Available biomass:

Available biomass is the plant biomass that is available to the herbivore (deer or moose) at the time of the analysis.  In summer, it is the total standing crop of current year’s growth of a given species of plant.  In winter, the available biomass for a given species can be greatly reduced from its summer value by seasonal loss of above-ground tissue (deciduous species) and by burial by snow.  Black-tailed deer are not known to paw through snow in search of forage; thus food resources buried by snow are unavailable to deer.  Other food resources (e.g., lichens in trees, twigs of very tall shrubs) might be out of reach because they are too high for deer to reach.  However, after a snowpack has firmed up, especially with a frozen crust, black-tailed deer are able to walk freely on top of the snowpack.  Moose are known to “walk down” tall shrubs to reach high portions.  The “availability” of any forage is something that the user must consider when inputting the “available” plant biomass into the analysis.