Mixed Conifer Forest

Abstract

Mixed Conifer Forest occurs in an elevational band below Spruce-Fir Forest and above Ponderosa Pine Forest. It has diverse stands reflecting elevation, topography, moisture availability, disturbance history, and successional state. Trees include ponderosa pine, Douglas-fir, white fir, quaking aspen, southwestern white pine, limber pine, blue spruce, and others. A primary driver of Mixed Conifer Forest has been fire. The historical, mixed-severity fire regime combined frequent, widespread, low-severity surface fires and infrequent, patchy, high-severity crown fires. Important anthropogenic disturbances are livestock grazing, fire management, modern climate change, invasive species, recreation, and nearby land use. Gap dynamics and succession are key vegetation dynamics. Historical conditions are poorly known. Forest density and basal area increased as a result of exclusion of fire, which began in the second half of the nineteenth century. At least some stands decreased in density and basal area during the twentieth century, apparently as a result of density-dependent factors and exogenous factors such as climate change. Fire exclusion also increased landscape homogeneity. Greater fuel loads and more continuous fuels have resulted in landscape-scale crown fires. Vegetation dynamics are illustrated in a nested, three-tiered set of conceptual models. Key conclusions and challenges for researchers and land managers are summarized.