Seedbed and canopy cover effects on balsam fir seedling establishment in Isle Royale National Park

While balsam fir (Abies balsamea (L.) Mill.) dominated forests are vanishing from the southwest end of Isle Royale National Park, Michigan, renewal of fir stands is occurring on the northeast end. We speculate that the difference is related both to severe browsing by moose (Alces alces L.), and to the frequency of disturbances like fire and windthrow. A survey of 24 stands and in situ experimentation on Isle Royale show that balsam fir seedling survival is optimal under 40-79% canopy cover. Late-season and overwinter mortality in 1-year-old seedlings is highest under > 80% canopy cover, while germination is lowest under < 40% cover. We also rank germination substrates by ''preference ratios,'' and by comparing the overwinter survival of young fir seedlings on five natural media. We find best performance on hypnaceous moss, variable survival success on rotten wood, and highest mortality on broadleaf litter. However, ample seedling densities occur on the southwest end of the island, and the failure of fir to reach the overstory in this area is apparently not related to poor seedling establishment.