The Alaska Vegetation Classification - Alaska Geobotany Center ...

I.C. Mixed ForestFigure 33-Closed mixed forest of paper birch andwhite spruce wih a sparse shrub layer of Viburnumsdule and Rosa aucularis.In mixed forest, neither needleleaf nor broadleaf tree species have clear dominance.Both needleleaf and broadleaf contribute 25 to 75 percent of the total canopy cover.Tree cover totals at least 10 percent.I.C.1. Closed Mlxed ForestClosed mixed forest communities have tree canopy coverages ranging from 60 to100 percent. Dominance in the tree layer is shared between broadleaf and needleleafspecies, with both groups contributing from 25 to 75 percent of the total tree cover.I.C. 1.a. Closed Sprucepaper Blrch ForestDescrlptlon-These stands are made up of paper birch and either white or blackspruce or a mixture of both (fig. 33). White spruce-paper birch stands generally aredominated by large white spruce and paper birch that reach maximum diametersof about 30 to 35 Centimeters (12 to 14 in) d.b.h. and maximum heights of 18 to23 meters (60 to 75 ft). Tree regeneration is usually scattered and largely restrictedto spruce. Stands commonly reach 140 years of age. Older stands tend to be moreopen (total tree cover decreases), and the relative cover of sptuce increases as theovermature birch trees drop out. The birch component of these stands is even aged:the spruce component becomes more uneven aged as the stand matures. A moderatelydense tall shrub layer consisting of Alnus crispa, Salix bebbiana, andS. scouleriana often is present. A low shrub layer dominated by Rosa acicularis orViburnum edule, or both, is characteristic of these communities. Other common lowshrubs include Ribes frisfe, Spiraea beauverdiana, and Vaccinium vifis-idaea. Commonherbs include Calamagrosfis canadensis, Cornus canadensis, Linnaea borealis,Merfensia paniculafa, and Equisetum arvense. A patchy carpet of feathemossescommonly dominated by Hylocomium splendens occupies the forest floor.Black spruce-paper birch stands 40 to 70 years old have black spruce averaging7 to 9 centimeters (3 to 4 in) d.b.h. and 2 to 17 meters (6 to 56 ft) tall. Black spruceseedlings and saplings are common. Paper birch, ranging up to 20 centimeters (8 in)d.b.h.. are less abundant than black spruce. Little birch regeneration is present. Thebirch become overmature and slowly die as the stand ages: few are left by the time