Effects of fire on plants and animals: community level
What do we mean by ‘community’?
A community is an assemblage of species populations, which occur together in time and space. A community is usually described in terms of pattern (how species are distributed) and process (interactions between species).
Most management tends to be focused at the community level apart from single-species management which gives special attention to rare or endangered species. At this community level, we are concerned with interactions between species, and changes in species richness and composition, post-fires. As mentioned previously, the most important effects of fires on animals are indirect, caused by changes in availability of food resources, shelter and predation.
Change in community composition occurs because some species are able to survive and thrive following fire, while others are more sensitive and decline. Response to fire can vary depending not only on attributes of taxa of interest, but also characteristics of the fire regime. Sometimes there may be a shift in community composition with the loss of some species and a gain of other species.
Activity: Ant communities & fire
How does fire regime affect ant community composition?
In the tropical savannas of northern Australia, ant community composition was found to differ significantly when comparing annually burnt and unburnt areas.
Describe how the ant fauna of this tropical savanna community differs with fire regime, and why this might be.
Reading:
Andersen, A.N. (1991) Responses of ground-foraging ant communities to three experimental fire regimes in a savanna forest of tropical Australia. Biotropica 23: 575-585.
Further reading
Dyer et al. (2001) will give you a better idea of how different taxa are affected by fires.
Reading:
Dyer, R., Jacklyn, P., Partridge, I., Russell-Smith, J. & Williams, R. (2001) Savanna Burning: understanding and using fire in northern Australia, pp. 40-44. Tropical Savannas CRC, Darwin.
Mechanisms of community change
The mechanisms of community change are generally related to the process of succession.
Previously successional changes in community composition were interpreted in terms of the traditional Clementsian concept of relay floristics. This is where there is a sequence of species replacements following a fire so that one community replaces another in an orderly, predictable process. This results in a climax plant community that is considered biologically stable.
The problem with this is that this classical facilitation process does not often occur, and this theory has proved increasingly inadequate. The main contentious issue is that there can be different community responses depending on fire characteristics and the timing of key life-history events. This makes simple prediction very hard.
Activity: Community & ecosystem dynamics
Have ideas changed?
There have been great changes in the way that ecosystem and community dynamics are viewed by ecologists. These are discussed by Pyne et al. (1996).
Reading:
Pyne, S.J., Andrews, P.L. & Laven, R.D. (1996) Introduction to Wildland Fire, pp. 198-202. Wiley, New York.
Temporal changes in communities appear to be driven more by the relative longevities of species at a site and regeneration traits rather than competitive hierarchies. Thus an understanding of what traits enable plants to survive post-fire is important for understanding community dynamics.
Changes in community composition are now thought to be driven primarily by changes in the interval between fires, with succession following multiple pathways depending on fire history.
Activity: Successional pathways and fire
How do fire regimes affect successional pathways?
This reading discusses southern eucalypt forests and how changes in fire history can alter successional pathways.
Can you draw a flow diagram or conceptual model indicating the different successional pathways? How many potential end points were mentioned in the article?
Reading:
Bond, W.J. & van Wilgen, B.W. (1996) Fire and Plants, p.153. Chapman & Hall, London.
Importantly, while the prevailing fire regime influences plant communities, the reverse is also sometimes the case: plant communities can alter fire regimes. For example flammable plant communities may increasingly gain non-flammable species and in the absence of fire can change to become more fire resistant.
Further reading
In South Africa, Luger and Moll (1992) show that fire suppression has resulted in an expansion of forest patches into surrounding fynbos.
Contrast this with the situation in the tropical savannas of northern Australia where there is not such a clear succession to rainforest. Williams et. al (2003) found that in the absence of fire there appears to be little invasion by rainforest species into savannas.
Can you think why there might be these differences in response and change?
Reading:
Luger, A.D. & Moll, E.J. (1992) Fire protection and afromontane forest expansion in Cape fynbos. Biological Conservation 64: 51-56.
Williams, R.J., Muller, W.J., Wahren, C-H., Setterfield, S.A. & Cusack, J. (2003) Vegetation. In: Fire in Tropical Savannas (A.N. Andersen, G.D. Cook, R.J. Williams, eds.), pp. 105-106. Springer-Verlag, New York.
Gulliver Effect
The balance of grasses and trees in savannas and their interactions are complex, and cannot be understood just in terms of vital attributes or competitive hierarchies. Bond & van Wilgen (1996) coined the expression the ‘Gulliver effect’ which is used to describe a situation where grasses suppress seedlings and slow the growth of adult plants by fuelling frequent fires that kill or stunt the growth of survivors. Grasses are effective at suppressing other plants because of their rapid growth rates. The process results in ‘Gullivers’ which are woody, multi-stemmed shrubs that are stunted and unable to escape this fire trap. Gullivers may persist for many years in this state.
The removal of the herb layer (by grazing or burning), or fire suppression can enable Gullivers to be released from the fire trap.
How do you think this concept might be of use to pastoralists in northern Australia (e.g. in the Victoria River District) who want to increase productivity of their land?
Patchiness & fire mosaics
Patch burning is increasingly being promoted both by researchers for the conservation of specific species in fire-prone habitats, and also by land management agencies who are adopting patch mosaic burning principles into their fire management policies (e.g. Department of Conservation and Land Management (CALM), Queensland Parks & Wildlife Service, Northern Territory Parks and Wildlife). Introducing patchiness and creating fire mosaics is thought to conserve biodiversity and reduce the risk from late season wildfires. Fire patchiness and heterogeneity are assumed to be surrogates for biodiversity, so a patch burning system that aims to promote a diverse fire regime should theoretically maintain biotic diversity. Since different faunal groups and species exhibit a continuum of responses to fires, it is argued that patchy burning will provide a range of seral states and habitats through space and time which will enable the persistence of biota. Patch burning has also been linked with traditional Indigenous burning strategies where traditional burning resulted in a fine-scale mosaic of burnt and unburnt areas.
Although it often appears that there is plentiful evidence to support patch burning, the reality is that no study has explicitly demonstrated that patchiness and mosaics are the best way to conserve biodiversity. Much of the evidence presented is circumstantial, rather than demonstrated. Furthermore, another important issue that needs addressing is how much pyro-diversity is required? What scale should patchiness be created at? Much research is still needed in this area.
Resilience and susceptibility
There can be great variation among communities in their response to fire. Concepts such as resistance and resilience have been used to describe this variation. Resistance is the amount of fire disturbance needed to result in a change (ability to resist change, see Parr et al. 2004) and resilience is the ability to recover from fire. Adaptation and traits that enable fire tolerance will enhance resistance and resilience.
Activity: Community resilience
Is community resilience to fire surprising?
The 1988 fires in Yellowstone National Park, USA, were very large, intense and seemingly destructive. However, plant and animal communities were not as badly affected as first appeared. Researchers now recognise the importance of these stress events, and also the inherent resilience of the communities.
Think about what the main cause of the Yellowstone fires were ascribed to, and give some examples of how the plant community was resilient.
Why did this surprise the researchers?
Reading:
Turner, M.G., Romme, W.H. & Tinker, D.B. (2003) Surprises and lessons from the 1988 Yellowstone fires. Frontiers in Ecology and Environment 1: 351-358.
Some species reduce the potentially negative impact of fires through plasticity in resource requirements (e.g. the ability to change diet and habitat specificity), or reproductive strategies (which can enable rapid population recruitment). There is little direct evidence to support these ideas, and they remain poorly tested at present.
Importantly, in tropical savannas of northern Australia it appears that much of the biota is very resilient and resistant to burning (although there are concerns about the high frequency of late dry season fires occurring in recent times in some areas). Results from the Kapalga fire experiment reveal that overall, many faunal groups are unaffected by fire. Responses are thought to be driven more by other factors, such as rainfall, than by fire disturbance. Furthermore, for many animal species fire occurance is more important than when the fire happens. Fire frequency however may be more important than previously thought.
Activity: Fauna communities & fire
How resilient is savanna fauna to fire?
The range of responses exhibited by fauna in the tropical savannas of Kapalga (pdf document), and their overall high resilience to burning is discussed in this section of the chapter.
Reading:
Andersen, A.N., Cook, G.D. & Williams, R.J. (2003) Synthesis: Fire ecology and adaptive conservation management. In: Fire in Tropical Savannas (A.N. Andersen, G.D. Cook, R.J. Williams, eds.), p.157. Springer-Verlag, New York.
Assessment activity: Fire produces winners & losers in northern Australia
You are required to write an essay. This assessment item will test your ability to communicate findings, develop your skills at researching and critical thinking, and broaden your knowledge of fire effects on biota. For this assessment you will need to use books and journals from the library, and search for relevant literature, as well as the references contained in the Ecology section references (pdf document).
Essay topic: "Fire produces winners and losers in northern Australia ."
Discuss this statement with reference to one taxon in northern Australia (either plants, birds, small mammals, reptiles or invertebrates) and discuss winners and losers for that particular group.
Consider:
- Who are the winners and losers,
- what conditions or fire regimes cause winners and losers,
- and is a winner ever a loser?
In your conclusions, think about what your findings could also mean for biodiversity conservation in northern Australia and what the implications might be for fire managers. Can you make any recommendations for fire managers in northern Australia?
