Long-term trends in coast live oak and tanoak stands affected by Phytophthora ramorum canker (Sudden Oak Death)
| Authors: | Tedmund J. Swiecki, Elizabeth Bernhardt |
| Year: | 2010 |
| Type: | General Technical Report |
| Station: | Pacific Southwest Research Station |
| Source: | In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M. 2010. Proceedings of the Sudden Oak Death Fourth Science Symposium. Gen. Tech. Rep. PSW-GTR-229. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 207-209 |
Abstract
Permanent plots were established in 2000 to examine how tree and site factors affect risk of Phytophthora ramorum stem canker (sudden oak death [SOD]) and determine how affected stands change over time due to disease. P. ramorum canker was prevalent in the sampled coast live oak (Quercus agrifolia) or tanoak (Lithocarpus densiflorus) stands in 2000. In September of each year from 2000 through 2008, we collected data on P. ramorum symptoms, tree condition, tree failures, regeneration, and various other factors in 150 circular plots (8 m radius) at 12 locations in Marin, Sonoma, and Napa Counties.Disease development patterns over time differed between tanoak and coast live oak populations in the study (fig. 1). The increase in disease incidence between 2000 and 2008 was greater for tanoaks (31 to 49 percent) than for coast live oak (23 to 33 percent). Disease incidence in coast live oaks increased strongly from 2005 through 2007. This increase was associated with abundant late season rains that provided favorable conditions for disease spread in spring 2005 and spring 2006. Tanoak showed a less much pronounced increase in disease incidence for these two years. Based on time lags between favorable conditions for infection and the appearance of visible symptoms, most coast live oaks had latent periods from 0.5 to 1 year, whereas the minimum latent period in tanoaks was commonly about a year.