Effects of Stand Age on Species Composition and Browse Density in Northeastern Minnesota

Abstract

Large ruminant herbivores like moose spend most of their time foraging and ruminating to acquire and process enough plant biomass to meet energy and nutrient requirements. In northeastern Minnesota, moose forage in a mosaic of forest stands with ages shaped by harvest and other disturbances. Distribution and abundance of browse species varies across the landscape and each browse species has unique growth patterns and a patchy distribution within and among different stand types. We measured browse availability and use along foraging paths of GPS radio-collared moose and within randomly selected regenerating stands in northeastern Minnesota. We measured all sites using traditional methods and a method that simulates moose foraging behavior by measuring large feeding stations. At each site we measured available species composition and available browse density. We tested three hypotheses: (1) the proportion of available browse species common in the diet along foraging paths would be greater than within randomly selected regenerating stands, (2) the density of available browse species would be greater along foraging paths than within randomly selected regenerating stands, and (3) the density of available twigs would be highest in young stands and decrease with stand age. Paper birch, willow, and quaking aspen were common in young stands while hazel, mountain maple, and balsam fir (winter) or juneberry (summer) were common in older stands. Browse density also changed with stand age, but the changes in species composition and browse density were similar along foraging paths and within randomly selected regenerating stands indicating that moose habitat restoration projects can effectively create forage for moose. In areas with and without collared moose the simulated browsing method was an effective tool for measuring browse availability and use.