Summary
Loss of top predators may induce a “trophic cascade” within forested ecosystems by releasing browsing ungulate populations that may in turn impact future forest dynamics. Forest Service scientists and their research partners applied a landscape disturbance and succession model (LANDIS-II) to investigate how the moose population could interact with the forest ecosystem of Isle Royale National Park in Michigan over the next century under three different wolf predation scenarios: no predation, weak (long-term average predation rates), and strong (higher than average rates). Increasing predation rates led to lower peak moose population densities, lower biomass removal rates, and higher estimates of forage availability and landscape carrying capacity, especially during the first 40 years in the simulations. Thereafter, moose population density was similar for all predation scenarios, but available forage, moose carrying capacity, and forest composition continued to diverge among predation scenarios. High browsing rates led to reductions in aspen, birch, and balsam fir, and increases in white and black spruce, especially after the simulation year 2050, when existing aspen-birch stands at Isle Royale are projected to naturally decline. The research results support the concept of a trophic cascade in this system, and can help inform alternative predator management strategies as they may affect ungulate populations and forest succession.
