MULTIPLE LIMITING GRADIENTS IN PEATLANDS - A CALL FOR A NEW PARADIGM

Peatlands often have readily apparent gradients of plant species distr ibutions, biogeochemistry, and hydrology across several spatial scales . Many inferences have been drawn about the colinearity of these gradi ents, and these assumptions have become ingrained in the terminology t hat describes and classifies peatlands. We review the Literature and p resent some of our own data that show that many of these inferences ar e either wrong or correct only under a limited set of ecological condi tions. We examine historical classification schemes of peatlands and, in this context, gradients of alkalinity, pH, nutrient availability fo r plant growth, nutrient mineralization, hydrology, and decomposition. We further suggest a strictly defined set of terms to describe separa te gradients of hydrology, alkalinity, and nutrients that limit plant growth in peatlands. Specifically, we make the following suggestions c oncerning terminology. (1) The suffix ''-trophic'' should only be used when referring to nutrients that directly Limit plant growth at natur al availabilities (e.g., eutrophic and oligotrophic). (2) Terms such a s circumneutral, moderately acid, and very acidic (or alternatively st rong, intermediate, and weak) should be used to describe the pH of pea tlands. (3) Ombrogenous and geogenous (or limnogenous, topogenous, and soligenous) should be used to describe the hydrology of peatlands. (4 ) The terms bog and fen should be defined broadly based on water/soil chemistry and dominant plant species without accompanying assumptions regarding hydrology, topography, ontogeny, nutrient availability, or t he presence or absence of nondominant indicator plant species. Better yet, the generic term peatland be used when possible to avoid confusio n about conditions that may or may not be present at a particular site .