Fire, drought and flooding rains: The effect of climatic extremes on bird species’ responses to time since fire (2021) Connell et al., Diversity and Distributions, https://doi.org/10.1111/ddi.13287

The Crux

Both bushfires and extreme climate events are capable of shaping not only habitats, but also the number of different species that inhabit them. Yet the interaction between these phenomena can be equally important. For instance, an extreme flood or drought could have a very different impacts on a forest depending on how recently that forest was burned by fire. If a fire tore through recently, an extended period of drought may finish off species already under stress, yet if there has been a longer period of time since the last fire, the ecosystem may be able to tolerate a drought.

Given that climate change is increasing the occurrence of both extreme climate events and bushfires, it’s better to start investigating the effects of these interactions sooner rather than later. This week’s authors looked at the interaction between the two phenomena in south-eastern Australia, an area whose wildlife has come under a lot of pressure recently.

What They Did

The researchers used data from surveys at 180 sites across south-eastern Australia. The surveys were conducted during three different climatic periods, once during a massive drought from 2006-2008 (the Big Dry), one during a large rain event in 2011 and 2012 (the Big Wet) and another after the large rain event (Post Big-Wet).

The authors looked at both the occurrence and richness of bird species present at the different sites, and compared how they were related to the length of time since the last fire occurred in the area. They also checked to see how this comparison differed across the three climatic periods.

Did You Know: Backburning

Prescribed burns of areas during times of the year when fires are more controllable and unlikely to spread are a common fire prevention technique in much of the world. It rids the area of fuel which can make fires that occur at hotter and drier times of the year much worse. Conversely, fire suppression regimes can lead to a build-up of fuel over the years, which hasn’t helped California (see this great article by Lara Veylit).

What They Found

Species occurrences and richness was much higher during the Big Wet than during the Big Dry, with many species able to maintain their increases into the Post Big-Wet. The species that showed an increase in occurrence during the Big Wet were for the most part resident species: species that inhabit the area permanently rather than moving around from place to place (which are known as nomadic species).

Surprisingly, time since fire didn’t seem to have any effect on ecosystems during the Big Wet or Big Dry. Yet it had a noticeable effect on species richness and occurrence during the Post Big-Wet, with higher species richness occurring in areas that hadn’t recently experienced fire. Many individual species also responded similarly during the Post Big-Wet, with their chance of occurring significantly higher if an area hadn’t been burnt recently. Surprisingly, time since fire didn’t seem to affect ecosystems during the Big Dry or Big Wet.

Problems

One of the big problems with a study like this is that it’s hard to tease effects apart. Each site has a different time since fire, but are differences in an ecosystem down to time since fire, or other specific characteristics of that ecosystem? It’s something that’s difficult to account for, though the authors did attempt to do so by looking at differences across landscape types as opposed to individual sites.

So What?

The paper is further proof of complicated relationships between fire and other extreme climatic events. With summers in many parts of the world becoming longer, the time for conducting prescribed burns to lessen the risk of severe fires is shortening. Knowing when to conduct these burns therefore becomes key, as is knowing where the risk isn’t worth it. If an ecosystem has experienced fire too recently, or is in the midst of a climatic event that could make even a small fire a disaster for local species, perhaps it’s best to wait.

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Sam Perrin is a freshwater ecologist currently completing his PhD at the Norwegian University of Science and Technology who regrets nothing except perhaps having seen the movie Cats. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.

Title Image Credit: Terri Sharp, Pixabay licence, Image Cropped