Managing Gambel oak in southwestern ponderosa pine forests: the status of our knowledge

Abstract

Gambel oak (Quercus gambelii) is a key deciduous species in southwestern ponderosa pine (Pinus ponderosa) forests and is important for wildlife habitat, soil processes, and human values. This report (1) summarizes Gambel oak's biological characteristics and importance in ponderosa pine forests, (2) synthesizes literature on changes in tree densities and fire frequencies since Euro-American settlement in pine-oak forests, (3) suggests management prescriptions for accomplishing various oak management objectives (for example, increasing diameter growth or acorn production), and (4) provides an appendix containing 203 Gambel oak literature citations organized by subject. Nine studies that reconstructed Gambel oak density changes since settlement in the late 1800s reported that densities of small oaks have escalated, with increases ranging from 4- to more than 63-fold. A possible argument for passive oak management, that overall oak abundance has decreased, is not supported by published research. Manipulating oak growth forms is one of the main means for managing oak and ecosystem components affected by oak. Published research has classified variants of three basic oak growth forms: shrubby thickets of small stems, pole-sized clumps, and large trees. Burning and cutting constitute major prescriptions for manipulating these growth forms, whereas pine thinning has most consistently increased oak diameter growth for promoting large oaks. Because of their high ecological value, large, old oaks should be retained in any management prescription. Sufficient research has been published on which to base some oak management prescriptions, but additional research on poorly understood aspects of oak's ecology is needed to refine and improve oak management.