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 st udied in 16 even-aged stands of mixed Red Alder - Sitka Spruce - Western He mlock (Alnus rubra - Picea sitchensis - Tsuga heterophylla) forest. The sit es were upland sires, and the stands were 28-39 years old. We compared unde rstory within three categories of microsite types: Red Alder-dominated, con ifer-dominated, and mixed alder-conifer. Biomass of forbs and ferns differe d significantly (P < 0.05) between microsite types, being greatest in alder microsites, least in conifer microsites, and intermediate in mixed alder-c onifer microsites for all of the following: Circaea alpina, Galium trifloru m, Tiarella trifoliata, Viola glabella, Athyrium flix-femina, Gymnocarpium dryopteris, Thelypteris phegopteris, total forbs, total ferns, and total he rbs. Shrub biomass also was greatest in alder microsites but was least in m ixed microsites and intermediate in conifer microsites (P < 0.05 for Rubus spetabilis leaves and total shrub leaves). The greater shrub biomass in con ifer than mixed microsites resulted from several large parches of poor tree regeneration within 7 of the 16 stands; the other 9 stands had very low un derstory biomass in their conifer microsites, which is consistent with publ ished studies of understory dynamics in even-aged stands of the region. The results illustrate two important conclusions regarding current understandi ng of secondary succession following clearcutting in southeastern Alaska: ( 1) inclusion of Red Alder in the regenerating stand may result in much grea ter understory biomass than occurs in pure conifer stands; and (2) extrapol ation of data from small, uniform, fully-stocked research stands to the lan dscape level may underestimate understory biomass from poorly stocked parch es. Both conclusions have important implications for wildlife habitat in te rms 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 sec ondary succession is not necessarily the only successional pathway followin g clearcutting, in southeastern Alaska.