THE VEGETATION AND ITS ENVIRONMENTS IN MAINE PEATLANDS

This study is based on releves from 96 peatlands representing the typo logic, environmental, and geographic variation of Maine peatlands, and on peat pore-water chemistry at a representative set of 51 of these p eatlands. We give optima and tolerances of pH, Ca, P, NO3-N, NH4-N, an d influence of upper on lower vegetational strata for the 73 most comm on vascular plant species, excluding sedges, which are presented elsew here. The program TWINSPAN differentiated 30 plant communities. Enviro nments of the first seven TWINSPAN divisions differed largely by Ca, p H, P, NH4, Fe, microrelief, substrate depth, degree of humification, a nd climate. A canonical correspondence analysis (CCA) with forward sel ection entered pH, P, Na, Fe, Ca, Mg, and percent H2O as the minimum n umber 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 p eatland vegetation. Other important gradients are percent H2O in upper peat, concentrations of lithic elements (P, Fe, Mn, Al, and Si) in po re water, and climate. Although these gradients partially covary, some of the variation in species' distributions can be attributed to indep endent aspects of individual gradients. Species richness across the ra nge of peatland types is related to pH-alkalinity for vascular plants, and to percent H2O, microrelief, and percent overstory for bryophytes .