Moose browsing on Scots pine: impacts on growth, timber production, management and economics

Modern forestry practice with clearcuts and subsequent regeneration of trees provides ample food for deer and is a key driver for maintaining a dense and highly reproductive moose population in the Nordic countries. However, moose browsing causes heavy damage to growth and wood quality of Scots pine (Pinus sylvestris), economically one of the most important tree species in this region. The consequences of moose browsing on pine for timber production and economics remain poorly quantified. We address this by studying potential impacts of browsing damage on growth, management, timber production and economic returns in a simulation-optimization framework. Browsing damage functions based on forty-year field observations were implemented in an individual-tree growth and yield simulator to project stand development under alternative forest management alternatives. By including economic parameters, we assessed how management would be shifted over the next 200 years to mitigate impacts of browsing over a range of productivity classes, regeneration densities, browsing levels and discount rates. The most pronounced management adaptation was prolonging rotation age up to twenty years. Still, browsing caused timber production to be reduced by up to 1.5 m3 ha-1 yr-1 and up to 25 percent. Land expectation values were likewise heavily impacted, for a discount rate of 2% p.a., browsing turned forest management on medium-productive land unprofitable. The results may guide policymakers and forestry and wildlife practitioners in balancing moose population with timber production and economic objectives.