2iO 



Terrestrial Ecusyslem.s — Our Liviiiy Resaiirces 



For further information: 



Katheniie C. Kendall 



National Biological Service 



Glacier Field Station 



Glacier National Park 



West Glacier. MT 59936 



for western white pine (P. monticoUi). which 

 also suffers from rust. In some areas where 

 whitehark pine is regenerating, its competitors 

 should he eliminated. To perpetuate whitebark 

 pine at a landscape scale, fires must be allowed 

 to bum in whitebark pine ecosystems. 



Isolated populations may become e.xtinct 

 where mountain pine beetle or other agents kill 

 remaining resistant trees. To prevent loss ot 

 genetic diversity, seeds of these pines should be 

 collected throughout the species" range and 

 stored as insurance against catastrophic events. 

 To guide restoration efforts, more information is 

 needed on whitebark pine"s historical distribu- 

 tion, trends throughout its range, and rust epi- 

 demic dynamics. 



References 



,\nio. S.F.. and RJ, Hoff. 1989. Silvics of whitehark pine 

 iPiims albiccndis). U.S. Forest Senice Gen, Tech. Rep. 

 INT-2.S3. 1 1 pp. 



Keane, R.E.. and S.F. Amo. 199.3. Rapid decline of white- 

 hark pine in western Montana; evidence from 20-year 

 lemeasurenients. Western Journal of Applied Forestry 

 S(2);-t4-47. 



Kendall. K.C.. and S.F Amo. 199U. Whitebark pine— an 

 important hut endangered wildlife resource. Pages 264- 

 273 in U.S. Forest Service Gen. Tech. Rep. lNT-270. 



Olgilvie, R.T. 1990. Distnbution and ecology of whitebark 

 pine in western Canada. Pages .'i4-60 in U.S. Forest 

 Service Gen. Tech. Rep. INT-270. 



Oak Savannas 

 in Wisconsin 



by 

 Richard A. Henderson 



Eric J. Epstein 



Wisconsin Department of 



Natural Resources 



Oak savanna is a term given to a loosely 

 defined, yet well-recognized, class of 

 North American plant communities that were 

 part of a large transitional complex of commu- 

 nities between the vast treeless prairies of the 

 West and the deciduous forests of the East. This 

 system was driven by frec|uent fires and possi- 

 bly influenced by large herbivores such as bison 

 and elk. A wide range of community types was 

 found within this transitional complex: collec- 

 tively, they represented a continuum from 

 prairie to forest. The term "savanna" is general- 

 ly applied to a small group of related communi- 

 ty types in the middle portion of this continuum. 

 Savannas all have a partial canopy of open 

 grown trees and a varied ground layer of prairie 

 and forest herbs, grasses, and shrubs, as well as 

 plants restricted to the light shading and mix of 

 shade and sun so characteristic of savanna. 

 Oaks were clearly the dominant trees, and. 

 hence, the common use of the term oak savan- 

 na. Definitions of savanna tree cover range from 

 5% to 80% canopy; however, the lower canopy 

 covers of 5%-50% or 5%-30<7r are more widely 

 used criteria. Savanna types range from those 

 associated with dry. gravelly, or sandy soils: 

 those on rich, deep soils: and those on poorly 

 drained, moist soils. 



Oak savannas have probably been in North 

 America for some 20-25 million years (Barry 

 and Spicer 1987), expanding and contracting 

 with climatic changes and gaining and losing 

 species (on a geologic time scale) through evo- 

 lution and extinction. For the past several thou- 

 sand years, such savannas have existed as a rel- 

 atively stable band of varying width and conti- 

 nuity, from northern Minnesota to central Texas 

 (Figure). 



At the time of European settlement (ca. 

 1830), oak savanna covered many millions of 

 hectares. It varied somewhat in species compo- 

 sition from north to south and east to west, but 



Figure. Gross range of presettlement oak savanna in cen- 

 tral North America (adapted from Nuzzo 1986 and Smeins 

 and Diamond 1986). The shaded area represents the gen- 

 eral region in which oak savannas occurred, although this 

 region was not uniformly savanna. Significant blocks of 

 nonsavanna vegetation, such as prairie or forest, were also 

 present within it. Nor was oak savanna totally restricted to 

 this region. Small, disjunct outliers existed as far east as 

 Ohio and as far west as the Dakotas. 



Structure and functions were probably similar 

 throughout. In the upper Midwest (Minnesota, 

 Wisconsin, Michigan, Iowa. Illinois, Indiana, 

 and Missouri) there were an estimated 12 mil- 

 lion ha (29.6 million acres) of oak savanna 

 (Nuzzo 1986). Wisconsin's portion was 2.9 mil- 

 lion ha (7.3 million acres: Curtis 1959). As the 

 Midwest's rich soils were used for agriculture 

 and fire was suppressed, this ecosystem all but 

 disappeared from the landscape throughout its 

 range. Today, oak savanna is a globally endan- 

 gered ecosystem. 



Status 



In the early to mid- 19th century, the oak 

 savanna ecosystem was thoroughly fragmented 

 and nearly totally destroyed throughout its 

 range. Most of its acreage suffered from clear- 

 ing and plowing, overgrazing, or invasion by 

 dense shmb and tree growth caused by lack of 

 fire, lack of grazing, or btith. Consequently, oak 



