Changes in gambel oak densities in southwestern ponderosa pine forests since Euro-American settlement

摘要

Densities of small-diameter ponderosa pine (Pinus ponderosa) trees have increased in southwestern ponderosa pine forests during a period of fire exclusion since Euro-American settlement in the late 1800s. However, less well known are potential changes in Gambel oak (Quercus gambelii) densities during this period in these forests. We reviewed published literature to summarize changes in oak density in ponderosa pine forests over the past 140 years and evaluated the possibility that large-diameter oaks have decreased in density. All nine studies examining oak density changes found that densities of small-diameter oaks have escalated. Increases ranged from 4- to more than 63-fold. These increases are comparable on many sites to those of ponderosa pine. Studies in northern Arizona, which analyzed cut stumps and past and present diameter distributions, did not find strong evidence that large-diameter oaks on average have declined in density. However, since oak cutting varied across the landscape, this important question needs additional study. Actively or passively managing Gambel oak requires decisions about desired future conditions and how to attain them. A possible contention for passive management—that the overall abundance of oak has decreased—is not supported by research published to date.