Applied Historical Ecology
Applied historical ecology is the use of historical knowledge in the management of ecosystems. Historical perspectives increase our understanding of the dynamic nature of landscapes and provide a frame of reference for assessing modern patterns and processes. Historical timeframes range from decades to millennia. As Aldo Leopold (1941) observed, "A science of land health needs, first of all, a base datum of normality, a picture of how healthy land maintains itself as an organism."
Historical ecology encompasses all of the data, techniques, and perspectives from paleoecology; land-use history from archival and documentary research; and long-term ecological research and monitoring extended over decades. Multiple, comparative histories from many locations can help evaluate both cultural and natural causes of variability and characterize the overall dynamic properties of ecosystems (Swetnam et al. 1999).
In fact, twentieth-century trends suggest that disregarding history can be perilous. Examples include the emergence of increasingly severe wildfire activity in the western United States and the role of extreme drought in triggering forest dieback and accelerated soil erosion in the American Southwest.
Human-generated changes must be constrained because nature has functional, historical, and evolutionary limits. Nature has a range of ways to be, but there is a limit to those ways, and, therefore, human changes must be within those limits (Christensen et al. 1996).
A primary objective of historical ecology is to help define the various limits, the natural range of variability for ecological systems (Swetnam et al. 1999). In this way, applying historical knowledge guides and constrains resource management actions to sustainably mesh with those limits.
Environmental history research concentrates on the patterns and causes of ecological changes in the landscapes of these southwestern mountain ranges. It includes extensive work on historic, ground-based photographs for this area, with relocation and retaking of photographs that were taken as long ago as 1880 by the Bureau of Biological Survey, U.S. Geological Survey, USDA Forest Service, early archaeologists, and others.
For example, Figure 1 shows paired photographs of an area in the present-day Valles Caldera National Preserve. In the September 1997 retake photograph at right, notable changes include the downslope expansion of blue spruce into meadow margins and increased forest densities, along with much healthier range conditions. Note the rocks and soil exposed in the foreground of the 1906 original at left, likely due primarily to livestock grazing and trampling, although deposition of sediment from the small ephemeral drainage visible in this view might have contributed to the raw look of this site. In contrast, the 1997 view depicts the lush growth of grass possible with the more sustainable range management practices employed by more recent owners, including the exclusion of sheep, lower stocking rates, and herd rotation. The 1906 view shows barren stream margins and banks along the stream, while the stream is obscured by vegetation in the modern view.
|The Valles Caldera National Preserve|
|Figure 1. A paired photograph example. (Left) View to the southeast taken by Vernon Bailey (of the U.S. Bureau of Biological Survey) in August 1906 along Valle San Antonio in what is today the Valles Caldera National Preserve. (Right) The September 1997 retake. view full-sized images|
These and other old photographs confirm tree-ring data that the vegetation of the American Southwest has been greatly altered by over a century of livestock grazing and fire suppression, with a shift in dominance from grassy vegetation to denser and more extensive forests and woodlands (Allen 1998). Such information is being used to help guide ecosystem restoration efforts in the region (see Forest and Woodland Restoration in the Southwest).
Changes observed in time sequences of aerial photographs extending back to 1935 have been used to map significant changes in landscape patterns in the Jemez Mountains of New Mexico. One prominent change was the rapid shift of the forest/woodland ecotone upslope by as much as 2 km between 1954 and 1958 (Figure 2), due to the death of drought-stressed ponderosa pine trees (Allen and Breshears 1998).
This kind of information, developed using historical ecology approaches, provides perspectives on the potential ecological effects of global climate changes. Historic data show that extreme droughts can drive major disturbances such as forest dieback, fire, and soil erosion that can lead to large, rapid carbon losses. Given the likely feedbacks to global climate changes, carbon management plans should include explicit strategies to mitigate carbon losses to maintain current land stocks of global carbon and minimize further terrestrial losses. It is important to better understand and predict the potential for rapid, disturbance-induced (fire, drought) carbon losses and integrate this knowledge into sound, sustainable policy options to mitigate possible global climate change effects.
Resources and References
Allen, C.D. 1994. Ecological perspective: Linking ecology, GIS, and remote sensing to ecosystem management. Pages 111-139 in V.A. Sample (ed.). Remote sensing and GIS in ecosystem management. Island Press, Covelo, CA.
Allen, C.D. 1998. A ponderosa pine natural area reveals its secrets. Pages 551-552 in M.J. Mac, P.A. Opler, C.E. Puckett Haecker, and P.D. Doran (eds). Status and trends of the nation's biological resources. Vol. 2. U.S. Department of the Interior, U.S. Geological Survey, Reston, VA.
Allen, C.D., J.L. Betancourt, and T.W. Swetnam. 1998. Landscape changes in the southwestern United States: Techniques, long-term data sets, and trends. Pages 71-84 in T.D. Sisk (ed.). Perspectives on the land use history of North America: A context for understanding our changing environment. U.S. Geological Survey, Biological Science Report USGS/BRD/BSR-1998-0003.
Allen, C.D., and D.D. Breshears. 1998. Drought-induced shift of a forest-woodland ecotone: Rapid landscape response to climate variation. Proceedings of the National Academy of Sciences 95:14839-14842.
Breshears, D.D., and C.D. Allen. 2002. The importance of rapid, disturbance-induced losses in carbon management and sequestration. Global Ecology and Biogeography Letters 11(1):1-15.
Christensen, N.L., et al. 1996. The report of the Ecological Society of America committee on the scientific basis for ecosystem management. Ecological Applications 6:665-691.
Crumley, Carole L. (ed.). 1993. Historical ecology: Cultural knowledge and changing landscapes. Santa Fe, NM: School of
American Research Press, Seattle. Distributed by the University of Washington Press.
Egan, D. and E.A. Howell (ed.). 2001.The Historical ecology handbook: A restorationist's guide to reference ecosystems. Island Press, Washington, D.C.
Leopold, A. 1941. Wilderness as a land laboratory. Living Wilderness 6:3.
Swetnam, T.W., C.D. Allen, and J. Betancourt. 1999. Applied historical ecology: Using the past to manage for the future. Ecological Applications 9(4):1189-1206.