Conifer encroachment in California oak woodlands

Abstract

California deciduous oak woodlands provide many ecological, cultural, and economic benefits, and often represent unique plant communities that harbor native rare and declining species. Oak woodlands have suffered substantial losses in area and ecological integrity in the post-settlement era due to land conversion and widespread fire exclusion. Remnant oak woodlands in many areas are undergoing further conversion to conifer forest as shade-tolerant, and often less fire-tolerant species invade and increase in abundance. This process, known as conifer encroachment, has been identified across the Pacific West; efforts to restore these ecosystems have increased in California over the past several decades. The process of conifer encroachment is known to occur in many ecosystems in California, but principally affects oak woodlands dominated or co-dominated by Oregon white oak (Quercus garryana) and California black oak (Quercus kelloggii). Encroachment proceeds through four phases including establishment, piercing, overtopping, and decadent; oak crown recession occurs by the third stage, after which oak mortality becomes abundant. The concomitant increased shading and needlecast from the conifers diminishes plant and animal biodiversity and ecosystem services, and alters fire regimes. We discuss encroached oak woodland structure and dynamics in northern California, identifying conifer species that have the capability and propensity under a fire-suppression management regime to invade and degrade remnant oak woodlands.

Parent Publication

• Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world

Citation

Cocking, Matthew I.; Varner, J. Morgan; Engber, Eamon A. 2015. Conifer encroachment in California oak woodlands. In: Standiford, Richard B.; Purcell, Kathryn L., tech. cords. Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world. Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 505-514.