Second Science Symposium
January 18 - 21, 2005
Incidence of Phytophthora ramorum, P. nemorosa and P. pseudosyringae in Three Coastal California Forest Communities
Shannon K. Murphy and David M. Rizzo, Department of Plant Pathology, University of California, Davis, CA 95616; (530)754-9894; email@example.com
Phytophthora ramorum (Pr) is well established
over approximately 450 km of forests along the California coast. In the
course of research on this emerging pathogen, two other aerial Phytophthoras,
P. nemorosa (Pn) and P. pseudosyringae (Pps), were discovered.
Little is known about the ecology and biology of these other species and
how they interact with Pr. Preliminary research has found that Pn and
Pps have similar host ranges and cause similar disease symptoms as Pr,
however do not appear to cause landscape level mortality of oaks (Quercus
spp) and tanoak (Lithocarpus densiflorus) as does Pr. A
plot study was established to determine the distribution and incidence
of Pr, Pn and Pps in coastal forest communities, and relate pathogen presence
to community, structural, and environmental variables. 120 circular 500
m2 plots were set up at ten sites within the known range of Pr in Alameda,
Contra Costa, Marin, Mendocino, Napa, Santa Cruz, and Sonoma counties.
Field plots were established during the summer months of 2001 and 2002
and re-sampled in the spring and summer of 2004. Six of the sites were
in California state parks, three were in county or regional parks, and
one was on a private property protected with a conservation easement.
Three types of native forest communities were surveyed: coast redwood,
and two associations of the mixed evergreen forest, oak-bay-madrone and
tanoak-madrone-live oak-Douglas-fir forests. Plots were located along
elevational gradients proceeding perpendicularly from river valleys toward
ridge tops, with three plots along four transects at each site. Plot selection
was based on aspect, plant community, and minimized human disturbance,
rather than presence of Phytophthora species. Each plot was evaluated
for plant species composition, forest structure and environmental variables,
and incidence of aerial Phytophthora species.
We found these three Phytophthora species to occupy
similar ecological niches within the same plant communities. As with previous
studies on Pr, bay laurel was a significant correlate with the occurrence
of all Phytophthora species. Results from this study provide
additional information about the distribution of Pr, including examination
of location and intensity of SOD within state and regional parks, and
within east bay counties where Pr plots had not previously been established.
This is the first study to examine the ecological associations between
these three Phytophthora species, across a wide geographic distribution
and within several plant communities.
| 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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