1994 Midwest Oak Savanna Conferences
Rich Henderson of the Wisconsin Department of Natural Resources provided a descriptive view of the categories of savanna and woodland, and in the process refined them. He distinguishes a simple two layered forest (which he called woodland) from multi-layered forest, and brush prairie from prairie.
ATTACHMENT 2: Midwest Savanna-Woodland Classification (The Nature Conservancy/Midwest Heritage Programs)
A PROPOSED CLASSIFICATION FOR SAVANNAS AND WOODLANDS IN
A classification is introduced for Midwest savannas as part of an effort sponsored by the U.S. Environmental Protection Agency and The Nature Conservancy to outline an ecosystem recovery plan for Midwest oak savannas and woodlands. The classification emphasizes how a number of different community types are currently being grouped under the phrase "Midwest oak savannas". Having done so, an attempt is made to construct meaningful distinctions based on physiognomy (outward structure or appearance of the vegetation). Physiognomy must be combined with other criteria to adequately define community types; hence physiognomic criteria will need to be somewhat flexible. A detailed classification combining physiognomic-(ecologic) and floristic criteria is presented that could help define the scope of restoration. A review of the classification's application in the Midwest is provided, including its application to state Heritage programs.
Appreciation is expressed to Pat Comer, Hannah Dunevitz, Eric Epstein, Mike Homoya, Max Hutchison, Tim Nigh, and John Pearson for their comments on this draft and the definition of savanna.
A Definition for Midwest Savannas
Based on discussions at the oak savanna conference, and the papers presented by R. Henderson and D. Nyberg as part of the conference, the proposal is made that we limit the use of the term savanna to tree canopies of (5) 10-25 (50)%. The term savanna will be used in the popular sense as a physiognomic category, but in the classification below will technically be called either "wooded grassland" or "shrub grassland."
Following Eiten (1986) and others, savanna (both wooded and shrub grassland) is defined as follows: "A savanna is any area where scattered trees and/or shrubs and other large persistent plants occur over a continuous and permanent groundlayer visually dominated by herbs, usually graminoids."
Woodlands, by contrast have an open to partially closed canopy where shrubs, forbs and other non-graminoid plants may dominate or codominate with the graminoids. The groundlayer is no longer the clear dominant. In this way the range of physiognomic classes for all vegetation can be defined as follows:
Additional categories can be recognized for SHRUBLAND (25-100%, including shrub thickets) and SHRUB GRASSLAND (10-25%). An outline of the limits of savanna are presented in Table 1.
This classification is offered for several reasons:
The application of these categories to specific sites does not require that a wooded grassland type fit the physiognomic definition exactly. Types, as reviewed below, are defined by their most characteristic physiognomy, but it will require knowledge of the site's characteristics and landscape processes to determine how best to manage the site. A certain amount of flexibility is also required because other criteria are used to define community types, such as dominant plant species or complete floristic data.
It should be stressed that the types proposed here are based on geographic patterns of major dominant species and their responses along ecological gradients. Thus they are intended to serve as initial guides for the diversity of savanna types in the Midwest. However, virtually all of these types have received little documentation. A concerted effort needs to be expended to characterize the distribution of these types throughout the Midwest.
Regional Relationships of Savanna Types
Classification of savanna is one step in the effort to identify where recovery activities should be focused. Another step is link the classification units into their ecological relationships on the landscape. An effort has been made to provide a very preliminary framework for undertaking such an analysis. The classification types presented here are grouped by broad categories geographically and structurally (Fig. A.).
Schematic representation of the relationship of savanna and woodland vegetation types in the Midwest. Relationships are portrayed geographically and are presented only as a means to further discussion on the relationships of vegetation to landscapes and ecological processes. See table 2 for a definition of the codes. SG=Shrub Grassland, WG=Wooded Grassland, W=Woodland
Table 1. The physiognomic levels that define the major types of Midwest savanna.
Table 2. The floristic levels that define the types of savanna and woodland within the major physiognomic groups. (see Table 1 for definitions of formations).
I.A.1 WOODED TALL GRASSLANDS WITH BROAD-LEAVED DECIDUOUS TREES (Tree savannas, Barrens)
POPULUS DELTOIDES WOODED GRASSLAND SERIES
WG.1. Populus deltoides/Panicum virgatum-Sorghastrum
nutans-Schizachyrium scoparium type
WG 2. Populus deltoides-(Salix nigra)/Spartina pectinata type
POPULUS TREMULOIDES WOODED GRASSLAND SERIES
WG 3. Populus tremuloides-Salix spp/Andropogon gerardii shrub
QUERCUS MACROCARPA-(Q. ALBA-Q.VELUTINA-Q.STELLATA) WOODED
WG 4. Quercus macrocarpa-(Q. alba-Q. velutina)/Andropogon gerardii
WG 5. Quercus macrocarpa/Andropogon gerardii type
WG 6. Quercus macrocarpa-Q. prinoides/Schizachyrium
scoparium-Sorghastrum nutans type
WG 7. Quercus macrocarpa-Q. stellata/Andropogon gerardii type
QUERCUS STELLATA-QUERCUS MARILANDICA WOODED GRASSLAND SERIES
WG 8. Quercus stellata-Q. marilandica/Andropogon gerardii type
QUERCUS ELLIPSOIDALIS-Q.VELUTINA WOODED GRASSLAND SERIES
WG 9. Quercus ellipsoidalis-Q. macrocarpa/Schizachyrium
scoparium-Koeleria cristata type
WG 10. Quercus velutina/Schizachyrium scoparium-Lupinus perennis
QUERCUS PALUSTRIS-QUERCUS MACROCARPA WOODED GRASSLAND SERIES
WG 11. Quercus palustris-Q. macrocarpa/Andropogon gerardii
I.A.2 WOODED TALL GRASSLANDS WITH BROAD-LEAVED DECIDUOUS and NEEDLE-LEAVED EVERGREEN TREES
PINUS SPP-QUERCUS SPP. WOODED GRASSLAND SERIES
WG 12. Pinus strobus-Quercus alba wooded grassland
WG 13. Pinus banksiana-Quercus velutina wooded grassland
II.A.1 SHRUBBY TALL GRASSLAND WITH BROAD-LEAVED DECIDUOUS SHRUBS (Shrub savannas, scrub barrens)
CORYLUS AMERICANA SHRUB GRASSLAND SERIES
SG 1. Corylus americana-Aronia melanocarpa/A.
gerardii-Schizachyrium scoparium type
POPULUS TREMULOIDES-QUERCUS SPP. SHRUB GRASSLAND SERIES
SG 2. Populus tremuloides-Quercus spp./Andropogon gerardii
shrub grassland type
III.A.1. TEMPERATE DECIDUOUS WOODLAND WITH EVERGREEN NEEDLE-LEAVED TREES
JUNIPERUS VIRGINIANA-QUERCUS MUEHLENBERGII-QUERCUS SPP. WOODLAND
W 1. J. virginiana-Quercus spp. (Q. rubra, Q. alba, Q. velutina)
W 2. J. virginiana-Quercus muehlenbergii woodland
W 3. J. virginiana-Q. muehlenbergii/Bumelia lanuginosa-Celtis
W 4. Juniperus ashei-Q. muehlenbergii woodland
PINUS BANKSIANA-QUERCUS VELUTINA-Q.ELLIPSOIDALIS WOODLAND SERIES
W 5. P. banksiana-Q. ellipsoidalis/Schizachyrium scoparium-Carex
PINUS ECHINATA-QUERCUS SPP. (Q. velutina-Q. stellata-Q. coccinea)
W 6. P. echinata-Q. velutina-Q. stellata-Q. coccinea/Schizachyrium
III.A.2. TEMPERATE DECIDUOUS WOODLAND WITHOUT EVERGREEN TREES
QUERCUS ALBA WOODLAND SERIES?
W 7. Quercus alba woodland
QUERCUS ALBA-Q. COCCINEA-Q. FALCATA-CARYA SPP. WOODLAND SERIES
W 8. Quercus alba-Q. falcata/Crotonopsis linearis woodland
W 9. Quercus alba-Q. falcata/Schizachyrium scoparium-Danthonia
QUERCUS MACROCARPA-MIXED OAK WOODLAND SERIES
W 10. Quercus macrocarpa-Q. alba woodland
W 11. Quercus macrocarpa bluff woodland
QUERCUS MACROCARPA-QUERCUS MUEHLENBERGII WOODLAND SERIES
W 12. Quercus macrocarpa-Q. muehlenbergii/Andropogon gerardii
mesic ravine woodland
W 13. Quercus macrocarpa-Q. muehlenbergii/rock outcrop
QUERCUS STELLATA-QUERCUS MARILANDICA WOODLAND SERIES
W 14. Quercus stellata-Quercus marilandica/Andropogon gerardii
W 15. Q. stellata-Q. marilandica-Carya texana/Danthonia spicata-S.
W 16. Quercus stellata-Q. alba-Q. velutina/Schizachyrium scoparium
W 17. Quercus stellata/Danthonia spicata-Crotonopsis elliptica
W 18. Quercus marilandica/Danthonia spicata-Antennaria
W 19. Quercus stellata-Quercus marilandica (Q. falcata)/Schizachyrium
III.B.3 TEMPERATE ALLUVIAL WOODLAND WITHOUT EVERGREEN TREES
QUERCUS MACROCARPA ALLUVIAL WOODLAND SERIES
W 20. Quercus macrocarpa-Mixed Hardwoods/ woodland
QUERCUS PALUSTRIS-QUERCUS BICOLOR WOODLAND SERIES
W 21. Quercus palustris-Q. bicolor/ woodland
W 22. Quercus palustris-Q. bicolor/Spartina pectinata-Carex spp.
Table 3. A crosswalk of the major tree and shrub savanna types with state Heritage program classifications. Woodland classification is not fully crosswalked yet.
This list reflects an attempt to identify plants consistently associated with oak barrens on sand in the central Midwest. It is by no means complete. It includes plants from those portions of the barrens ecosystem that are exceptionally dry, as well as those inclusions that are seasonally wet, e.g., sandy swales. Those marked with an asterisk are more or less restricted to sandy oak barrens, at least in the region. Several of the others also occur in other environments, but many reach their greatest expression in the barrens. This list is compiled from species lists of Indiana nature preserves, and information from Vegetation of Wisconsin (Curtis 1959), and Plants of the Chicago Region (Swink and Wilhelm 1979).
Compiled by Michael Homoya, Indiana Department of Natural Resources, 1993.
+ = These species have ranges in common with the eastern and southeastern flora (taken from Radford et al. 1968). They occur in a variety of habitats, but most are in dry, sandy or rocky habitats (barrens or barren-like environments).