Estimating snag and large tree densities and distributions on a landscape for wildlife management
- Lisa J. Bate, Edward O. Garton, Michael J. Wisdom
- Gen. Tech. Rep. PNW-GTR-425. Portland, OR…
We developed efficient and accurate methods for sampling snags and large trees important to wildlife. These methods are described in detail in a recent Forest Service publication, which also includes spreadsheets, macros, and instructions to conduct surveys and analyses to estimate densities and distributions of snags and large trees on a landscape. These methods focus on optimizing sampling effort by choosing a plot size appropriate for specific forest conditions encountered. Two methods for assessing density are available. Method I requires sampling until a desired precision is obtained for a density estimate. Method II is designed to test for differences in observed snag density versus a desired target density. After collecting a minimum of 60 samples under method II, one may test for a significant difference between the observed and targeted densities. In addition, data can be used to calculate a distribution index. The value obtained from the distribution index helps managers assess whether the current distribution of snags and large trees across a subwatershed is adequate to meet the habitat needs of territorial cavity-nesters and other wildlife species. Wildlife use of snags and large trees may also be evaluated.