Species composition of old-growth and riparian Sitka spruce–western hemlock forests in southeastern Alaska

We studied six 1.2-ha stands, two each of three types of forest: (1) old-growth, riparian floodplain forest, (2) old-growth, upland forest, and (3) 40-year-old, red alder (Alnusrubra Bong.) riparian forest originating after clear-cut logging of floodplain forest. Sitka spruce (Piceasitchensis (Bong.) Carrière) dominated the old-growth riparian stands and shared dominance with western hemlock (Tsugaheterophylla (Raf.) Sarg.) in the uplands. Regeneration was predominantly spruce in the alder riparian, spruce and hemlock in the old-growth riparian, and hemlock in the upland stands. Total understory biomass and ground cover did not differ significantly between forest types, but species-specific biomasses did differ (P < 0.05). Understory of the upland forest was dominated by early blueberry (Vacciniumovalifolium Sm.) and Alaska blueberry (Vacciniumalaskensis How.), while that of both riparian types was dominated by devilsclub (Oplopanaxhorridum (Sm.) Miq.). Other species-specific differences occurred in forbs (three species) and mosses (three species). Contrary to typical stand age–understory relations in upland conifer forests of the region, the understory of the 40-year-old red alder stands was very species rich and productive.