Thermal Profiles of Chainsaw Hollows and Natural Hollows during Extreme Heat Events

SIMPLE SUMMARY: Loss of large hollow-bearing trees is a major threat to the persistence of wildlife in agricultural landscapes. To combat this problem, local governments, volunteer environmental organizations, and conservation groups increasingly carve artificial hollows (“chainsaw hollows”) in dead trees, yet little is known about their thermal profiles. We measured the thermal profiles of 13 natural and 45 artificial hollows in the central west of NSW, Australia, over the course of 2 summers. Maximum temperatures and daily temperature ranges within natural hollows and artificial hollows were similar in 2017–2018. During the January 2019 heatwave, temperatures inside chainsaw hollows in dead trees exceeded 35 °C for 6.2 consecutive days. Artificial hollows in dead trees provided little buffering from thermal extremes; when air temperatures peaked at 44.6 °C, hollow temperatures were only 2.4 °C cooler on average than ambient (range: 5.5 °C cooler to 1.0 °C hotter than ambient). Artificial hollows created in dead trees may therefore not provide suitable thermal conditions for hollow-dependent wildlife during hot summers. Thus, retention of large live trees, coupled with revegetation, is crucial for conserving hollow-dependent fauna in agricultural landscapes. ABSTRACT: Loss of hollow-bearing trees threatens many hollow-dependent wildlife. To mitigate this process, artificial chainsaw-carved hollows (CHs) are often created in dead trees, yet little is known about their thermal profiles. We measured temperatures inside 13 natural hollows (8 live and 5 dead trees) and 45 CHs (5 live and 40 dead trees) in the central west of NSW, Australia, over the course of 2 summers. Maximum temperatures and daily temperature ranges within natural hollows and artificial hollows were similar in 2017–2018. Hollow temperatures were lower in thicker-walled hollows than in thinner-walled hollows. During the January 2019 heatwave, temperatures inside CHs in dead trees exceeded 4–35 °C higher than the upper limit of the thermal neutral zone of sugar gliders—for 6.2 consecutive days (range 0–9 days). CHs in dead trees provided little buffering from thermal extremes; when air temperatures peaked at 44.6 °C, CHs in dead trees were on average 2.4 °C cooler than ambient (range: 5.5 °C cooler to 1.0 °C hotter than ambient). These results show that CHs created in dead trees may not provide suitable thermal conditions for hollow-dependent marsupials during summer heatwaves. Retention of large live trees, coupled with revegetation, is crucial for conserving hollow-dependent fauna in agricultural landscapes.