PARENT SESSION
Oral Session #75: Plant Communities: Vegetation Analysis. Presiding: J. Fralish.
Friday, August 10, 2001. 8:00 AM to 12:00 PM. Hall of Ideas F.
Experimental groundlayer restorations support description of Wisconsin oak savanna as "forb-lands," not "grass-lands.".
Leach, Mark1, Givnish, Thomas 1, 1
ABSTRACT- Oak savanna vegetation once dominated the southern-Wisconsin landscape, but today remnants with intact groundlayers are very rare. Their vegetation has long been described as "grasslands" and "prairies with trees." In our previously published study of 12 remnant savannas, we documented that forbs, not graminoids, dominated, except in sandier or sunnier microsites. That pattern, we reasoned, was consistent with ecological principals. However, among-site variation in management histories and local-species pools provided alternative explanations. To eliminate these factors, we initiated a planting experiment at the University of Wisconsin-Madison Arboretum. We sowed 411 1-m2 plots aligned in strips running from under to between oaks and arrayed across soils from sand to silt loam. Thus, the plots represented most of the soil x light microsites expected in Wisconsin's oak savannas. Each plot received equal numbers of seeds of 49 soil-generalist species. In addition, the 275 silt-to-loamy-sand plots received 35 soil specialist species and the 136 sandier plots received 34 specialists. Coverage data from the third growing season revealed distribution patterns in concordance with the savanna remnants. Forb cover increased with percent silt content and grass cover increased toward sunnier and sandier microsites. Bi-gradient distributions for C3 and C4 grasses and N-fixers were also similar to those found in remnants. These results provide strong independent support to the characterization of most Wisconsin oak savannas as forb-lands, not grasslands.
KEY WORDS: oak savanna, gradients, forbs, experimental restoration