Fire And Climatic Extremes Shape Mammal Distributions In A Fire-Prone Landscape

Ryan Duffy has sent me a paper recently published in Diversity and Distributions.  It is too long and detailed to include here but most thought provoking. The authors include Susannah Hale who spoke to us earlier in the year. If you would like to read the whole document I can email it to you, but I am giving you the abstract and then a few more details.
Fire and climatic extremes shape mammal distributions in a fire-prone landscape

The Grampians Fire and Biodiversity Project is a collaboration between Deakin University, Charles Sturt University and Parks Victoria. The team is interested in the ability of land management to enhance the capacity of the Grampians ecosystem to cope with and recover from changes in climate
and disturbance regimes.

ABSTRACT
Aim: Extreme climatic events and large wildfires are predicted to increase as the world’s climate warms. Understanding how they shape species’ distributions will be critical for conserving biodiversity. We used a 7-year dataset of mammals collected during and after south-east Australia’s Millennium Drought to assess the roles of fire history, climatic extremes and their interactions in shaping mammal distributions.

Location: Grampians National Park, south-eastern Australia.

Methods: We surveyed mammals at 36 sites along a ~50-year post-fire chronosequence in each of the 7 years. We modelled ten mammal species in relation to fire history, productivity and recent rainfall. Next, we examined the consistency of species’ fire response curves across each of three climatic phases relating to the Millennium Drought. Finally, we identified the optimal distribution of fire ages for small and medium-sized mammal conservation in each of the three climatic phases.

Results: The majority of species were influenced by fire history, and all native species were negatively associated with recently burned vegetation. Seven of ten species responded positively to the end of the Millennium Drought, but six of these declined quickly thereafter. Species’ responses to fire history differed depending on the climatic conditions. However, the optimal distribution of fire-age classes consistently emphasised the importance of older age classes, regardless of climatic phase. This distribution is in stark contrast to the current distribution of fire ages across the study region.

Main conclusions: Mammals in the study region face an uncertain future. The negative impact of drought, the short-lived nature of post-drought recovery and, now, the possibility of a new drought beginning forewarn of further declines. The stark contrast between the optimal and current fire-age distributions means that reducing the incidence of further fires is critical to enhance the capacity of native mammal communities to weather an increasingly turbulent climate.

Some of the details: We used a large dataset on native mammal communities spanning seven consecutive years (2008–2014). Our study region, the Grampians National Park, has recently experienced strong interactions between fire and climatic extremes, including three large fires (ranging from 35,000 to 85,000 ha) since 2005, and severe drought followed by record-breaking rains. The consecutive multiyear nature of our dataset allows us to investigate the effects of fire and rainfall simultaneously. The region has a diverse range of small-and-medium-sized mammals, including two monotremes, 14 marsupial species and six rodent species (two of which are introduced). Using this dataset, we address four questions of fundamental importance to both ecological theory and applied ecology in fire-prone regions:

  1. Does fire history drive mammal abundance and occurrence within this region, and if so, over what time frames?
  2. Do climatic extremes affect mammal occurrence, and is there evidence for boom and bust phases within this temperate ecosystem?
  3. Do fire history and climatic extremes interact to shape species distributions?
  4. What is the optimal distribution of fire-age classes for mammal conservation and does this differ under different climatic phases.

Site selection and description: Thirty-six study sites were selected within the Grampians
National Park . Sites were initially selected to examine the consequences of a large wildfire on the mammal community. The large wildfire occurred in 2006 and burned ~85,000 ha (~50% of the park). Sites were chosen to encompass areas that were burned (n = 19) and unburned (n = 17) . Sites not burned in 2006 represented a post-fire age gradient of ~50 years. Sites were spread across the park and were predominately in heathy woodland and sand heathland and were constrained by a further four factors: (1) all sites were located at the same elevation to account for the influence of elevation on rainfall; (2) all were established within an intensive fox baiting area, maintaining consistent management practices; (3) all sites were accessible via the road network for time efficiency; and (4) all sites were established with a distance of at least 2 km between them, increasing site independence.

Implications and conclusions: The strong association between mammals and rainfall means that a future with increasingly intense and longer-term droughts could imperil many species. In addition, large-scale wildfires have established the majority of the ecosystem in an early successional period. This trend of larger, more frequent and intense fires is predicted to continue under scenarios of climate change (Intergovernmental Panel on Climate Change, 2013). Fires occurring during protracted droughts will be particularly damaging and have the potential to drive species towards local extinction. Fire management must aim to burn strategically to minimise the size of these fires and retain as larger areas as possible in older successional states, particularly during drought.

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FOGGS have a policy of financially supporting students doing research in the Park, and of inviting them to share their knowledge with us and the public. As Ryan observed to me as he gave me this paper, it will be fascinating to see what results the next trapping programme will reveal, after such a lovely wet winter. It is so good that this kind of longitudinal study is happening, and that such a good partnership is in place between our rangers and the Universities.

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