Succession and biomass allocation as controlled by Sphagnum in an Alaskan peatland

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Abstract
The vascular plant vegetation on active Sphagnum hummocks, on senescent hummocks, and in hollows of an Alaskan peatland was measured in several ways. Aboveground biomass and net primary production were greatest on senescent hummocks. Growth of hummock-forming Sphagnum mosses caused a significant increase in stem density and adventitious shoot production of Ledum palustre and Andromeda polifolia, while Vaccinium vitis-idaea showed a decrease in stem density; Rubus chamaemorus was unaffected. Overgrowth of vascular plants by Sphagnum resulted in significantly higher leaf/stem ratios in most of the shrub species. In addition, leaf turnover rates of the evergreen shrubs were modified. The growth of Sphagnum hummocks leads to a developmental stage in the vascular vegetation in which a large amount of structural biomass is present relative to leaf biomass. The rate of microsuccessional change in hummock–hollow complexes appears to be relatively high, at least in comparison to those macrosuccessional processes associated with permafrost formation and melting.