Species composition varied selleck products substantially within habitat types between study areas for some metrics: white fir was much more abundant in Moist Mixed

sites in Chiloquin than Wildhorse, sugar pine was abundant only in the Dry Mixed in the Black Hills, and lodgepole pine was more abundant in the Wildhorse area. Stand structure on the Dry Mixed sites in the Black Hills was most strongly dominated by large trees (73 ± 6% of tph > 53 cm dbh). The wide range of values recorded across the landscape reflects the inclusion of more rare and extreme conditions than the narrower range indicated by the standard deviations and 95th percentile values that reflect the Selleck GDC 0449 preponderance of low-density forests dominated by large ponderosa pine trees as described in Section

3. Mean forest density has increased by more than 300% during the last 90 years, as measured by number of trees per hectare, and shifted toward a dominance of shade-tolerant species on mixed-conifer sites (Table 5). The increases in densities are due to increased populations of small diameter (15–53 cm) trees as there has been a substantial decrease in the densities of large diameter (>53.3 cm) trees (Table 5). The mean relative abundance of large trees as a proportion of total density has decreased by more than a factor of five and the percentage of the forest that supports at least 25 large-diameter tph (>53 cm dbh) has declined similarly (Table 5). Reductions in the abundance and proportion of large trees are universal on all habitat types. Changes in species composition as a proportion of density are more apparent on mixed-conifer sites. There has been only a modest increase in forest density (<20%) as measured by mean

stand basal area during the last 90 years, but it has been accompanied by a large reduction in basal area in large trees (>50%, Table 5). These statistics emphasize the dramatic change in overall stand structure from forests dominated by a few large trees to a much denser forest dominated by many small trees. The prevalence of low-density forests composed primarily of large-diameter ponderosa pines leads us to conclude that a disturbance Dichloromethane dehalogenase regime of frequent low- to moderate-severity fires was the dominant influence on the structure and composition of forests in this landscape for several centuries prior to the 1914–1922 inventory. The preponderance of low-density stands and pine dominance, even on the moister mixed-conifer sites, supports this inference. The structure and composition recorded 90 years ago is consistent with those of contemporary forests subject to frequent low- and moderate-severity disturbance (Stephens and Fulé, 2005, Stephens and Gill, 2005 and Collins et al., 2011).