Vegetation Survey and Preliminary Ecological Assessment of Valles Caldera National Preserve, New Mexico.

摘要

With the acquisition of the Valles Caldera National Preserve (VCNP) has come the need for comprehensive biological inventories to support sound natural resources management. Fundamental components of this effort are the development of a vegetation map and associated vegetation community classification, and a preliminary assessment of the condition and regional status of these communities. Accordingly, we conducted an initial vegetation survey to help characterize the range of variation and condition among the preserves ecosystems and to provide a foundation for the development of a high-resolution vegetation map to be used in planning and management. In 2001, we established 100 vegetation plots in the preserves forests and grasslands that have detailed species inventories, site and tree stand characterizations, and repeat photo points. In this first year, sampling was focused on describing reference conditions in stands that had the fewest impacts from past logging and grazing or those with special biological elements. Data from these plots were used to develop a vegetation classification that conforms to the National Vegetation Classification system standards. The classification serves as an organizing tool for information on the preserves ecosystems and for defining map units for a vegetation map to be developed in succeeding years. We identified and described 65 plant associations that encompass high elevation sub-alpine forests, down through mixed conifer to open foothill pine woodlands, and from high montane grasslands to valley floor wetlands. This makes VCNP one the most diverse sites in the Southern Rocky Mountains Ecoregion (southern Wyoming to northern New Mexico). The montane grasslands and wetlands of the preserve are of particular importance because they are considered part of an ecosystem type that is threatened and declining on a global basis due to the impacts of grazing and development. The estimated 26,000 acres of montane grasslands along with the 1,650 acres of wetlands on the preserve represent some of the largest and highest quality occurrences in terms of ecological function and biodiversity within the ecoregion, and they potentially represent a 20% increase in acreage of montane grasslands and wetlands under protection in parks and preserves. Although of relatively high quality, long-term cattle and sheep grazing has left an imprint on these communities in terms of declines in native bunchgrasses and increases in exotic or undesirable species. These effects are further confounded by the presence of sizable elk populations on the preserve. Furthermore, past grazing impacts are also thought to be responsible for declines in aquatic habitat and the cold-water fishery within the preserve. Given this complexity, the implementation and maintenance of a scientific monitoring program that addresses the interactions among grazers and ecological processes such as fire and flooding, is critical to the restoration and long-term sustainability of these grassland and associated aquatic ecosystems.