. Old forest in the Lake states today and before European settlement. Natural Areas Journal 15:157–167.

Grossman, D.H., et al. 1998. International classification of ecological communities: Terrestrial vegetation of the United States. Volume I: The national vegetation classification standard. Arlington, VA. The Nature Conservancy. http://www.natureserve.org/publications/icec/toc1.html.

Klopatek, J.M., R.J. Olson, C.J. Emerson, and J.L. Jones. 1979. Land-use conflicts with natural vegetation in the United States. Environmental Conservation 6:191–199.

Kuchler, A.W. 1964. Manual to accompany the map: Potential natural vegetation of the conterminous United States. Special Publication 36, American Geographical Society, New York.

Noss, R.F., E.T. LaRoe, and J.M. Scott. 1995. Endangered ecosystems of the United States: A preliminary assessment of loss and degradation. U.S. Geological Survey, Biological Report No. 28.

Nuzzo, V.A. 1986. Extent and status of Midwest oaks savanna: Presettlement and 1985. Natural Areas Journal 6(2):6–36.

Powell, D.S., J.L. Faulkner, D.R. Darr, Z. Zhu, and D.W. MacCleery. 1993. Forest resources of the United States, 1992. General Technical Report RM-234. Fort Collins, CO: USDA Forest Service, Rocky Mountain Forest and Range Experiment Station. Revised, June 1994.

Wilcove, D.S., et al. 1998. Quantifying threats to imperiled species in the United States. BioScience 48:607–615.