Plant Communities of the Midwest - NatureServe

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y ABI and the Natural Heritage Network. Natural vegetation is defined as vegetation that occurs without regular human management, maintenance, or planting, and that generally has a strong component of native species. 3. It is based on existing vegetation. Vegetation classifications are typically based on either existing or potential natural vegetation (PNV). PNV types represent the projected mature or stable end points of vegetation development over time (late seral types). These types are projected to occur and persist on a site in the absence of disturbance, whether human-caused or natural (though some PNV concepts, such as those of Küchler [1964] recognize vegetation maintained by natural disturbances as PNV). PNV classifications offer insight into vegetation-site relationships and can be helpful in projecting the type of vegetation expected under a certain set of ecological factors. Nevertheless, disturbances have a strong influence on the structure and composition of vegetation, and each major successional stage following a natural disturbance (or a human-caused disturbance that closely mimics a natural one) may be biologically and ecologically distinct. Early successional communities also provide important habitat for many species. In addition to its usefulness for conservation purposes, a classification of existing vegetation makes fewer assumptions about natural processes or vegetation dynamics than PNV and allows the classification to be grounded in what is directly observable and measurable. Finally, the focus on existing vegetation can support a wide number of uses, including inventorying and monitoring the current status of ecological systems. For these reasons, the USNVC classification is based on existing vegetation, inclusive of all major stages of plant community dynamics. Although the USNVC framework is comprehensive with regard to existing vegetation— encompassing the spectrum from natural to cultivated—ABI has focused on the natural types, both naturally disturbed (early and mid-seral) and naturally undisturbed (late-seral). 4. It is a hierarchical system, defined by physiognomy and floristics. The USNVC has a hierarchical taxonomic structure with physiognomic criteria used at the coarsest levels of the hierarchy and floristic criteria used at the finest. Physiognomy refers to the structure (height and spacing) and overall shape of plants, and to leaf characteristics, such as seasonality, shape, size, and texture. These features provide a fast, efficient way to categorize vegetation on broad geographic scales. Physiognomic features can often be linked to remote sensing signatures, are easily recognized in the field, and can be applied even in places where very little information about the flora exists. Floristics refers to species composition. Using species composition or species groups to characterize vegetation reveals finer-scale local and regional patterns than are likely to be perceived using physiognomic characteristics. A combined physiognomic-floristic system allows for most of the advantages of both approaches and provides a unifying framework within which to relate typically coarse-scale physiognomic systems to more local and regional floristic systems. Structuring the USNVC in a hierarchical fashion allows it to be used at different taxonomic scales, depending on the amount of information available and the resolution needed. Hierarchy A key requirement of the classification system was that it would work not only in the United States, but also internationally. For this reason, the Conservancy and ABI chose to work with a physiognomic classification, the UNESCO world vegetation classification (UNESCO 1973). Several factors contributed to this decision. First, the UNESCO classification is the result of an international collaboration of scientists with considerable vegetation expertise, and has been used in many parts of the world. Second, it has a hierarchical arrangement, allowing it to be used at various conceptual and mapping scales, depending on the level of detail available or needed for a specific purpose. Third, its units are vegetation formations, i.e., vegetation types defined by physiognomy, with clear identification PLANT COMMUNITIES OF THE MIDWEST – 2001 8
criteria associated with each. This means that the system creates standard, easily identifiable units that may apply to many areas of the globe. Finally, the UNESCO formation levels contained associated ecological criteria (especially climate, topography, and hydrology) that helped clarify the geographic and ecologic scope of the units. The Conservancy and ABI made some amendments to the UNESCO classification in order to provide better representation of physiognomic conditions and more coherent links to floristic levels, which are not included in the UNESCO classification. An additional level was added between the “formation group” and the “formation” levels in order to allow a separation between cultural vegetation (e.g., corn fields, pine plantations) and natural vegetation. The USNVC system uses floristic units at the lowest levels—the association and alliance—that are similar in many respects to the Braun-Blanquet approach (Braun-Blanquet 1932, Mueller-Dombois and Ellenberg 1974). These floristic units are nested within the physiognomic units (Tables 1 and 2). Table 1. The framework of the International Classification of Ecological Communities (ICEC) and the U.S. National Vegetation Classification (Grossman et al. 1998). The top five levels are physiognomic, the bottom two levels are floristic. LEVEL PRIMARY BASIS FOR CLASSIFICATION EXAMPLE Class Growth form and structure of vegetation Forest Subclass Growth form characteristics (e.g., leaf phenology) Deciduous Forest Group Leaf type, corresponding to climate Cold-deciduous Forest Subgroup Formation Alliance Association Relative human impact (natural/semi-natural or cultural) Additional physiognomic and environmental factors, including hydrology Diagnostic/dominant species of uppermost or dominant stratum Natural/Semi-natural Lowland or Submontane Cold-Deciduous Forest Acer saccharum - Tilia americana - (Quercus rubra) Forest Alliance Additional diagnostic/dominant species in all strata Acer saccharum - Tilia americana / Ostrya virginiana - Carpinus caroliniana Forest Association Concept The association is the lowest level of the hierarchy, and the proposed basic unit for vegetation classification in North America north of Mexico (Grossman et al. 1998, Ponomarenko et al. 2000). It is defined as “a plant community type of definite floristic composition, uniform habitat conditions, and uniform physiognomy” (see Flahault and Schroter 1910). It is the combination of these interrelated criteria that conceptually defines the association (Figure 2). Typically, primary emphasis is given to floristics and physiognomy, with habitat features assessed through correlation with the vegetation. “Uniform” physiognomy and habitat may include patterned fine-scale heterogeneity (e.g., the canopy heterogeneity of grass-dominated and shrub-dominated patches in a shrub steppe or savanna). “Habitat” refers to the combination of environmental (site) conditions and ecological processes (such as disturbances or nutrient cycling) that influence the community. PLANT COMMUNITIES OF THE MIDWEST – 2001 9
Page 1: PLANT COMMUNITIES OF THE MIDWEST CL
Page 4 and 5: ISBN 0-9711053-0-8 © 2001 Associat
Page 6 and 7: This work has also benefited from i
Page 8 and 9: LISTS OF TABLES AND FIGURES List of
Page 10 and 11: Figure 1a. Distribution of alvar si
Page 12 and 13: (most associations were defined and
Page 14 and 15: particularly in Indiana and western
Page 18 and 19: Table 2. Illustration of the USNVC
Page 20 and 21: to year. In addition, the same asso
Page 22 and 23: journal articles, books, agency rep
Page 24 and 25: Once the cross-walk and review of t
Page 26 and 27: peatland, Great Lakes dune-swale co
Page 28 and 29: groupings, such as “forested peat
Page 30 and 31: Table 5. Definitions of ecological
Page 32 and 33: Level 1 distinguishes wetland ecolo
Page 34 and 35: PLATE 2 1. 1.4. Open and Emergent M
Page 36 and 37: PLATE 4 1. 2. 2.1. Shoreline Sand/M
Page 38 and 39: PLATE 6 2. 3. 1. 2.3. Rocky Uplands
Page 40 and 41: PLATE 8 1. 2. 2.5. Forests and Wood
Page 42 and 43: PLATE 10 1. 2. 2.9. Prairies/Grassl
Page 44 and 45: PLATE 12 Map of The Nature Conserva
Page 46 and 47: Great Plains Northern (Laurentian)
Page 48 and 49: Table 6. Ecological groups for the
Page 50 and 51: Grassland Forest and Woodland Prair
Page 52 and 53: High Tp w Woodland Only Mean Annual
Page 54 and 55: Box 1. Summary of information used
Page 56 and 57: Table 9. A list of plant communitie
Page 58 and 59: 1.4. OPEN AND EMERGENT MARSHES 1.4.
Page 60 and 61: 1.5.5.3. Great Plains Prairie Potho
Page 62 and 63: 1.6.4.5. Southeastern Coastal Plain
Page 64 and 65: 2.3.1.2. Northern Acid Rock Outcrop
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2.4.3.5. Eastern Alkaline Talus Lim
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2.5.2.3. Midwestern Mesic Hardwood
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2.5.6. Rocky Mountains Forests and
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2.8.3. Interior Highlands Oak Savan
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PLANT COMMUNITIES OF THE MIDWEST -
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Bliss, L. C. and G. W. Cox. 1964. P
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Jenkins, R. 1996. Natural Heritage
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Sneddon, L., M. Anderson, and K. Me
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