Terrestrial Vegetation Of The United States, Volume 1

AcknowledgmentsThe development of this classification system represents a team effort. Whereas primary leadership,continuity, and maintenance have been provided by the science programs at The Nature Conservancy,the classification of vegetation types across the United States is based in large part on decades of fieldefforts by the ecologists across the network of state Heritage Programs. Numerous Conservancy andHeritage scientists have made important contributions to the development of the classification system.The list includes all of the Senior Ecology Group within the Conservancy and many past members ofthis Group. We would particularly like to acknowledge Dorothy Allard, Mark Bryer, Kim Chapman,Lisa Engelking, Bob Jenkins, Tom Rawinski, Rick Schneider, and Jack White. We would also like toacknowledge Kat Maybury for the editorial and coordination roles that she performed to bring thisvolume to completion.Work on this classification has been strongly supported by many federal programs at the nationaland regional level. The U.S. Forest Service and the U.S. Department of Interior Gap Analysis Programhave consistently provided a high level of involvement and support for the development of theclassification system and descriptions of types. The National Park Service’s Vegetation MappingProgram has furthered the development and documentation of the classification itself, along withstandards for its application to vegetation mapping. The use of this classification across these programsand partnerships has culminated in the refinement of this vegetation classification and informationsystem and its adoption as a standard by the Federal Geographic Data Committee (FGDC 1997).The subsequent development of the Ecological Society of America Vegetation Classification Panelhas been instrumental for the implementation of a broader documentation and review process.In summary, the development of this classification framework and the emerging list of vegetationtypes across the U.S. represents an extensive collaborative effort with a diverse set of partners. Thisclassification system is new to this country, and without such broad collaboration it would not havebeen possible.viiiInternational Classification of Ecological Communities: Terrestrial Vegetation of the United States

PrefaceThe committees of the Nature Conservancy have the task of assembling information on a country-wide basis andcoordinating the activities between states. Some of their immediate tasks are as follows: “A study and enumerationof the vegetation and biotic types of the United States and Canada.” A number of studies of this sort have beenmade for limited regions and for certain categories such as forest types and range types. No one has everundertaken to compile this information for the whole country. Estimated cost 5,000.Nature Conservation News. Annual Report of The Nature Conservancy, 1952.The mission of The Nature Conservancy, aninternational non-profit conservation organization, is to conserve species and natural communities through the protection of the lands and watersthat they need to survive. The Conservancy’sapproach to conservation relies on the consistentand systematic accumulation, management, andanalysis of scientific information on the “elementsof biological diversity”—specifically the status andlocation of plants, animals, and ecologicalcommunities. This information is collected andmanaged in partnership with an internationalnetwork of cooperating Natural HeritagePrograms and Conservation Data Centers. Theinformation is then used to help guide the Conservancy’s land acquisition and stewardship activitiesand to assist others in identifying priorities forbiodiversity conservation.From the beginning the Conservancyemphasized the need to protect ecologicalcommunities, or “biotic types,” as illustrated bythe quote from the 1952 Annual Report of TheNature Conservancy, above. Until recently theseecological communities were classified at thestate or regional level by the Conservancy andthe Natural Heritage Programs in North America,and these classifications helped direct conservation priorities on a state-by-state basis.Although these classifications have proved usefulfor many purposes (including conservationplanning, description of managed areas, andunderstanding of species habitats), they did notsupport the identification of regional and nationalecological units nor the associated setting ofregional conservation priorities. Many conservationists identified the need to move from anational conservation strategy focused primarilyon endangered species to a more comprehensiveapproach based on ecological communities (withmore specifically targeted actions on rare speciesprotection). A standardized national classificationof ecological communities would be the basis forimplementing such a strategy.To meet these objectives, the Conservancy,in conjunction with the Natural HeritagePrograms, undertook the development of ascientifically sound, consistent, and flexibleclassification system based on vegetation. A teamof Conservancy and Heritage ecologists has nowcompleted the first draft of a standardizednational vegetation classification system for theUnited States. Although this classification systemwas initially developed to support the conservation and management objectives of the Conservancy and the network of Natural HeritagePrograms, its utility has attracted a broader rangeof users in federal and state agencies, academicinstitutions, and other conservation organizations, as well as interest from internationalpartners. The identification of vegetation typesat the finest level of the classification hierarchy isfar from complete, and there are numerous stepsthat must be implemented to ensure the continued development and improvement of theclassification system. It is our objective to introduce the emerging system; provide informationPrefaceix

on its background, structure, and development;highlight some of the applications; and point outkey areas that still need to be developed. We havewritten this report to inform resource managers,scientists, and conservationists of what has beenaccomplished so far, to elicit feedback, and tosolicit an expanded set of partners.A classification of ecological communitiesor ecosystems using vegetation has bothadvantages and limitations. Vegetation is dynamic,and type definitions often require a high degreeof variability. However, vegetation is readilymeasured for both inventory and monitoringpurposes, it can be tracked efficiently at multiplescales, and it is a strong, if complex, indicator ofxthe ecological function of natural systems. Anational classification of vegetation can serve asan important component of a larger strategy tounderstand and conserve these natural systems.We are excited about its development and lookforward to its application both here in the U.S.and, in cooperation with other internationalgroups, in other countries.The work that is detailed in these twovolumes could not have been done without theConservancy’s willingness to support this effortover many years. We hope that this product willserve to further the work of understanding andconserving ecological systems in the UnitedStates and internationally.International Classification of Ecological Communities: Terrestrial Vegetation of the United States

IIIntroductionThe Need for a Standard Classificationof Ecological CommunitiesAttempts to understand the natural world havebeen directed at different biological andecological levels, from genes and species tocommunities and ecosystems. Efforts to conserve biological diversity can be focused at eachof these levels as well. Conservationists have oftenemphasized communities—assemblages ofspecies that co-occur in defined areas at certaintimes and that have the potential to interact withone another (Whittaker 1962, Reschke 1990,McPeek and Miller 1996). By describing,tracking, and preserving these ecologicalcommunities, they are able to protect a complexsuite of interactions not easily identified andprotected through other means.The Nature Conservancy (TNC) and theNatural Heritage Network1 have recognizedecological communities as important elementsof conservation for many years, and the bestoccurrences of these communities (as well as rareand imperiled species) have formed the basis forprotection decisions throughout the Conservancy’s history. The Conservancy recentlyreconfirmed the importance of using ecologicalcommunities as a key component in developingconservation strategies within an ecoregionalcontext (TNC 1996).Ecological communities constitute uniquesets of natural interactions among species, provide numerous important ecosystem functions(Costanza et al. 1997, Daily et al. 1997), andcreate part of the context for species evolution.In addition, by protecting ecological communities, many species not specifically targeted forconservation are protected as well. As such,communities become extremely importantconservation targets in areas where speciespatterns and ecological processes are poorlyunderstood. Communities also provide an important tool for systematically characterizing thecurrent condition of ecosystems and landscapes.Finally, change over time is often more efficientlymonitored in communities than in componentspecies. Changes may be detected by monitoringcomposition (changes in species abundance,proportions of endemics or exotics), structure(old growth characteristics, canopy features), andfunction (productivity, herbivory, patch dynamics,and nutrient cycling) (Noss 1990, Max et al. 1996).Until recently, however, there has been noaccepted standard for national or internationalcommunity classification. Community protection proceeded on a state-by-state or agency-byagency basis, based on independently developedclassifications. For the Conservancy and others,these classifications worked effectively for theconservation of important areas within states orjurisdictions, but from a national and international perspective, the lack of a standard systemresulted in unnecessarily redundant protectionof a few types and inadequate protection of manyothers.A common currency of ecological community types is clearly of fundamental importanceto the work of the Conservancy. Similarly, it is acritical tool for federal and state agencies that areresponsible for the conservation and management of biological diversity. In the absence of acommon classification, the results of manyinventory and monitoring programs, such asthose conducted in national forests and parks,state forests and parks, or fish and wildlife refuges,1The Natural Heritage Network is an informal designation of state and other programs that work cooperativelyto collect and manage information on rare species and natural communities.The Need for a Standard Classification of Ecological Communities1

cannot be integrated. As recently as 1995, Nosset al. concluded that a basic question—to whatextent the natural ecosystems in the United Stateshad been reduced in area or degraded in qualitydue to human activities—could only be answered“by a relatively crude approach because asystematic approach to understanding thesesystems at a national scale was not yet available.”The management implications of inconsistent classifications have also become moreapparent. Over the past few years, most federalresource management and land use agencies haveredefined their missions to address an “ecosystemapproach to management.” The meaning of ecosystem management and what this approach willaccomplish are articulated by each agency inrelation to its mission. Variation in the definitionof ecosystems among the agencies has led, insome cases, to considerably different interpretations of ecological units. A standard community classification system provides a consistentbasis for the characterization of the biologicalcomponents of different ecosystem units acrossthe physical and administrative landscape. Thus,a standard classification system contributes tothe formation of more precisely defined and lessvariable ecosystem units. It also allows for thecomparison of units that are defined andmanaged by different land management agencieswithin and among regions.A standardized classification system alsoprovides a valuable structure for framing andanswering important scientific inquiries aboutvegetation patterns and environmental processes.Such inquiries include (1) the comparison ofecological community richness and variability indifferent parts of the world, (2) the determination of the geographic distributions of specificvegetation types, (3) the elucidation of relationships between particular communities andenvironmental patterns or ecological processesacross the landscape, and (4) the developmentof mechanistic models that can explain thepatterns and dynamics of ecological communities, including responses to management andI22natural disturbance regimes.Thus, the relevance of a national vegetationclassification system is becoming clear to manyorganizations involved in conservation, naturalresource planning and management, and vegetation inventory, monitoring, and mapping. Insummary, the development of a standardnational community classification is regarded asa major step toward enhancing our ability tounderstand, protect, and manage the naturalresources of the United States (National ResearchCouncil 1993, Orians 1993, Noss et al. 1995,TNC 1996).Recognizing the need for a national andinternational classification of ecological communities, the Conservancy, in conjunction with theNatural Heritage Network, undertook thedevelopment of a scientifically sound, consistent,and flexible classification system. Early on, theConservancy identified the need for a separateclassification of each major ecological system(terrestrial, freshwater, marine, and subterranean), as each would require

New York Natural Heritage Program North Carolina Natural Heritage Program Ohio Natural Heritage Data Base Oklahoma Natural Heritage Inventory Ontario Natural Heritage Information Centre Oregon Natural Heritage Program Pennsylv