The effects of retention harvests on forest structure and bat populations in Ohio oak-hickory forests
Marne A.Titchenell, MS
Advisor: Stan Gehrt
Thesis: The effects of shelterwood harvests on bat populations and forest structure in Ohio oak-hickory forests
Forest management practices, such as harvesting, can greatly influence bat habitat relationships. Such practices can affect the microclimate and physical structure of the forest, foraging opportunities, and the availability of roost sites and prey. Research in eastern forests is needed to provide managers with the knowledge and skills to properly and effectively manage for bats and their habitat while still achieving forest management goals. One of these goals is the restoration of declining oak communities with regeneration methods, such as shelterwood harvests. This research examined bat activity responses to initial shelterwood harvests with different retention levels (50% and 70%) of the original basal area.
Bats were acoustically monitored and captured by the use of mistnets in the summer of June 2006 through August 2006 in harvested and unharvested areas. Overall general activity differed (p = 0.004) among harvested and unharvested areas with the greatest amount of activity occurring within the harvested areas. There were no differences in overall bat activity between different retention levels. Red bats (Lasiurus borealis), big brown bats (Eptesicus fuscus), and silver-haired bats (Lasionycteris noctivagans) were detected most in the harvested areas, and had low activity in the unharvested areas. Red bats, big brown bats, and silver-haired bats were detected equally in the two retention levels. Eastern pipistrelles (Pipistrellus subflavus) and myotis (Myotis sp.) were detected equally among both retention levels and the unharvested areas. A method was developed to quantify the amount of volume of woody plant material vertically through the forest canopy. The results of this method were compared to overall and species bat activity. Overall bat activity decreased rapidly at volumes exceeding 148.4 meters per hectare (m3/ha) in the understory (0-3 meters (m) above ground). The probability of detecting a red bat decreased by 50% at volumes exceeding 1500 m3/ha in the understory to mid-canopy (3-6 m), while big brown and silver-haired bat activity was detected most when volumes at 3-6 m in height were less than 100 m3/ha. Activity rates of Myotis species and eastern pipistrelles were not sensitive to volume of obstruction at any level.
Use of additional forest characteristics such as number of snags is recommended. This research suggests that areas harvested for the purposed of restoring oak communities can provide valuable foraging ground for multiple species of bats. Bats require a diversity of landscapes, and harvesting prescriptions should allocate area of high structural density in additions to the land being harvested. This research provides a framework for the management of bat populations in southern Ohio, allowing a unique opportunity for additional rigorous research in the future.