Growth and production dynamics of boreal mosses over climatic, chemical and topographic gradients

Three basic questions arc addressed in this paper. Each of them considers a separate aspect of moss growth and production. A common theme throughout is that moss populations are dynamic, highly active entities. The study of these dynamics can tell us not only about the mosses themselves but also about the systems in which they live. The following conclusions are reached. (1) Moss populations are organized into complex canopies, some having at least 6000 leaves cm“‘. Drought-tolerant mosses may achieve high rates of growth when moist, but generally are dry and inactive a large percentage of lime. (2) For the ectohydric, drought-tolerant moss, Hylocomium splendens, growth is highly variable over its North American boreal range and can be related to precipitation and continentality. However, for the endohydric, less drought-tolerant moss, Polytrichum strictum, growth is more constant over its North American range and is not as distinctly related to broad macroclimatic patterns. It may have nutrient limited growth, whereas Hylocomium splendens may have climatically limited growth. (3) (a) In mires, calcium, magnesium, sodium and hydrogen ions are important chemical factors that are closely correlated to mire type. Available amounts of nitrate, ammonium, phosphorus and total organic nitrogen in surface waters do not correlate with mire type; likewise, they do not increase across the bog-rich fen gradient. Extreme-rich fens and bogs have about the same concentrations of these components, but water-flow differences may modify the total nutrient input during a season in fens, (b) Moss production in extreme-rich fens is similar to, or somewhat less than, in bogs and poor fens. However, decomposition is much greater in extreme-rich fens. Peat accumulation may, therefore, be greater in bogs and poor fens than in extreme-rich fens, (c) Net production on bog hummocks is about half that of hollows, whereas in poor fens and rich fens, production on hummocks is greater than or equal to that in the hollows. Decomposition in poor fens and bogs is much less on hummocks, while there are few differences between height extremes in rich fens. Hummocks appear to be maintained in bogs due to low decomposition rates, while in rich fens they are maintained by relatively high production, (d) Production rates of Sphagnum species are generally similar to or higher than those of brown mosses. Different species of Sphagnum dominate different parts of the chemical and topographic gradients in bogs while different brown moss species dominate parts of comparable gradients in rich fens.