A new paper from the Mallee Fire and Biodiversity Team, led by Angie Haslem, has been published online in the journal Biological Conservation. The article tackles a very tricky issue for fire ecology generally, and fire in the mallee more specifically; how does fire history – including both time since the last fire (‘time-since-fire’) and the time between consecutive fires (‘inter-fire interval’)- influence the availability of resources critical to fauna.
The focus of the paper is on tree hollows. Tree hollows in many ecosystems are critical to a range of fauna, including birds, bats and arboreal mammals (see this book for further info). Fire has the capacity to massively alter the distribution of hollows, either by incinerating hollow-bearing trees, or by promoting hollow growth in trees that persist following fire.
We found that time-since-fire is a strong driver of hollow availability, with live stems < 40 years since fire being unlikely to possess hollows, whereas hollow availability in dead stems peaked around 50-60 years for basal hollows and 20-30 years for canopy hollows. This insight complements previous work (also led by Angie) published in the Journal of Applied Ecology.
In my opinion, the most interesting insight was the role of inter-fire interval on hollow availability. It is very tricky to estimate inter-fire interval in systems like the mallee, where satellite images capture only a fraction of the fire history of the system. Thus, in order to estimate inter-fire interval in the absence of satellite imagery, novel methods are required. Angie used a previously developed model of stem growth in mallee trees to estimate the age of dead stems presumably killed in the preceding fire event, as a way to estimate how long a site had gone without fire prior to the most recent fire. Using this method, we found that inter-fire interval had a strong effect on the density of hollows at a site, with areas that had an inter-fire interval of >50 having the greatest density of hollows in dead stems.
What does this mean? These results suggest that infrequent fire is likely to promote the density of hollow-bearing stems in mallee environments. That is, sites that are very old (> 50 years since fire) and have had experienced long periods of time between fires (i.e. prior to the most recent fire) are likely to be critical for hollow dependent fauna.
If you would like a reprint feel free to request one from Angie (A.Haslem@latrobe.edu.au)