Red Alder, Alnus rubra, as a Potential Mitigating Factor for Wildlife Habitat Following Clearcut Logging in Southeastern Alaska

Within-stand variation in understory species composition and biomass was studied in 16 even-aged stands of mixed Red Alder Sitka Spruce Western Hemlock (Alnus rubra Picea sitchensis Tsuga heterophylla) forest. The sites were upland sites, and the stands were 28-39 years old. We compared understory within three categories of microsite types: Red Alder-dominated, conifer-dominated, and mixed alder-conifer. Biomass of forbs and ferns differed significantly (P < 0.05) between microsite types, being greatest in alder microsites, least in conifer microsites, and intermediate in mixed alderconifer microsites for all of the following: Circaea alpina, Galium triflorum, Tiarella trifoliata, Viola glabella, Athyrium filix-femina, Gymnocarpium dryopteris, Thelypteris phegopteris, total forbs, total ferns, and total herbs. Shrub biomass also was greatest in alder microsites but was least in mixed microsites and intermediate in conifer microsites (P < 0.05 for Rubus spectabilis leaves and total shrub leaves). The greater shrub biomass in conifer than mixed microsites resulted from several large patches of poor tree regeneration within 7 of the 16 stands; the other 9 stands had very low understory biomass in their conifer microsites, which is consistent with published studies of understory dynamics in even-aged stands of the region. The results illustrate two important conclusions regarding current understanding of secondary succession following clearcutting in southeastern Alaska: (1) inclusion of Red Alder in the regenerating stand may result in much greater understory biomass than occurs in pure conifer stands; and (2) extrapolation of data from small, uniform, fully-stocked research stands to the landscape level may underestimate understory biomass from poorly stocked patches. Both conclusions have important implications for wildlife habitat in terms of understory vegetation for food and cover. The potential of Red Alder as a mitigating factor for wildlife habitat following clearcutting in the region needs additional study of disturbance-site-understory interactions. Our results, however, indicate that an understory-exclusionary stage of secondary succession is not necessarily the only successional pathway following clearcutting in southeastern Alaska.