Pre-epidemic mortality rates for common Phytophthora ramorum host tree species in California

Abstract

Understanding the impacts of Phytophthora ramorum on forests will require knowledge of pre-disease distribution, abundance, and rates of change for affected species. This study estimated pre-epidemic mortality rates for nine common host tree species: bigleaf maple (Acer macrophyllum), California bay laurel (Umbellularia californica), California black oak (Quercus kelloggii), canyon live oak (Quercus chrysolepis), coast live oak (Quercus agrifolia), Douglas-fir (Pseudotsuga menziesii), madrone (Arbutus menziesii), coastal redwood (Sequoia sempervirens), and tanoak (Lithocarpus densiflorus) using inventory data from 1981 to 1984 and 1991 to 1994 statewide inventories of private (and some public) forest land. Mortality rates that were developed represent the average annual mortality for trees that were at least 12.5 cm in diameter at 1.4 m above the ground (dbh) at the time of the first (1981-1984) inventory. Natural mortality for all trees was estimated at 0.5 percent of trees per year, with rates for individual host species ranging from 0.1 to 0.6 percent. Overall, growth exceeded natural mortality and harvest for most host species between 1981 to 1984 and 1991 to 1994. Tanoak, the most numerous tree species in the quarantined counties, increased in volume and number of trees by more than 15 percent over the decade.

Parent Publication

• Proceedings of the sudden oak death second science symposium: the state of our knowledge

Citation

Barrett, T.M. 2006. Pre-epidemic mortality rates for common Phytophthora ramorum host tree species in California. In: Frankel, Susan J.; Shea, Patrick J.; and Haverty, Michael I., tech. coords. Proceedings of the sudden oak death second science symposium: the state of our knowledge. Gen. Tech. Rep. PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 371-378