Progressing Toward a Standardized Classification of Vegetation for the U.S.
Michael D. Jennings
Since 1989, GAP land cover mappers have been in the unenviable position of applying a vegetation classification system before it was well developed. During this time, GAP funded The Nature Conservancy (TNC) regional ecologists to produce first-ever regional classifications of alliance vegetation types. These classifications are now complete for the Northeast (Sneddon et al. 1994), Southeast (Weakley et al. 1997), and Midwest (Drake and Faber-Langendoen 1997). The Western region classification (Bourgeron and Engelking 1994) is being redone by Marion Reid and colleagues (TNC Western Regional Office) to provide full descriptions of each alliance, including California as well.
In Bulletin No. 5, I reported the establishment of the Ecological Society of Americas Vegetation Classification Panel (ESA-Veg.). The panels mission is to provide a standardized, scientifically credible classification of vegetation for the U.S. in partnership with TNC and the Federal Geographic Data Committee (FGDC). This article provides a bit more background about vegetation classification in the U.S. and an overview of the ESA-Veg. status. Some of the following is based on material from a draft ESA-Veg. manuscript discussed below.
Today, the United States is close to having its first fully functional, widely applied vegetation classification, that, based on the tradition of systematics, will be improved upon as our knowledge expands. On October 22 of this year, the Secretary of the Interior, acting as Chair of the FGDC, gave final approval to the Vegetation Information and Classification Standard (FGDC 1997). This is now the standard vegetation classification for U.S. federal agencies and their cooperators. Those already familiar with the classification will recall its two-part structure of classifying vegetation by physical and environmental attributes in one part and by floristic assemblage in the other part (Table 1). While the FGDCs "Vegetation Information and Classification Standard" includes a full classification of the physiognomic part, it only describes the floristic classification in concept because this part of the classification is far from being fully developed and requires a very large effort (Loucks 1996).
The ESA has joined with TNC, federal agencies, and others to meet the need for a unified floristically-based classification for the U.S. The intent is in strengthening the existing classification system by providing a mechanism for its refinement through scientific review and by disseminating its standards. These objectives are being accomplished in phases, with the initial focus having been on review and improvement of the original FGDC proposal. The second phase, now in progress, is to provide the basic standards needed to support a floristically-based classification. In addition, a framework for ongoing review of the described types and the systems structure is needed, both initially and as changes are proposed. The common purpose is to provide a recognized vegetation classification system of broad utility for incorporating ecological science in conservation, natural resource management, planning, and research.
Recent History of Vegetation Classification in the U.S.
The United States was late to recognize the need for a unified national vegetation classification. As early as 1973, international scientists working for the United Nations Educational Scientific Cultural Organization developed and adopted a worldwide vegetation classification system based largely on physiognomy (UNESCO 1973). Many countries also had successful vegetation classifications completed or under way (Rodwell et al. 1995). The UNESCO system was not generally adopted in the United States because it was perceived as being not detailed enough to be useful at a local level. At that time, there was little recognition of the parallel importance of regional context with localized content, and the value of a single national classification system was not acknowledged. Some federal land management agencies produced vegetation classifications, maps, and other information about public lands that they administered, but these projects typically were limited in scope and geography (Ellis et al. 1977).
In the late 1970s, TNC initiated state natural heritage programs. Inventories of rare species and community "element occurrences" were produced as part of state agency surveys, and some state-specific community classification systems were developed. Although many state natural heritage programs began collecting descriptions of plant communities by the early 1980s, the development of state-level classifications was not widespread until the mid-1990s, driven largely by a coordinated effort to map existing vegetation.
In the early 1980s, five federal agencies tried to develop a national classification system integrating vegetation, soils, water, and landform (Driscoll et al. 1984). The vegetation criteria were based on a potential taxonomic hierarchy. One obstacle was identifying potential vegetation types for inventory sites when taxonomies and keys for the floristic-based levels were available for only a few regions in the country. A second obstacle was that the system was designed primarily for aggregating plot data; little attention was paid to mapping systems and methods for mapping land cover. Third, the classification could deal only with potential, not existing, vegetation.
In the late 1980s, the U.S. Fish and Wildlife Service initiated a research project that became the National Gap Analysis Program (GAP). In 1990, GAP began supporting TNCs effort to develop a national system (Jennings 1993) which started by compiling and standardizing regional (multistate) classifications from state natural heritage programs. Supported by GAP and the National Park Vegetation Mapping Program, Grossman et al. (1994) drafted the basis for what is now recognized as the National Vegetation Classification (NVC).
The requirement for national spatial information standards, including vegetation, was implemented by the federal government with the 1990 revised Office of Management and Budget Circular A-16, Coordination of Surveying, Mapping, and Related Spatial Data Activities. The goals of this circular were to develop the National Spatial Data Infrastructure (NSDI), to reduce duplication, to reduce the expense of developing new geographically based data, and to increase the benefits of using available data through coordination and standardization of federal geographic data. The circular established the Federal Geographic Data Committee (FGDC) to promote development of distributed database systems, information standards, exchange formats, and guidelines, and to encourage broad public access.
Interagency commitment to coordination under Circular A-16 was strengthened in 1994 under Executive Order 12906, Coordinating Geographic Data Acquisition and Access: the National Spatial Data Infrastructure. It instructed the FGDC to involve state, local, and tribal governments in development, and to use the expertise of academia, the private sector, and professional societies in implementing the order. Under this mandate, the FGDC established a subcommittee to develop standards for mapping vegetation.
The ESA established its Panel on Vegetation Classification in 1994 (Barbour 1994, Peet 1994, Loucks 1995, 1996), and the panel began by reviewing the draft FGDC Vegetation Classification and Information Standards. Completion of the review and publication of the FGDC proposed national classification (the overall framework and details for physiognomic levels; see http://www.fgdc.gov/Standards/Status/sub2_1.html ) concluded the first phase of the ESA Panels work. However, the bulk of the ESA panels work is to deal with the issues of a floristically defined vegetation classification. This is the focus of the second phase of the ESA Panels activities.
A Point of Departure
An early step in the ongoing cooperative process to develop a national vegetation classification is to recognize the present baseline classification as a point of departure. This must be followed by recommended standards that both require and provide a mechanism for further improvements and complete documentation of named units. To improve these standards, work groups will be established, composed of academic, agency, and private-sector scientists.
Both TNCs classification (Nature Conservancy Ecology Working Group 1997) and the FGDC Vegetation Classification and Information Standards must now be recognized as a single, integrated system. A complete review of the floristic levels is required, but a consensus on basic standards is needed first. In August of this year, the ESA panel distributed for review a draft version of An Initiative for a Standardized Classification of Vegetation in the United States. This document proposes the first approximation of standards for the categories shown in Table 2. These standards lay the foundation for an enduring taxonomy of vegetation that can be improved upon, in a collaborative way, as our body of knowledge expands.
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