Second Science Symposium
January 18 - 21, 2005
Pre-Epidemic Mortality Rates for Common Host Tree Species in California
Tara Barrett, Forest Inventory and Analysis, PNW Research Station, Forest Service, P.O. Box 3890, Portland, OR 97208; (503) 808-2041; firstname.lastname@example.org
Understanding the impacts of Phytophthora ramorum on forests requires knowledge of pre-disease distribution, abundance, and rates of change for affected species. This study estimated pre-epidemic mortality rates for common host tree species using inventory data from statewide inventories of private (and some public) forestland in 1981-84 and 1991-94.
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 at the time of the first (1981-84) inventory. Natural mortality for all tree species combined was estimated at one half of one percent of trees per year. When trees that were harvested or culturally killed were included, the mortality rate doubled to one percent of trees per year.
Species that are known hosts to Phytophthora
ramorum with sufficient sample numbers to estimate mortality included
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). In the 1990s, these host
species were estimated to predominate by basal area on more than 1.56
million hectares of forestland within the quarantined counties of Alameda,
Contra Costa, Humboldt, Marin, Mendocino, Monterey, Napa, San Mateo, Santa
Clara, Santa Cruz, Solano, and Sonoma.
| Coordinated by:
USDA Forest Service Pacific Southwest Research Station
University of California Integrated Hardwood Range Management Program,
Center for Forestry, Division of Agriculture and Natural Resources, and
California Oak Mortality Task Force
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