Bat activity and insect availability in early successional forests: a preliminary analysis

1. Fig. 1 Community interactions model Fig. 9 Bat passes per hour (pph) by site type. Means are based on 12 nights in the 0-1 year old category and 8 nights in all others. Fig. 10 Relative insect abundance by site type. Means are based on two samples per site type; bars represent mean dry mass by insect group and circles represent average percent of total mass. 3.3 ±1.0 Fig. 11 Vegetation density by vertical height interval and site type. Abstract Recent research in the United Kingdom found significant differences in bat use of organic and conventional agricultural land. The elucidated link between vegetation management, insect communities, and bat foraging activity also could apply to managed timber lands. We investigated this potential link in forest stands managed under various regimes to test the hypothesis that bat activity is higher in sites with more plant and, therefore, insect diversity. We conducted this research in the Appomattox-Buckingham State Forest in central Virginia in June-August 2006. We sampled 9 sites representing a continuum from young (0-1 year-old) released loblolly pine plantations to oak shelterwood sites. • Results, continued • While these preliminary results should be interpreted with caution, we look forward to exploring in more detail the following trends: • In comparing the three pine habitat types, there is a decrease in observed bat activity as plantations age (Fig. 9). • Insect biomass was similar in three habitat types, but biomass was much greater in the youngest of the habitats (Fig. 10). • Vegetation density and overall height increased with site age (Fig. 11). Insect Sampling Insect samples were collected using UBLTs with photoelectric switches running on 12-V deep-cycle marine batteries (Fig. 5). Insects were collected in large glass jars that contained an insect kill strip. We retrieved the jars each morning, transferred the specimens to freezer bags, and froze specimens for later analysis. Prior to processing, each sample was dried for 24 hours at 60°C and transferred to plastic storage containers along with a desiccant. Dried insects were separated into 3 groups (Lepidoptera, Coleoptera and other) using magnifying glasses and a dissecting microscope. We separated Lepidoptera and Coleoptera because these orders made up the bulk of our samples and are known to be important bat prey. We weighed each group to determine biomass by group and for the complete sample. Sampling Arrays In each site, we established an array with one bat detector and 4 Universal Black Light Trap (UBLT; BioQuip Products, Inc.) locations (Fig.2). Bat Sampling Bat detector systems [with Anabat II detector and ZCAIM (Titley Electronics) housed in a plastic cooler with 4” PVC elbow joint; after S. Amelon] recorded data between 1930 and 0630. Each bat detector system was placed on a stump for elevation from the ground, and the PVC elbow was oriented to provide the microphone with a clear, unobstructed detection cone (Fig. 3). We used AnaLook to view the data and count number of passes per hour (Fig. 4). Bat activity and insect availability in early successional forests: a preliminary analysis • Discussion • In relating our preliminary results to our proposed model (Fig. 1), some predictions paralleled observed results while others did not. • We predicted a positive relationship between vegetation density and insect abundance (i.e., biomass). However, the sites with the greatest insect abundance were those with the lowest vegetation density. • We predicted a positive relationship between insect abundance and bat activity. Our preliminary results support that relationship. However, the mediating factor of vegetation clutter on foraging activity is one that we will explore in more detail. Introduction Forests of the southeastern U.S. are changing rapidly, both in terms of forest composition and extent of forest cover (Wear and Greis 2004). Compositional changes are being driven by increasing conversion to pine (Pinus sp.) plantations and increasing management intensity (Siry 2002, Wear and Greis 2004). Concurrent to changes in composition, forest cover is decreasing as a result of urbanization and sprawl associated with human population growth (Wear 2002). Moreover, the nature and extent of impacts of global climate change on Southern forests are largely speculative (Moore et al. 2002), though further changes in composition and coverage are expected. Questions related to the impacts of these changes on wildlife species are of great conservation interest and management relevance. Highly mobile species with large home ranges and complex habitat requirements, such as bats, may be especially vulnerable to increasing human modification of landscapes. However, the impacts of such modifications on bat species are poorly understood (e.g., Tibbels and Kurta 2003). These relationships were recently explored by researchers in the U.K. who found significant differences in bat foraging activity in organic and conventionally managed agricultural land (Wickramasinghe et al. 2004). The differences in bat foraging were related to differences in insect abundance in the sites (Wickramasinghe et al. 2003), which in turn was directly related to intensity of vegetation management and/or control (Wickramasinghe et al. 2004). Vegetation We quantified vegetation density using a density board (3 m x 10 cm; Fig. 7) at two vegetation sampling points in each study site (Fig. 2). We photographed the board from a distance of 4 m in each of the four cardinal directions. In the lab we then quantified percent of vegetation density using photographs. Fig. 4 Bat calls Results 8-10 year old pine (released) 3-4 year old pine (not released) 0-1 year old pine Regenerating oak shelterwood • Future Directions • In continuing the analysis of the data collected this summer, we will • Conduct a detailed examination of the full data set using the Information Theoretic approach to linear modeling. • Analyze fecal pellets collected at our study sites and attempt to relate their contents to insects collected in the UBLTs. • In future field seasons, we will • Incorporate multiple sampling arrays per site in different microhabitats to better understand bat activity. • Include more mature pine sites to extend the continuum and assess the trends in insect availability and bat use. • Finally, in the long term we seek to • Provide information to add to our understanding of how wildlife species use intensively managed forest systems. • Relate bat activity in early successional habitats to the better understood avian use of those habitats to build a more holistic view for conservation and management decisions, particularly as they relate to management of sites within broader landscape contexts. 4.22 ± 3.85 Overall mean pph ± SD 7.06 ± 7.96 3.13 ± 2.24 3.91 ± 2.46 Kathryn M. Womack and Alix D. Fink Department of Biological and Environmental Sciences Mean mass per sample ± SD (g) 11.6 ±2.6 3.6 ±1.3 3.6 ±1.6 Methods Study Area The Virginia Piedmont region provides an interesting context for addressing research questions related to habitat use in actively managed forests. Virginia’s Piedmont is still largely forested (>80% forest cover in some counties; Wear and Greis 2004), and it includes large extents of intensively managed pine forests. Additionally, in the next few decades the Piedmont region is expected to lose more forest cover than any other region in the Southeastern U.S. (Wear and Greis 2004). Our study area, the Appomattox-Buckingham State Forest (ABSF), encompasses over 19,000 acres within a largely forested landscape with industrial and other private landowners. The ABSF is managed by the Virginia Department of Forestry for multiple uses. In the ABSF, we selected 9 study sites representing a continuum from young (0-1 year-old) loblolly pine plantations to oak (Quercus sp.) shelterwood sites. Acknowledgements This research was supported by a Longwood University Faculty Research Grant. Additional in-kind and indirect support were provided by Longwood’s Department of Biological and Environmental Sciences and the Geographic Information Systems Laboratory, the Virginia Department of Forestry, and the Kennedy Tree Farm. We also thank the following individuals for their help and support: D. Horchler, T. Akre, M. Fink, E. Kinman, and S. Amelon. Overall mean % cover (n), max. height (m) 16.7% (16), 1.0 42.6% (15), 1.9 47.7% (6), 2.2 77.3% (6), 2.9 Literature Cited Moore, J.A., J. Bartlett, J. Boggs, M. Gavazzi, L. Heath, and S. McNulty. 2002. Abiotic factors in the Southern Forest Resource Assessment (D. Wear and J. Greis). Siry, J. P. 2002. Intensive timber management practices in the Southern Forest Resource Assessment (D. Wear and J. Greis). Tibbels, A. E. and A. Kurta. 2003. Bat activity is low in thinned and unthinned stands of red pine. Canadian Journal for Forest Research 33, 2436-2443. Wear, D. N. 2002. Land use in the Southern Forest Resource Assessment (D. Wear and J. Greis). Wear, D. N. and J. Greis. 2004. What we learned in the Southern Forest Resource Assessment (D. Wear and J. Greis). Wickramasinghe, L.P., S. Harris, G. Jones, and N.Vaughan Jennings. 2003. Bat activity and species richness on organic and conventional farms: impact of agricultural intensification. Journal of Applied Ecology 40, 984-993. Wickramasinghe, L.P., S. Harris, G. Jones, and N.Vaughan Jennings. 2004. Abundance and species richness of nocturnal insects on organic and conventional farms: effects of agricultural intensification on bat foraging. Conservation Biology 18:5, 1283-1292.