PARENT SESSION
Oral Session # 33: Pathogens, Toxins, and Disease II: Plants.
Presiding: A Davelos
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 201.
White pine blister rust, fire and long-term demographic trends of sugar pine in the Sierra Nevada.
van Mantgem, Phillip *,1, Stephenson, Nathan1, Keifer, MaryBeth2, Keeley, Jon1, 1 U.S.G.S., Western Ecological Research Center, Three Rivers, CA2 National Park Service, Three Rivers, CA
ABSTRACT- An exotic pathogen, white pine blister rust, has caused declines in five-needled pines throughout western North America. While the range and severity of white pine blister rust infection are relatively well known, long-term demographic data that document the effects of the disease are rare. Simultaneously, fire exclusion may reduce recruitment opportunities for these shade-intolerant pines. Fire exclusion has also allows high fuels accumulations, making it unclear how affected populations will respond to the reintroduction of fire. We present population trends from 1,854 unburned and 321 burned sugar pine (Pinus lambertiana) individuals over 5-15 years at several burned and unburned sites at Sequoia and Yosemite National Parks. Populations are declining at most unburned sites (
range: 0.82-1.04), and bootstrapped confidence intervals of did not provide unequivocal evidence for population growth or stability at any site. Retrospective analysis suggests that declines are primarily a result of poor recruitment, although it is not clear whether small tree mortalities are most closely tied to biotic attacks or resource competition. Data from 16 prescribed fires showed that fire caused sharp, but transitory, increases in tree mortality, which does not appear to affect long-term population viability. Our models suggest sugar pine will not become extinct at any of our sites within 50 years. Nevertheless, some populations show rapid rates of decline for a long-lived species, and additional stressors, such as increased pathogen virulence, or climatic change, could accelerate the rate of decline.
Key words: fire exclusion, population decline, disease , Pinus lambertiana