Density of Large Snags and Logs in Northern Arizona Mixed-Conifer and Ponderosa Pine Forests

摘要

Large snags and logs provide important biological legacies and resources for native wildlife, yet data on populations of large snags and logs and factors influencing those populations are sparse. We monitored populations of large snags and logs in mixed-conifer and ponderosa pine (Pinus ponderosa) forests in northern Arizona from 1997 through 2012. We modeled density of large snags and logs as a function of forest type, time period, and environmental characteristics of sampled plots. Our objective was to build models that best explained current densities of these structures using these available covariates. The best model for density of large snags indicated that snag density was greater in mixed-conifer than in ponderosa pine forests, lower in plots with evidence of past timber or fuelwood harvest than in plots lacking such evidence, and covaried positively with mean slope and distance to road. The best model for density of large logs indicated that log density was greater in mixed-conifer than in ponderosa pine forests and covaried positively with solar insolation and surface ratio (an index of topographic roughness). The best snag model predicted that current US Department of Agriculture (USDA) Forest Service guidelines for retention of large snags were met only in mixed-conifer forests lacking evidence of past harvest activity. In contrast, the USDA Forest Service guidelines for retention of large logs were met in both forest types. Our results suggest that ease of human access and management history influence density of large snags, that current snag guidelines are unlikely to be met without considering these impacts, and that those guidelines may not be readily attainable in much of the landscape.