Historical stand reconstruction in ponderosa pine forests to guide silvicultural prescriptions

Abstract

We reconstructed the historical stand structure and spatial patterning of fire-maintained ponderosa pine forests in the Eastern Cascades of Washington to develop and design silvicultural prescriptions to restore historical structure and composition. The structure of the dominant overstory was inferred from the size and spatial patterning of stumps, logs, snags, and live trees (>140 years of age) within 48 0.5 ha plots. Size class distributions, basal area, and spatial distribution of historical trees were compared among plant association groups representing a range of environmental conditions. Using spatial point pattern analysis, we found that significant clumping at fine scales (0–15 m) existed historically. Spatial patterning of present day and historical trees of four comparable plots suggests that while strong clumping exists in present day stands, the largest trees today exhibit less clumping than did large historical trees. Historical SDI (260) for dominant overstories was nearly the same as threshold for serious beetle mortality (263) for ponderosa pine. Cut-tree marking was carried out within 15 m radius circles, as guided by the spatial patterning analysis, and using a sliding scale of trees per circle by quadratic mean diameter.