The influence of habitat structure on insectivorous bat activity in montane ash forests of the Central Highlands, Victoria

Insectivorous Bats and Silviculture: Balancing Timber Production and Bat Conservation

“…The lack of recovery after 36 years in old regrowth coupes is consistent with a number of other studies where low activity persisted for more than 30 years after disturbance (Brown et al 1997;Adams et al 2009;Webala et al 2011), but differs from selective harvesting of wet sclerophyll forest in subtropical Queensland where recovery of bat activity was apparent in a site logged 33 years previously (de Oliveira et al 1999). It is important to note that none of these studies consider activity levels on tracks, riparian zones, or other areas of retention that potentially could ameliorate the effects of clutter from dense regrowth and loss of tree hollows.…”

“…This range in age is wide and likely spans considerable variation in above-ground habitat structure due to differences in the amounts of regeneration present; thus, a varied response by bats across studies and geographic locations should be expected. In montane eucalypt forests of south-eastern Australia, bat activity peaked in 165-year-old wildfire regrowth rather than in younger regrowth from clear-felling operations (Brown et al 1997). Unfortunately, the size and shape of clearcuts studied are rarely reported so an evaluation of the effects of cut size and shape on bat activity cannot be made.…”

Vegetation structure influences the vertical stratification of open- and edge-space aerial-foraging bats in harvested forests

“…Smaller canopy gaps could interfere with detection of above-canopy bats and may reduce the activity of bats in the gaps themselves. Like our study, increases in bat activity in older montane ash forests were suggested to be related to larger height differences between primary and secondary canopies and greater crown separation ratios in the primary canopy (Brown et al, 1997; ground-based vertically pointed detectors used). Conversely, a study of bat activity at different heights in mature and young pine plantations found the highest activity levels near the ground (2 m height) in mature plantations, where clutter was less than in young plantations.…”

“…Less horizontal space between boles and vertical space between crowns may have limited the flight activity of bats in the subcanopy and lower canopy of young regrowth, especially those guilds with lower frequency calls. Additionally, while canopy percentage cover did not vary between old and young regrowth, increased tree stem density in young regrowth might have been accompanied by a decrease in the size of gaps between the canopy tree crowns (Brown et al, 1997;Humes et al, 1999), although we did not measure this. All of our bat detectors were pointed towards vegetation gaps.…”

“…Conversely, in more open, usually older forests, we would expect to find evidence of activity by species from all bat foraging groups, as open space does not place limits on clutter-adapted bats (Fenton, 1990;Fullard et al, 1991;Saunders and Barclay, 1992). A number of studies have found differences in bat activity levels between forests of the same floristic type but different logging histories (Glass, 1993;Brown et al, 1997;Humes et al, 1999;Law and Chidel, 2002;. Most suggest that reduced clutter in older or thinned sites was a primary reason for increased activity.…”