Estimating the impacts of harvest distribution on road-building and snag abundance

Various patterns of harvest in forests influence the length of road and number of stream crossings required. Snags are removed directly by harvesting, but they are also removed along road and opening edges to ensure worker safety. To assess the potential impacts of rate of harvest and pattern of harvest in an oldforest-dominated montane landscape, we developed a spatially explicit landscape dynamics model, which includes submodels for snag removal, harvesting activities, and access management. The model assesses the amount of new road construction and number of streams crossed by new roads, as well as changes in snag density and configuration across the landscape over a time horizon of several decades, in response to various harvesting patterns. We estimated that a dispersed 40-ha cutblock harvest pattern required about one-third more kilometres of new road over a 50-year period and removal of up to 70% more snags per hectare of harvest for safety purposes, compared with a harvest pattern based on natural-patch size distribution. Each 20% increase in stand-level retention resulted in a roughly equivalent increase in new road required. Up to eight times as many snags were removed per hectare of harvest for safety purposes at a stand-level retention of 70% than at a stand-level retention of 10%. The model appears to be an effective tool for determining the future impact of various harvest-pattern options on a number of important indicators of ecological impact.