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Beetle Response to Seasonal Prescribed Fire in Blue Oak (Quercus douglasii) Woodlands of Big Chico Creek Ecological Reserve
ABSTRACT BEETLE RESPONSE TO SEASONAL PRESCRIBED FIRE IN BLUE OAK (Quercus douglasii) WOODLANDS OF BIG CHICO CREEK ECOLOGICAL RESERVE by Mark Louis Lynch Master of Science in Biological Sciences California State University, Chico Spring 2011 Fire is an integral component of terrestrial ecosystem processes. The timing, intensity and frequency of fires influence ecosystem responses throughout the world. Prescription burns have been widely reintroduced into fire-adapted systems in order to restore natural processes, control exotic species, and other unwanted vegetation. The majority of studies examining the effects of prescribed fire have predominately focused on vascular vegetation; largely ignoring species in higher trophic levels. Beetles occupy multiple trophic levels as consumers, serving as decomposers, herbivores, predators, and scavengers. In order to improve our understanding of arthropod responses to seasonal variation in prescribed fire, I examined the effects of spring (late wet-season) and fall (early wet-season) prescribed fires on ground cover structure (bare ground, leaf litter, plant stem density) and ground-dwelling beetle guilds in blue oak (Quercus Douglassii) woodlands of Big Chico Creek Ecological Reserve (BCCER), Butte County, California. The study was conducted on twelve quarter hectare (50 m x 50 m) sites. Ground cover and beetles were sampled pre-treatment in April and early May 2007, followed by burning four sites (spring treatment) in late May 2007. Four more sites were burned (fall treatment) in early November 2007, with the four remaining sites left unburned (control). Post treatment sampling of ground cover and beetles occurred in April and early May 2008. Burn Severity was similar between spring and fall burn treatments, but fall burns experienced the highest variability in burn severity between sties. Bare ground increased and leaf litter decreased significantly in both spring and fall burn sites. Plant stem density decreased in fall burns, but did not change in spring burns. Overall beetle density decreased in fall and spring burn sites, but the differences were not significant between treatments. Beetle density in fall burn treatments tended to be lower than spring sites, but the response may have been complicated by temporal recovery between fall and spring treatments. With respect to guilds, seed eaters showed a strong negative correlation to burn severity and bare ground but a positive correlation to leaf litter, suggesting bare ground was associated with vital resource losses. Fire prescription studies conducted in California most often implement fire treatments with the support of professional private/government fire crews allowing burns to take place in drier conditions than allowed by burn permits issued to the public. The differences in prescription timing between public burn periods and that allowed by professional fire crews may affect plant and animal species differently due to the phenology and activity of species present at the time of burn prescriptions. Although fires decreased beetle density, results of the study did not show wet-season burn timing (spring and fall burn prescriptions) to have a negative effect in ground-dwelling beetle assemblages. The decrease in plant stem density in fall burns but not in spring burn sites suggests burn timing influenced plant stem density response and could prove useful in land management planning. Thus, burn timing appears to have significantly affected plant response, but had minimal influence on beetle response; suggesting spring and fall burn prescriptions can be utilized as a management tool without a dramatic impact on beetle guild assemblages present.