Interior Chaparral Shrubland

Abstract

Interior Chaparral Shrubland covers more area on the mountains and plateaus of the American Southwest than any other shrubland. It is dominated by broad-leaved, evergreen shrubs with dense, compact crowns and generally extensive, deep root systems. Interior Chaparral Shrubland overlaps the elevational range of Pinyon-Juniper vegetation, occurring below Ponderosa Pine Forest and above desert scrub or semi-desert grassland. The primary natural disturbance is infrequent, high-severity fire. Major anthropogenic disturbances are livestock grazing and fire management; others are modern climate change, invasive species, recreation, and nearby land use. Vegetation dynamics are dominated by rapid regrowth after fire. This is facilitated by sprouting from below-ground structures and by fire-stimulated germination of seeds in the seed bank. Some stands are successional, particularly in the transition with Ponderosa Pine Forest. Historical conditions are poorly known, but Interior Chaparral Shrubland has been stable in its regional distribution. Herbaceous cover likely was reduced by intensive livestock grazing, and shrub cover increased by fire exclusion. The claim that shrubs of Interior Chaparral Shrubland expanded into other types of vegetation because of livestock grazing is unsupported. Vegetation dynamics are illustrated in a nested, three-tiered set of conceptual models. Key conclusions and challenges for researchers and land managers are summarized.