Ecosystem Trends in the Colorado Rockies

Ecosystem Trends in the Colorado Rockies
		by *Thomas J. Stohlgren* National Biological Service *Jill Baron* National Biological Service *Timothy G.F. Kittel* University Corporation for Atmospheric Research *Dan Brinkley* Colorado State University
Biological conservation is increasingly moving toward an ecosystem and landscape approach, recognizing the prohibitive cost and difficulty of a species-by-species approach (LaRoe 1993). Also, statewide (e.g., Gap Analysis Program) and national surveys (e.g., Environmental Monitoring and Assessment Program or EMAP) are conducted at a scale and level of resolution that do not meet the needs of most small land-management units that require detailed information at the ecosystem and landscape scale (Stohlgren 1994). The Colorado Rockies are an ideal outdoor laboratory for ecosystem science and management. The escalating environmental threats described in this article compelled us to design a landscape-scale assessment of the status and trends of biotic resources.
Our guiding principle is that a strong ecosystem science program provides crucial information for ecosystem management and wise stewardship. We define ecosystem science as the long-term, interdisciplinary study of ecosystem components and processes and their interactions at multiple spatial, temporal, and organizational scales, to meet management needs.
About 76% of the land adjacent to Rocky Mountain National Park is federal land. While the area has not received as much attention as the Greater Yellowstone Ecosystem, there may be as many internal and external threats to the natural resources in the area. The Colorado Rockies are an archetypal ecosystem under siege. Like many national parks, wilderness areas, wildlife refuges, and other natural areas, common threats include encroachment from urbanization and development, habitat fragmentation, fire suppression, nonindigenous species' invasion, and global change (e.g., climate change, bordering land-use changes, and air and water pollution). Since all these threats transcend ownership or stewardship borders, so have interagency concerns for conservation, inventory and monitoring, and research.

Here we identify and quantify trends that threaten ecosystem integrity in Rocky Mountain National Park and the Colorado Rockies. Our specific objectives include presenting qualitative information on vegetation change over the past 65 years, documenting quantitative trends of an ecosystem under siege, showing preliminary results of a long-term global change research program, and discussing the role of ecosystem science in assessing long-term trends in ecosystem condition.

Status and Trends

There is little doubt that the ecosystems of the Colorado Rockies have been altered significantly by humans. The density of ponderosa pine woodlands has increased (Fig. 1) as has suburban development (Veblen and Lorenz 1991). These qualitative changes are supported by qualitative measures (Fig. 2). The response of the forest from turn-of-the-century logging and fires showed a 5-fold increase in ponderosa pine bole (see glossary) biomass. In addition, the human population in Estes Park and the number of visitors in Rocky Mountain National Park have almost doubled since 1960. Urban development throughout the Front Range of Colorado has resulted in increased air pollution. Annual wet deposition values for nitrate, ammonium, and sulfate in the Loch Vale watershed of Rocky Mountain National Park are significantly greater than the average values of 2-4 kg/ha (about 2-4 lb/acre) in remote areas of the world (Fig. 2)

Fig. 1. Drastically increased urbanization in Estes Park/Rocky Mountain National Park, 1921 (above) to 1986 (below). The photographs also show, however, forest recovery from turn-of-the-century logging and human-caused fires (Veblen and Lorenz 1991)..

Elk and moose populations continue to increase in the park (Fig. 2) for many reasons including reduced predation (wolves have been extirpated) and hunting as well as diminished habitat and migratory corridors outside the park. Researchers are now quantifying ungulate (hooved herbivores) habitat relationships and aspen-willow community conservation. Although agricultural land use in Larimer County has declined slightly in recent years (Fig. 2), landscape and ecosystem integrity is challenged by fire suppression, nonindigenous species' invasions, weather modification (i.e., cloud seeding), and global climate change (Stohlgren et al. 1993).

Fig. 2. Trends in Rocky Mountain National Park visitors, agricultural impacts, moose invasion, elk population, forest recovery, air pollution, Estes Park population, and global change in carbon dioxide.

Just as a species-by-species approach to conservation biology is prohibitively expensive, a complex of ecosystem threats cannot be addressed one by one. Our interdisciplinary approach in the Colorado Rockies is based on developing partnerships, consolidating and evaluating the status and trends in existing data, and developing a biogeographical, long-term, multiple spatial-scale monitoring program that fills information gaps and provides a scientific basis for sound ecosystem management. Preliminary results from the National Biological Service global climate change research program show significant interactions of climate, hydrological, and vegetation systems.

Mesoscale (1- to 100-km grids) climate modeling in the Front Range of the Colorado Rockies demonstrated that changes in land cover (e.g,. wild prairie to irrigated agricultural land) can lead to significant and perhaps unexpected changes in mesoscale climate. Computer modeling results indicate that the severity of summer thunderstorms in Rocky Mountain National Park is influenced by spatial patterns in albedo (see glossary) and surface roughness of farmlands several kilometers away (Pielke et al. 1993).
Quantifying trends in mountain hydrology and vegetation change caused by global climate change and assessing the effects of nearby cloud seeding require the development of new predictive models (Baron et al. 1994). Hydrological models are proving effective at estimating stream discharge and regional water supply.
In our long-term forest plots, we found the old-growth spruce and fir forests of the central Rocky Mountains range in biomass from 150,000 to more than 320,000 kg/ha (133,828-285,500 lb/acre) in standing biomass, and annual tree growth remains relatively high in these ancient forests. We are finding that ecotones are sensitive indicators of forest change; the forest-tundra ecotone (transitional area between distinct habitats or ecosystems) in Rocky Mountain National Park has been undergoing substantial directional change for some time (Baker et al. 1994). There is substantial evidence of seedling and sapling invasion within some previously unforested areas within the ecotone, particularly in wet areas in the patch forest zone. This filling in of the ecotone could substantially alter the ecotone environment (Baker et al. 1994). There is little evidence, however, of upward establishment of trees into tundra. To synthesize the vegetation change data, we are developing predictive vegetation change models by using geographic information systems. Our long-term study plots and transects will validate future models.
Implications
This interdisciplinary approach can be widely applied to most U.S. Department of the Interior land units and most ecosystems and will be an essential link to large-scale inventory and monitoring programs (e.g., Gap Analysis Program and EMAP). Ecosystem science is the most logical approach to determine the status and long-term trends of selected resources, populations, and ecosystems. This approach fosters discovery, standardization, linkages, and partnerships as well as coordinated inventory, monitoring, and research. New, standardized sampling protocols are being developed to accurately assess vascular plant species richness, an index of biodiversity (Stohlgren 1994).
		For further information: Thomas J. Stohlgren National Biological Service Rocky Mountain Field Station Natural Resource Ecology Laboratory Colorado State University Fort Collins, CO 80523

References
Baker, W.L., J.J. Honaker, and P.J. Weisberg. 1994. Using aerial photography and GIS to map the forest-tundra ecotone in Rocky Mountain National Park, Colorado, for global change research. Photogrammetric Engineering and Remote Sensing. In press. Baron, J., L. Band, S.W. Running, R.A. Pielke, and T.G.F. Kittel. 1994. Dynamic land surface/atmospheric parameterization at different spatial scales in the Colorado Rocky Mountains. In Proceedings of the Use of Hydrologic Models for Evaluating Climate Change Effects in Snowmelt Water Supply Basins. Agricultural Research Service. In press. LaRoe, E.T. 1993. Implementation of an ecosystem approach to endangered species conservation. Endangered Species Update 10:3-6.	Pielke, R.A., J. Baron, T.Chase, J. Copeland, T.G.F. Kittel, T.J. Lee, R. Walko, X. Zeng. 1993. Use of mesoscale models for simulation of seasonal weather and climate change for the Rocky Mountain states. Proceedings, Second International Conference/Workshop on Integrating GIS and Environmental Modeling. Breckenridge, CO. In press. Stohlgren, T.J. 1994. Planning long-term vegetation studies at landscape scales. In T. M. Powell and J. H. Steele, eds. Ecological time series. Chapman and Hall, New York. In press. Stohlgren, T.J., J. Baron, and T. Kittel. 1993. Understanding coupled climatic, hydrological, and ecosystem responses to global climate change in the Colorado Rockies biogeographical area. Pages 184-200 in W.E. Brown and S.D. Veirs, Jr., eds. Partners in stewardship: Proceedings of the 7th Conference on Research and Resource Management in Parks and on Public Lands. George Wright Society, Hancock, MI. Veblen, T.T., and D.C. Lorenz. 1991. The Colorado Front Range: a century of ecological change. University of Utah Press, Salt Lake City. 186 pp.

References

Baker, W.L., J.J. Honaker, and P.J. Weisberg. 1994. Using aerial photography and GIS to map the forest-tundra ecotone in Rocky Mountain National Park, Colorado, for global change research. Photogrammetric Engineering and Remote Sensing. In press.

Baron, J., L. Band, S.W. Running, R.A. Pielke, and T.G.F. Kittel. 1994. Dynamic land surface/atmospheric parameterization at different spatial scales in the Colorado Rocky Mountains. In Proceedings of the Use of Hydrologic Models for Evaluating Climate Change Effects in Snowmelt Water Supply Basins. Agricultural Research Service. In press.

LaRoe, E.T. 1993. Implementation of an ecosystem approach to endangered species conservation. Endangered Species Update 10:3-6.

Pielke, R.A., J. Baron, T.Chase, J. Copeland, T.G.F. Kittel, T.J. Lee, R. Walko, X. Zeng. 1993. Use of mesoscale models for simulation of seasonal weather and climate change for the Rocky Mountain states. Proceedings, Second International Conference/Workshop on Integrating GIS and Environmental Modeling. Breckenridge, CO. In press.

Stohlgren, T.J. 1994. Planning long-term vegetation studies at landscape scales. In T. M. Powell and J. H. Steele, eds. Ecological time series. Chapman and Hall, New York. In press.

Stohlgren, T.J., J. Baron, and T. Kittel. 1993. Understanding coupled climatic, hydrological, and ecosystem responses to global climate change in the Colorado Rockies biogeographical area. Pages 184-200 in W.E. Brown and S.D. Veirs, Jr., eds. Partners in stewardship: Proceedings of the 7th Conference on Research and Resource Management in Parks and on Public Lands. George Wright Society, Hancock, MI.

Veblen, T.T., and D.C. Lorenz. 1991. The Colorado Front Range: a century of ecological change. University of Utah Press, Salt Lake City. 186 pp.

Ecosystem Trends in the Colorado Rockies

Status and Trends

Implications