Northern red-backed vole northern forest and shrubland habitats. They occur in every major forest type in central Alaska. Plant species commonly found in areas occupied by northern red-backed voles include black spruce ("Picea mariana"), white spruce ("P. glauca"), quaking aspen ("Populus tremuloides"), paper birch ("Betula papyrifera"), alder ("Alnus" spp.), willow ("Salix" spp.), mountain cranberry ("Vaccinium vitis-idaea"), blueberry and bilberry ("Vaccinium" spp.), bunchberry ("Cornus canadensis"), and a variety of grasses and forbs. Important fungi, mosses and lichens include truffle ("Endogone fascilulata"), Schreber's moss ("Pleurozium schreberi"), mountain fern moss ("Hylocomium splendens"), sphagnum ("Sphagnum" spp.), and lichens ("Cladonia and Peltigera" spp.). The breeding season of northern
Carnivorous plant more or less than this optimum will take up less carbon dioxide than an optimal plant, and hence growing less well. These plants will be at a selective disadvantage. At zero investment the growth is zero, because a non-carnivorous plant cannot survive in a habitat with absolutely no soil-borne nutrients. Such habitats do not exist, so for example, "Sphagnum" absorbs the tiny amounts of nitrates and phosphates in rain very efficiently and also forms symbioses with diazotrophic cyanobacteria. In a habitat with abundant soil nutrients but little light (as shown above), the gross photosynthesis curve will be lower and flatter,