Microhabitat relations of the rare reed bent grass, Calamagrostis porteri subsp. insperata (Poaceae), with implications for its conservation

Calamugrostis porteri subsp. insperata was known from only two extant populations in Ohio prior to the late 1980s. Recent searching has documented more than 80 populations of this rare grass in five states. Although more populations exist than previously believed, the habitat requirements for this subspecies are still unknown. To quantify these requirements, data were collected on photosynthetic photo-flux density (PPFD), air and soil temperature, vapor-pressure deficits (VPD), soil moisture and depth, pH, percent organic matter. and associated species cover from three populations in southern Illinois. Leaf area, predicted total leaf area, and number of tillers per m(2) were measured to ascertain the relationship between vegetative performance and microenvironmental conditions. Detrended Canonical Correspondence Analysis (DCCA) was used to ordinate the samples using the cover of co-occurring species and the environmental variables. Leaf area, predicted total leaf area. and number of tillers were significantly related to the nine environmental variables at all three sites. The vegetative performance of this rare grass in southern Illinois seems to be determined by a complex suite of environmental factors, of which PPFD, VPD; and soil temperature are extremely influential, especially in the spring. The ordination shows that the three populations are distinctly separated, with total predicted leaf area, tiller density, soil moisture, soil temperature. air temperature. and pH being highly coil-elated to the ordination axes. Habitat modifications resulting in closed forest canopies detrimentally affect the vegetative performance of this taxon.