Long-term monitoring of sudden oak death in Marin County and the East Bay HillsAuthor(s): Brice A. McPherson; Greg Biging; Maggi Kelly; David L. Wood
Source: Proceedings of the sudden oak death sixth science symposium. Gen. Tech. Rep. GTR-PSW-255. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 25-26.
Publication Series: General Technical Report (GTR)
Station: Pacific Southwest Research Station
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Prior to 2000 the etiology, effects on host trees, and possible consequences for northern California’s forests of the syndrome known as sudden oak death were unknown. We designed a plot-based study to address these issues and to set a baseline for future evaluations.
In March-April 2000 we established a total of 20 plots in two forested areas in Marin County: China Camp State Park [CCSP] (10) and Marin Municipal Water District [MMWD] (10). The host species monitored were coast live oak [CLO] (Quercus agrifolia) and California black oak [CBO] (Q. kelloggii) in both sites and tanoak [TO] (Notholithocarpus densiflorus) in MMWD. We employed symptom-based monitoring on every stem >2-cm DBH (1.37-m), twice per year through 2007, then once per year through 2015. Symptom categories were bleeding; bleeding plus ambrosia and bark beetle attacks; bleeding plus beetles plus Annulohypoxylon thouarsianum sporocarps; and death. Trees that died without these symptoms were classified separately. Between 2000 and 2015, asymptomatic CLOs (n = 683) decreased from 68.8% to 42.9% and mortality increased from 6.7% to 40.5%. For CBO (n = 52), asymptomatic trees declined from 82.7% to 47% and mortality increased from 1.9% to 40.8%. For TO (n = 132), the asymptomatic trees decreased from 62.9% to 21.9% and mortality increased from 6.1% to 62.3%. The percentages of symptomatic trees declined from 22.4% to 8.7% for CLO and 31% to 15.9% for TO.
Of the CLOs that were asymptomatic in 2000 (n = 454), 22% were dead with SOD symptoms by 2015 and 10% were symptomatic. However, another 14% were in remission, which we define as cessation of bleeding for at least three years prior to 2015 in a previously symptomatic tree (in the absence of beetle attacks). Although the long-term durability of remission is not known, our previous estimates of CLO infection levels did not recognize the remission category.
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CitationMcPherson, Brice A.; Biging, Greg; Kelly, Maggi; Wood, David L. 2017. Long-term monitoring of sudden oak death in Marin County and the East Bay Hills. In: Frankel, Susan J.; Harrell, Katharine M., tech. coords. Proceedings of the sudden oak death sixth science symposium. Gen. Tech. Rep. GTR-PSW-255. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 25-26.
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