The Impacts of Ant Mounds on Sedge Meadow and Shrub Carr Vegetation in a Prairie Fen

Abstract

An important component of many fens is large mounds created by ants for nesting purposes. Because these mounds differ in microtopography, hydrology, and soil characteristics from the surrounding fen, they have the potential to strongly influence fen vegetation. This study examined the effects of ant mounds on plant cover and species composition in two vegetation types within a Michigan prairie fen complex. Vegetation was sampled on ant mounds and in control plots in sedge meadow and shrub carr vegetation types. Total plant cover was significantly greater on ant mounds than in control plots in the sedge meadow, but significantly lower on ant mounds than in control lots in the shrub carr. Plants varied in their response to ant mounds as a function of their wetland indicator status. Both facultative upland and facultative species occurred more frequently on mounds, whereas obligate wetland species were more common in control plots. There was no significant difference for facultative wetland species. Plant life form also strongly influenced patterns of distribution on mounds vs. control plots, with grasses occurring more frequently on mounds, and forbs and sedges occurring less frequently on mounds than in control areas. Thus, especially in the sedge meadow, ant mounds provide an important refuge for species more adapted to dry conditions.