United States Department of Agriculture A Vegetation Forest Service Pacific Southwest Forest and Range Classification System Experiment Station General Technical Report PSW-63 for Use in California: Its Conceptual Basis Timothy E. Paysen Jeanine A. Derby C. Eugene Conrad The Authors: TIMOTHY E. PAYSEN, a research forester, is assigned to the Station's chaparral and related ecosystems research unit, with headquarters at Riverside, Calif. He earned a bachelor of science degree in forest management at Humboldt State College (1969) and a doctorate in applied statistics at the University of California, Riverside (1978). JEANINE A. DERBY is a forest botanist, San Bernardino National Forest, San Bernardino, Calif. She received a bachelor's degree in biology (1974) at the University of California, Riverside, and a master's degree in biology (1979) at California State University, San Bernardino. C. EUGENE CONRAD heads the Station's research unit studying the management of chaparral and related ecosystems, with headquarters at Riverside, Calif. He earned a bachelor's degree in agriculture (1956) and a master's degree in range management and plant ecology (1959) from Oregon State University. He joined the Forest Service and Station's research staff in 1961. Acknowledgments: We thank Ivan E. Parker of the Pacific Southwest Region's Land Management Planning Staff, Forest Service, U.S. Department of Agriculture, for his active participation in developing earlier manuscript drafts and for his pungent critique of concepts and philosophies that would have earned for him the right to coauthorship had time and priorities allowed him to become involved in developing the final draft. Responsibility for final content, concepts, and philosophies rests with us. We also thank members of the California Interagency Vegetation Task Group who provided technical review of this paper: Norden H. Cheatham, University of California Systemwide Administration; Harlan C. DeGarmo, Soil Conservation Service, U.S. Department of Agriculture; Don A. Duncan, Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; E. Lee Fitzhugh, University of California Cooperative Extension; Glen Hols- ein, The Nature Conservancy; Nancy Tosta Miller, California Department of Forestry; Dale A. Thornburgh, Humboldt State University; and John W. Willoughby, Bureau of Land Management, U.S. Department of the Interior. Publisher: Pacific Southwest Forest and Range Experiment Station P.O. Box 245, Berkeley, California 94701 December 1982 A Vegetation Classification System for Use in California: Its Conceptual Basis Timothy E. Paysen Jeanine A. Derby C. Eugene Conrad CONTENTS Introduction ..................................................................................................... 1 Vegetation Classification in California ............................................................ 2 Classification System for California ................................................................ 2 Association: The Basic Unit ......................................................................... 3 Series: Overstory Species ............................................................................. 3 Subformation: Morphological Similarities ................................................... 4 Formation: Physiognomic Similarities ......................................................... 4 Phase: Variability in Communities .............................................................. 4 Nomenclature ............................................................................................... 5 Conceptual Basis of the System ....................................................................... 6 Performance Requirements .......................................................................... 6 Design Criteria .............................................................................................. 7 Concepts Useful in Field Application .............................................................. 9 Plant Community Organization .................................................................... 9 Succession and Development ..................................................................... 10 Potential Vegetation and Climax ................................................................ 10 Apparent Instability in Stable Communities .............................................. 10 Appendix: Classification System Correlations ............................................... 11 References ...................................................................................................... 13 long-standing communication problem for people who classification devised by Kuchler (1964) as a basis for map- Amanage resources is now entering a critical stage. In the ping potential natural vegetation of the United States can be past, different vegetation classification "languages" became included. Kuchler's potential natural vegetation is defined as current, in line with the emphasis on specific resource man- that which would exist if man were removed and subsequent agement responsibilities or functions, such as timber or plant succession telescoped into a single moment in time. wildlife. With the change in emphasis toward interdisciplinary Many classification systems go beyond the mere description management, the diversity of these languages hampers effect- of vegetation. Some systems focus on the ecology of vegeta- tive planning and coordination. Because each functional or tion; these systems relate particular kinds of vegetation to the technical vegetation classification system reflects a different characteristics of the environments that they grow in. Thus, we viewpoint, no one system can be used by all disciplines or find plant communities and vegetation types with such names agencies. as Alkali Sink Scrub, Alpine Cushion Plant, Palm Oasis The system described in this report solves the communica- Woodland, Foothill Oak, or Desert Transition Chaparral. tion problem. It addresses only the vegetation component of Other systems focus specifically on ecosystems that are ecosystems; it is a plant community taxonomy based on the characterized by vegetation; these systems classify land units fundamental concepts of classification. It can thus serve as a or ecosystems, but use names derived from vegetation classifi- crosswalking mechanism, or general language, with common cation schemes (see Daubenmire 1968, Hall 1976, Layser and acceptance in resource management. Properly used, it is a Schubert 1979, Pfister and Arno 1980). A different use of consistent framework on which to build better languages vegetation nomenclature is found in systems for classifying adapted to specific resource functions. land or ecological units that represent more general biological The system addresses a basic plant community unit at five systems (Brown and others 1979, Dansereau 1951, Walter levels of descriptive detail, four of which are members of a 1973). Included in this last group, and geared towards map- formal hierarchy. Floristic criteria are used for the basic unit at ping vegetation on a global scale, are Fosberg's system (Fos- the most precise level, the plant Association, and for the more berg 1967) and the UNESCO system (UNESCO 1973). The generally descriptive unit, the Series. Physiognomic and mor- distinction between the kinds of systems described in this phological criteria are used to aggregate these basic units to the paragraph and those that classify vegetation alone is often Subformation and Formation levels of the system. The fifth missed by practitioners, and occasionally by the system devel- level, the Phase, which is outside of the hierarchy, provides a opers themselves. flexible tool for description of vegetation characteristics re- Vegetation classification systems have been a necessary lated to resource function or other specific by-product of inventory, mapping, land classification, or objectives. ecosystem classification systems. In timber and range man- The development of the present system has taken place agement, for example, vegetation growing sites are placed in against a background of many attempts to classify vegetation. categories defined by management criteria (Eyre 1980; U.S. In the aggregate, existing systems reflect a variety of purposes Dep. Agric., Forest Serv. 1979; U.S. Dep. Agric., Forest and an assortment of descriptive scales, but each system meets Serv. 1975). Some systems serve as a point of departure for a specific objective. Systems have been designed to organize understanding the structure and dynamics of vegetation vegetation according to functional resource management (Braun-Blanquet 1932). Poulton (1972) developed a plant criteria, to describe vegetation associated with land units or community classification system in order to complete a land ecological units, to distinguish structural types or floristic cover map legend. assemblages, or to stratify vegetation into recognizable areal This report describes a Vegetation Classification System units. Systems came into being to ease management activity and its conceptual basis. It provides users of the System with (inventory, land allocation, planning), to illustrate ecological information that will facilitate its consistent application in the relationships, or to provide a framework for understanding field, clarifies the System's relevance to various classification vegetation dynamics. Systems can be designed to address a problems, and suggests methods for its