Fire in the foothills

Fire regimes and environmental gradients shape the distribution of forest wildlife

A typical scene in the foothill forests of Victoria. In the morning mist this patch of woodland doesn’t look particularly fire prone but the blackened trunks, open canopy and epicormics buds (leaves sprouting from the main tree stem) suggest a major fire has passed through here recently. Indeed, this image was captured some 15 months after large wildfires seared parts of central Victoria. The foothill forests cover a wide range of environmental conditions. How do you manage for fire in such situations? (Photo by Steve Leonard)

A typical scene in the foothill forests of Victoria. In the morning mist this patch of woodland doesn’t look particularly fire prone but the blackened trunks, open canopy and epicormics buds (leaves sprouting from the main tree stem) suggest a major fire has passed through here recently. Indeed, this image was captured some 15 months after large wildfires seared parts of central Victoria. The foothill forests cover a wide range of environmental conditions. How do you manage for fire in such situations? (Photo by Steve Leonard)


KEY MESSAGES:
  • Important insights can be gained by modeling how fire regimes, not just fire events, influence biota in forests
  • Management of fire regimes needs to be complemented by an understanding of the underlying environmental gradients and key elements of habitat structure that influence resource availability for plants and animals

The flame robin (Petroica phoenicea) is an insectivore that feeds from open ground. Statistical analysis showed that it was one of few vertebrate species more likely to occur in recently burnt vegetation. (Photo by Rohan Clarke)

The flame robin (Petroica phoenicea) is an insectivore that feeds from open ground. Statistical analysis showed that it was one of few vertebrate species more likely to occur in recently burnt vegetation. (Photo by Rohan Clarke)

‘Foothill forests’ cover approximately 7.5 million ha in the state of Victoria (see Figure 1). They are a priority for fire management, containing significant biodiversity and posing risks of fires to people and property. But how do you manage a major natural disturbance like fire when they are occur across a broad-scale environmental gradient like foothill forests?

Foothill forests in Victoria encompass broad-scale gradients of temperature, rainfall, and vegetation type. Along these gradients, fires create mosaics of vegetation with different disturbance histories relating to the time between fires, fire type and spatial pattern in the landscape.

In a new study published in the journal Ecosphere, we brought together data from six major studies (bringing together more than 600 biodiversity survey sites) to provide a more complete picture of the links between biodiversity, fire regimes and environmental gradients in foothill forests (Kelly et al, 2017).

We aimed to advance fire ecology by quantifying species responses to recurrent fires, by modeling species responses to a greater range of fire regimes and environmental gradients, and by comparing species–environment relationships between multiple taxonomic groups in one ecosystem.

Figure 1: Extent of foothill forest vegetation in Victoria and (right) fire history of foothill forest. (From Kelly et al, 2017)

Figure 1: Extent of foothill forest vegetation in Victoria and (right) fire history of foothill forest. (From Kelly et al, 2017)

Species distribution modelling of 32 bird species (493 sites), three small mammal species (175 sites) and 77 vascular plant species (615 sites) showed that common to animals and plants was a strong influence of broad temperature and rainfall gradients. For example, a suite of species was closely associated with high rainfall (eg, silver wattle, Tasman flax lily, yellow-faced honeyeater), whereas others were associated with low rainfall (eg, small grass tree, white-eared honeyeater).

Fire interacted with these environmental gradients and shaped species distributions. We built on previous work by showing that interactions between fire, climate and vegetation type influence the distributions of plants and animals: species can have different responses to fire along broad rainfall and temperature gradients (eg, narrow-leaved wattle and Australian king parrot).

Most fire ecology studies model the effects of fire on plants and animals by using time since the most recent fire. Our results underscore the important insights that can be gained by modelling how fire regimes, not just fire events, influence biota in forests. Inter-fire interval (ie, the average number of years between successive fires at each site) was the most influential component of the fire regime on both plants and animals. For example, the occurrence of vascular plants such as messmate and prickly currant bush was associated with longer inter-fire intervals, in addition to gradients in local vegetation types.

Multiple characteristics of fire regimes influenced the distribution of forest species. Time since fire also influenced vertebrates, particularly bird abundance, more than plants. Of species that responded to time since fire, most were associated with older fire ages (eg, rose robin, golden whistler, yellow-faced honeyeater). The insectivorous flame robin was one of few vertebrate species that was most likely to occur in recently burnt vegetation.

As predicted, animals closely associated with direct measures of habitat structure, such as tree diameter and leaf litter, were those most strongly influenced by fire regimes. Species distribution models including habitat structure had a moderately higher model fit and predictive ability than those using fire regime variables. For example, the flame robin was more likely to occur in open areas. It is likely that resources that are available in the more open understorey of recently burnt forests drive this species’ relationship with time since fire.

Foothill forests are dominated by trees that rapidly recover from wildfires and, on the whole, our results show that common plant and animal species in foothill forests are likely to be tolerant of wide variation in fire regimes. However, although many plants and animals in these forests are resilient to variation in current fire regimes, the potential for large wildfires at shorter intervals, associated with a warmer and more extreme climate, warrants attention from both scientists and land managers.

Managing fire for biodiversity conservation is becoming increasingly important in forests worldwide. Our work in the foothill forest ecosystem in southeastern Australia usefully illustrates several points applicable to other forest areas with high biodiversity, flammable vegetation, and that are experiencing growing use of prescribed burning.

First, our study shows that understanding fire regimes, not just fire events, is important for managing plants and animals in forests. We recommend that forest managers go beyond simple measures of fire events and develop strategic objectives for plants and animals based on fire regimes.

Second, fire regimes in forests need to be understood and managed in the context of environmental gradients, even within a single forest type. Variation along environmental gradients is linked to biodiversity and influences management options and the effectiveness of fire suppression and prescribed burning.

Finally, it is necessary to complement management of fire regimes with understanding of the key elements of habitat structure that influence resource availability for plants and animals. Species relationships with fire regimes may be easier to translate into management plans, but this approach risks missing key habitat components on which taxa depend.


More info: Luke Kelly ltkelly@unimelb.edu.au

Reference

Kelly LT, A Haslem, GJ Holland, S Leonard, J MacHunter, M Bassett, AF Bennett, MJ Bruce, EK Chia, FJ Christie, MF Clarke, J Di Stefano, R Loyn, MA McCarthy, A Pung, N Robinson, H Sitters, M Swan & A York (2017). Fire regimes and environmental gradients shape vertebrate and plant distributions in temperate eucalypt forests. Ecosphere. 8: e01781 http://onlinelibrary.wiley.com/doi/10.1002/ecs2.1781/abstract

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