BALSAM FIR ON ISLE ROYALE - EFFECTS OF MOOSE HERBIVORY AND POPULATION-DENSITY

Abies balsamea population parameters were analyzed in Isle Royale National Park, Michigan, to assess Alces alces andersoni herbivory. In general, moose suppression of fir height growth and recruitment to the canopy increased with increasing moose density and decreasing fir density. Where fir densities were low, sapling heights were restricted to <1m regardless of moose density. In such sites, sapling growth suppression has been continuous since a peak in the moose population in the late 1920s. Canopy fir trees at most sites established prior to arrival of moose of Isle Royale around 1910. At high fir density release from growth inhibition was common following a period of low moose numbers from the mid-1970s to early 1980s. Here this release should facilitate recruitment of fir and effect replacement of canopy losses due to senescence. In other areas, however, continuing canopy losses and lack of recruitment due to intensive hervbivory by moose will greatly reduce the fir component of the canopy, effectively preventing any return to the fir-dominated forests of the past. -from Authors