The vegetation and its environments in Maine peatlands

This study is based on releves from 96 peatlands representing the typologic, environmental, and geographic variation of Maine peatlands, and on peat pore-water chemistry at a representative set of 51 of these peatlands. We give optima and tolerances of pH, Ca, P, NO3-N, NH4-N, and influence of upper on lower vegetational strata for the 73 most common vascular plant species, excluding sedges, which are presented elsewhere. The program TWINSPAN differentiated 30 plant communities. Environments of the first seven TWINSPAN divisions differed largely by Ca, pH, P, NH4, Fe, microrelief, substrate depth, degree of humification, and climate. A canonical correspondence analysis (CCA) with forward selection entered pH, P, Na, Fe, Ca, Mg, and percent H2O as the minimum number of variables which best explains species variation. A CCA of the lower strata vascular plants demonstrated the importance of the upper strata (percent overstory) on species' distributions. Gradients of pH-alkalinity and percent overstory are primary in determining Maine's peatland vegetation. Other important gradients are percent H2O in upper peat, concentrations of lithic elements (P, Fe, Mn, Al, and Si) in pore water, and climate. Although these gradients partially covary, some of the variation in species' distributions can be attributed to independent aspects of individual gradients. Species richness across the range of peatland types is related to pH-alkalinity for vascular plants, and to percent H2O, microrelief, and percent overstory for bryophytes.