An ordination study of mangrove swamp communities in West Africa

The most important environmental gradients of Maine peatlands are geologic substrate and alkalinity. Other gradients are coastal-inland climate, moisture content of the peat, P and K concentrations, and shade. Abundance weighted means of pH, Ca, and moisture content of peat are given for the 48 most frequently occurring bryophyte and lichen species. A TWINSPAN differentiated twenty associations. Environments of the first four TWINSPAN dichotomies differed largely by pH and related variables, though Fe, %H₂O, shade, microtopography, and degree of humification were also significant. A CCA with forward selection entered pH, P, Fe, Na, %H₂O, shade, and a climate factor as the minimum number of variables which best account for the species variation. Bryophyte and lichen distributions are determined primarily by edaphic and hydrologic factors, which determine the kinds and amounts of mineral solutes in peat interstitial water. Two independent chemical gradients were identified: (1) the acidity-alkalinity gradient related to base cation concentrations, and (2) a gradient of Fe, Al, Mn, and Si related to shallowness of peat and inputs from granitic lithologies.