The Alaska Vegetation Classification - Alaska Geobotany Center ...

A lower well-developed shrub layer about 2 meters high is dominated by Oplopanaxhorridus, Rubus spectabilis, Ribes spp., and Vacciniurn spp. Common ferns andherbs include Gymnocarpium dryopferis, Athyriurn fifix-fernina, and Tiareffa frifofiafa.Distribution and site characteristics-Open Sitka spruce forest occurs most oftenat low elevations on active alluvial fans and flood plains. It is sometimes also presentat midelevations on steep mountain slopes adjacent to active channels and on activesnow avalanche paths. The soils are generally deep, well drained, and weaklydeveloped. The surface organic layer is thin because of frequent disturbance bywater flow, snow movement, or mass-wasting. The mineral horizons are mixed,thereby reflecting their alluvial or colluvial origin.Successional status-Open Sitka spruce (spruce/alder) communities appear to bestable over long periods of time. Periodic severe hydrologic disturbance seems tobe the main environmental factor allowing spruce and alder to share dominance onthese sites. Alder and Rubus specfabilis dominate these sites after clearcut logging.Conifers are slow to establish because of the thick shrub cover and the frequentdisturbance of soil by mass movement.Closely related types-These communities are similar to some closed tall alderscrub communities but have a substantial overstory of Sitka spruce. They also aresimilar to closed Sitka spruce communities but with less canopy cover.Photographs-Figure 11, this publication.Primary referencGMartin and others 1985.Communities-Picea sifchensis/A/nus sinuafa/Ca/amagrosfis canadensis (Viereck1979, Worley 1977). Picea sitchensis/Alnus spp. (Martin and others 1985).I.A.2.b. Open Western Hemlock-Sitka Spruce ForestDescription-These communities have an open overstory dominated by westernhemlock and Sitka spruce (fig. 12). Total tree cover is usually in the range of 45 to65 percent with most of it provided by hemlock, but Sitka spruce provides at least25 percent of the canopy cover. Mature western hemlock range from 21 to 27 meters(70 to 90 ft) tall and from 38 to 64 centimeters (15 to 25 in) d.b.h. Mountain hemlockmay occur but generally in small quantities. Mature spruce average 29 meters (95 ft)in height and 64 centimeters (25 in) in d.b.h. A well-developed shrub layer 1 to1.5 meters (3 to 5 ft) tall is dominated by Oplopanax horridus, Vaccinium spp.,Menziesia ferruginea, and Rubus specfabilis. Common herbs are Lysichifonarnericanurn, Rubus pedafus, and Afhyrium fikfemina.Figure 12-Open needleleaf forest ofwestern hemlock with scattered Sitkaspruoe, scattered Oplopanax horridusin the shrub laysr, and conspicuousLysichifon americanurn in the herb layeron Chichagof Island in southeastern Alaska.(Pholagraph munsry Jon Martin.)69