Zonation of Sphagnum Mosses: Interactions among Shoot Growth, Growth Form, and Water Balance

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Abstract
Field measurements of tissue moisture content (% dry weight) and growth rates (min yr-1) of Sphagnum mosses were taken during two growing seasons in a subarctic bog near Fairbanks, Alaska. Shagnum angustifolium, a hollow-colonizing species, had lower tissue moisture contents and lower growth rates than Shagnum magellanicum and Sphagnum fuscum, hummock-forming species, under conditions, of low moisture availability. Conversely, under conditions of high moisture availability Sphagnum angustifolium maintained higher tissue moisture contents and higher growth rates than Sphagnum magellanicum and Sphagnum fuscum. All three Sphagnum species showed increased volumetric densities and stem spatial densities when growing farther from the water table. However, Sphagnum fuscum and Sphagnum magellanicum maintained higher volumetric densities than Sphagnum angustifolium in their respective microhabitats. Sphagnum zonation appears to be the result of a complex interaction between species-specific morphological and chemical characteristics, water balance, and terminal growth rates.