Early settlement forest structure in Black Hills ponderosa pine forests

An ecological and management paradigm in ponderosa pine (Pinus ponderosa) forests is that historically recurrent surface fires maintained open forest stands dominated by large, old trees. Land use that accompanied Euro-American settlement in the late 1800s included timber harvest and fire cessation that resulted in loss of larger trees and increased tree density. Here we reconstruct basal areas, densities, ages, and sizes of larger trees ca. 1900 before initial tree harvest from 112 ponderosa pine stands in the Black Hills of the northern Great Plains. Reconstructed large tree basal area (BA) averaged 15.8m2ha−1, although there was a great deal of diversity in density. Approximately 35% of all plots contained 0–10m2ha−1 large tree BA but seven plots (∼6%) contained >40m2ha−1 large tree BA. Significant differences were found between plots at both local and broad scales. We found no significant differences in BA related to moisture gradients. There also was no significant difference between average BA of the historical and current forests, although historical tree stocking was dominated by larger trees than those present today. Current BA from the Black Hills National Forest Resource Inventory System averages 21.2m2ha−1, ranging from 0 to 49.5m2ha−1. Historical ponderosa pine forests in the Black Hills consisted of a diverse landscape mosaic that varied from non-forested patches and open stands of few large trees to quite dense stands with many similar-sized and -aged trees. Results largely support previous findings of changes in forest structure in ponderosa pine forests in response to timber harvest and loss of historical fire regimes, although the historical Black Hills landscape apparently contained a greater range of structural variability than ponderosa pine forests of the southwestern US. Our results support restoration of heterogeneity in landscape structure to enhance species habitat requirements and promote ecological resiliency.