Boyles and Aubrey, 2006 (Forest Ecology and Management)
RESEARCH BRIEF #3
A summary based on the following publication:
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MANAGEMENT IMPLICATIONS
Evening bats strongly preferred roost trees within burned areas compared to unburned areas
Repeated prescribed fire created open foraging conditions which are
favorable to lesser agile bats
Increased abundance of dead trees may benefit other snag-roosting bat species such as Indiana bat (Myotis sodalist)
In this study the authors sought to determine if evening bats (Nycticeius humeralis), a tree cavity-roosting species, exhibit a preference for burned versus unburned forests in roost-site selection. In addition, they sought to better understand the forest characteristics which influence roost tree selection. Fire is frequently prescribed to restore and/or maintain natural forest ecosystems in North American eastern deciduous forests. Fire is known to alter forest characteristics which influence bat roosting preference in the following manners: tree mortality, pathogen susceptibility, and light penetration. Many studies have investigated forest-dwelling vertebrate responses to prescribed fire, however, none reported on the effects of fire to forest-dwelling bat roosting habitat.
This study was conducted at Missouri Department of Conservation (MDC) managed Drury Conservation Area in southwestern Missouri. Beginning in 1999 MDC applied prescribed fire biennially to approximately half of the suitable (forested) evening bat roosting site area to restore glades and oak-hickory woodlands. Using standard capture and radiotelemetry techniques the location of roosting trees of twenty-three evening bats (11 males, 12 females) were identified. The study occurred year-round so to include roost trees used during winter and summer months by males and females in all reproductive stages. Bats were captured mainly in the fire break between the burned and unburned area in order to minimize capture location bias. Canopy light penetration (CLP) and canopy tree density were measured for both burned and unburned areas.
Sixty-three roost trees used by these 23 bats were identified over a time period slightly longer than one year. All roost sites were within the prescribed fire area, and all except one were greater than 50 meters from any forest edge. Canopy light penetration was significantly higher in the burned forest areas, and overstory tree density was greater in the unburned forest areas. The density of dead trees was not significantly different between treatments, though the proportion of dead trees relative to live trees was greater in burned areas. Evening bats displayed an overwhelming preference for roost trees located within prescribed fire managed forests. The authors attributed this preference to several contributing factors. First, fire increased the abundance of dead trees in some forests, therefore increasing the number of tree cavities available for roosting. Second, high light exposure is known to improve roost suitability; high light exposure in the interior of the forest may increase the overall area available suitable roosting habitat. This increase in suitable roost trees may promote bats to roost closer to preferred forage areas, decreasing commuting distance (in turn decreasing energy expenditure and predation exposure). Third, repeated prescribed fire reduced the regeneration of the sapling layer in forests, creating preferable foraging conditions for the lesser agile evening bat. Lastly, the major food source of evening bats, beetles, were found in greater species richness in burned forests compared to unburned forests (see Saint-Germain et al., 2004).
Managing forests with prescribed fire: evening bats
These results were also encouraging for the conservation of the federally endangered Indiana bat (Myotis sodalist). This species is known to roost in the exfoliating bark of dead and dying trees, of which there are more in fire managed hardwood forests. The authors cautioned that because this study only included six years since the initiation of burning, potential negative effects of long term burning may not be captured. The authors also noted that additional research is necessary to understand possible negative side effects on different bat species. For example, frequent burning could have negative effects on leaf litter roosting bat species such as eastern red bat (Lasiurus borealis).
Justin G. Boyles and Doug P. Aubrey, Forest Ecology and Management 222 (2006) 108-115
FOR FURTHER READING
The Oak Woodlands and Forests Fire Consortium seeks to provide fire science to resource managers, landowners, and the public about the use, application, and effects of fire in the region. www.oakfirescience.com
This research brief was funded by The Joint Fire Science Program. http://www.firescience.gov/
