Temperatures below leaf litter during winter prescribed burns: implications for litter-roosting bats

Abstract

Some bat species, including eastern red bats (Lasiurus borealis), roost for short periods beneath leaf litter on the forest floor during winter in the south-eastern USA, a region subjected to frequent fire. The variability in fuel consumption, the heterogeneous nature of burns, and the effects of litter and duff moisture on forest-floor temperatures during winter burning could influence potential survival for bats beneath the leaf litter if they are unable to escape on-coming flames. We measured temperatures below leaf litter in 64 south-slope plots during nine controlled burns in the Ouachita Mountains of Arkansas to determine the probability of survival. Maximum temperature recorded under leaf litter at each plot averaged 292°C (±20 s.e.) and ranged from 10 to 717°C. Only three (5%) of the plots experienced temperatures that were deemed survivable (<60°C sustained for 60 s) during burns on warmer winter days (air temperatures 15.0–26.1°C). Temperatures below the leaf litter measured just before the arrival of fire (average = 19.6°C) suggested that if bats were roosting in plots they would have been in shallow torpor, which would have enabled faster escape from approaching flames. Burning during the warmer periods of winter (e.g. ≥15°C) and during afternoons could potentially improve survival by bats roosting under leaf litter by reducing arousal and escape times.