James Cook University, Townsville

Leonie Valentine

Aims | Introduction | Fire as a tool to manage rubber vine | Study sites | Methodology | Preliminary results | Summary | References |

Fire treatment site, Burdekin Catchment, Cornishman Creek, Queensland

Project Aims

This study uses an experimental approach to investigate how native animals, particularly birds and reptiles, respond to the presence of one of northern Australia's most pervasive weeds, rubber vine ( Cryptostegia grandiflora ). As fire is now being used to manage rubber vine, the study is also examining how these animals respond to fire.

Specifically, this project will answer five questions:

• Is the richness or structure of bird and reptile assemblages affected by the presence of rubber vine, and how do particular species of birds and reptiles respond to rubber vine infestations?

• What are the short and medium term impacts of different seasonal controlled burning on bird and reptile assemblages?

• What are the short-term impacts of a repeated control burn on bird assemblages?

• Do predation rates of birds on skinks increase following controlled burning?

• What are the impacts of mosaic burning on bird assemblages?

Preliminary results indicate the burning strategies to control rubber vine are affecting some faunal species and assemblages. Although the majority of species affected had higher abundances in the burnt treatments, at least one fire-sensitive species, the Red-backed Fairy Wren, was identified.

Introduction

Plants introduced to Australia that become weeds can have devastating consequences on both native animals and plants.

Large areas of Queensland's pastoral land have been invaded by rubber vine since its introduction into Australia in the late 1800s from Madagascar (Grice 1997). The vine has spread rapidly along riverbanks and adjacent open woodlands in northern Queensland, causing problems for graziers and potentially reducing the native biodiversity values of the state's open woodlands (Bebawi and Campbell 2002).

The weed's invasive nature and tendency to smother trees and shrubs has reduced the biodiversity values of native vegetation, but the impact of rubber vine on native animals is unknown.

Fire as a tool to manage rubber vine

In Australia, fire is often used as a contemporary management tool to control introduced weeds, including rubber vine. Research indicates that fire can significantly reduce rubber vine and has the potential for widespread use in tropical savannas of northern Queensland where riparian systems are infested (Grice 1997). However, the impacts of such fire management on native fauna are largely unknown.

Fire and fauna studies, primarily conducted in the Northern Territory, suggest that faunal assemblages are strongly influenced by fire and, particularly in the tropics, by the components of a fire regime (Braithwaite 1987; Woinarski et al . 1999).

The differences in habitat, community structure and land use between Queensland and the Northern Territory are likely to produce different responses to fire among faunal communities.

The striated pardalote ( Pardalotus striatus ) was one of a number of birds that Leonie found in higher abundance in dry burnt treatments compared to unburnt treatments.

Reptile species diversity, abundance and composition were similar across all treatments. Above is the knobtail gecko, Nephrurus asper

Study sites

The effectiveness of different fire regimes for controlling rubber vine was investigated by CSIRO Sustainable Ecosystems (CSIRO SE) in a Tropical Savannas CRC-funded project (see web link below).

Through this research, a protocol to investigate fire as a management tool was developed for controlling rubber vine in grazed riparian environments of open woodlands.

Replicate experimental study sites, encompassing 2-3 km of creek line and adjacent open woodland were established on three separate tributaries of the Burdekin River on leasehold cattle grazing properties in Dalrymple Shire, north Queensland.

Five plots, separated by double firebreaks, were established at each site, spanning both sides of the creek bed. Each plot comprises about 20 ha and covers both riparian and woodland vegetation. Five fire treatments are being used, including single and successive fire in both the dry and wet seasons and unburnt controls.

The study's design allows the simultaneous examination of the effects of single versus repetitive burning and seasonality of the burns.

These sites also provide an excellent opportunity to examine the impact of fire regimes and exotic species on how native faunal communities are structured in the open woodlands of the Burdekin River Catchment. Results will feed into a comprehensive management strategy for the region.

Methodology

Question 1: Is the richness or structure of bird and reptile assemblages affected by the presence of rubber vine, and how do particular species of birds and reptiles respond to rubber vine infestations?

Rubber vine regularly occurs as shrubby thickets (1-2m high) along riparian systems where it displaces native vegetation thickets. This may potentially affect native birds and reptiles that regularly use vegetation thickets and associated microhabitats, such as leaf litter. This part of the project aims to determine how representative birds and reptiles use rubber vine as habitat. Assemblages of fauna in both rubber vine and native vegetation patches are being compared, along with variables such as the availability of prey, vegetative structure and air temperature.

This particular study site is located along Six Mile Creek, an ephemeral tributary of the Burdekin River in open woodlands where rubber vine is prevalent.

Broad vegetative structural variables, including rubber vine intensity, number of trees and shrubs, will be described, and the characteristics of microhabitats (leaf litter, composition of leaf litter, substrate composition, foliage cover) will be collected for each thicket.

Species composition of birds and reptiles in native vegetation versus rubber vine thickets will be compared, and related to habitat variables and insect biomass.

Question 2: What are the short and medium term impacts of different seasonal controlled burning on bird and reptile assemblages?

Seasonality of a burn can be an important component in determining faunal responses to fire. Potential rubber vine fire-management strategies include burning in both wet and dry seasons. The CSIRO SE experimental fire sites examined fire treatments that included wet, dry and an unburnt control.

The composition of bird and reptile species within each fire treatment will be compared to each other, and to the unburnt control, at two intervals to determine the short-term (5-12 months post-fire) and medium term (2-3 years post-fire) impacts of seasonal burning.

The first sampling period occurred in the wet season of 2001, and the second sampling period occurred in the wet season of 2003.

Differences in microhabitat (percentage leaf litter, grass, rocks, canopy cover, number of trees) will be examined and the effects of structural vegetation changes on fauna will be examined by integrating data from the fauna survey results with that produced by the microhabitat surveys.

Question 3: What are the short-term impacts of a repeated control burn on bird assemblages?

Another potential fire-management strategy is repeated, or successive, burning. The impact of of these fires will also be investigated The short-term impacts of successive fires on bird assemblages will be examined by comparing species composition between a singularly burnt plot, a repeatedly burnt plot, and an unburnt control. Treatments were sampled in the wet season one year following the initial fire, and were again sampled in the wet season one year after the second fire occurred. Species composition of birds and vegetation structure will be surveyed as outlined above.

Question 4: Do predation rates of birds on skinks increase following controlled burning?

One potential ecological consequence of fire, following the removal of ground vegetation, is an increase in birds preying on on skinks (Woinarski 1990) because of greater visibility and accessibility. This will be examined by comparing predation rates in burnt and unburnt plots..

Predation rates will be determined by assessing the frequency of avian attacks on life-like skink models placed in each treatment. Skink models will be made by attaching Blu-tac ^® onto hard plastic bases cut in the shape of a skink, and then spray-painting them to resemble Carlia munda , a commonly occurring skink. Models will be placed in transect lines in each habitat of the treatments at each creek for ten consecutive days.

Question 5: What are the impacts of mosaic burning on bird assemblages in grazed riparian environments of northern Queensland?

Research into the impacts of fire on faunal assemblages indicates a variety of responses to fire with certain fire regimes favouring some species, while disadvantaging others (Braithwaite 1987; Woinarski 1990). This has resulted in an emphasis on conservation managers to implement burning patterns that result in a mosaic of patches across the landscape aimed at maximising biodiversity (Woinarski & Recher 1997).

Surprisingly, however, the efficiency of mosaic burning in enhancing overall diversity has never been demonstrated in the literature. As the study sites represent three replicates of fine-scale mosaic burning, incorporating unburnt, seasonally burnt and repeatedly burnt habitat, along sections of three creeks. This provides a good opportunity to examine the impact of mosaic burning on bird assemblages by comparing the CSIRO-SE study sites to three creeks in the same region that have not undergone mosaic burning patterns.

Bird assemblages will be surveyed in both woodland and riparian habitats along 2 km sections of each creek. Half-hour timed surveys will be conducted at each creek until no new species are detected in three consecutive surveys. Species diversity, abundance and assemblage structure will be compared between variably burnt and control creeks. Vegetation structure at each creek will be described using eight large (20 x 10 m) quadrats in each habitat of each creek. Variables recorded will include number and species of trees, number of shrubs, presence of ground cover, flowers and fruit and canopy cover.

Preliminary results

A fauna sampling strategy was established during the wet season of 2001—as part of my Masters qualifying project—and aimed to determine bird and reptile species richness and abundance. The preliminary results include the short-term impacts of seasonal burning on bird and reptile assemblages.

Differences in faunal assemblages of birds and reptiles were investigated by comparing species number and abundance between replicate fire treatments (unburnt control, wet-season burnt—12 months since fire, dry-season burnt—6 months since fire).

Figure 1: Overall mean bird abundance per fire treatment (* represents treatment different to control).

Figure 2: Mean feeding category abundance of birds per fire treatment (* represents treatments different to control)

The structure of bird assemblages was further investigated by grouping birds into feeding categories based on dietary preferences. Preliminary analysis documented a higher overall abundance of birds in the dry-season burnt treatments, compared to the unburnt controls (Figure 1). Assemblage structure (using feeding categories) of birds also varied between treatments with higher abundances of insectivores observed in both the burnt treatments compared to the unburnt treatments (Figure 2).

Some individual species of birds were found in higher abundances in dry burnt treatments compared to unburnt treatments. These included the Pied Butcherbird ( Cracticus nigrogularis ), Striated Pardalote ( Pardalotus striatus ), and Pale Headed Rosella ( Platycercus adscitus ).

The Red-backed Fairy Wren ( Malurus melanocephalus ) had lower abundances in both the burnt treatments compared to the control indicating a potential sensitivity to burning practices. Reptile species diversity, abundance and composition remained similar across all treatments, although higher abundances of Carlia munda were found in dry burnt treatments compared to unburnt controls.

Seasonality of fire is often considered a biologically important aspect of fire regimes as it largely determines intensity and extent of burn (Braithwaite and Estbergs 1985; Christensen et al. 1981). The dry-season fire may have altered the vegetation structure more dramatically than did the wet season fire, favouring higher abundances of certain species, but not others. Alternatively, differences in bird abundance between burning treatments and controls may be related to time since fire. Previous studies suggest an initial increase in general bird abundance in the first six months post-fire, due to an increase in food abundance or availability (Woinarski and Recher 1997).

Summary

Results indicate the burning strategies to control rubber vine are affecting some bird species and the overall bird assemblage structure. Although the majority of species affected had higher abundances in the burnt treatments, at least one fire-sensitive species was identified. Further study is required to better understand the impact of weed management burning on faunal assemblages in riparian environments of grazed open woodlands in Queensland. The study will also contribute to examining a broader conservation management theory on mosaic burning to maximise species diversity

References

Bebawi, F. F., and S. D. Campbell. 2002. Impact of early and late dry-season fires on plant mortality and seed banks within riparian and subriparian infestations of rubber vine ( Cryptostegia grandiflora ). Australian Journal of Experimental Agriculture 42 :43-48.

Braithwaite, R. W. 1987. Effects of fire regimes on lizards in the wet-dry tropics of Australia. Journal of Tropical Ecology 3 :265-275.

Braithwaite, R. W., and J. A. Estbergs. 1985. Fire patterns and woody vegetation trends in the Alligator Rivers region on northern Australia. Pages 359-364 in J.C.Tothill and J.J.Mott, editors. Ecology and Management of the Worlds Savannas . Australian Academy of Science, Canberra.

Christensen, P., H. Recher, and J. Hoare. 1981. Responses of open forests (dry sclerophyll forests) to fire regimes. Pages 367-393 in A. M. Gill, R. H. Groves, and I. R. Noble, editors. Fire and the Australian Biota . Australian Academy of Science, Canberra.

Grice, A. C. 1997. Post-fire regrowth and survival of the invasive tropical shrubs Cryptostegia grandiflora and Ziziphus mauritiana . Australian Journal of Ecology 22 :49-55.

Woinarski, J. C. Z. 1990. Effects of fire on the bird communities of tropical woodlands and open forests in northern Australia. Australian Journal of Ecology 15 :1-22.

Woinarski, J. C. Z., C. Brock, A. Fisher, D. Milne, and B. Oliver. 1999. Response of birds and reptiles to fire regimes on pastoral land in the Victoria River district, Northern Territory. The Rangeland Journal 21 :24-38.

Woinarski, J.C.Z. & Recher, H.F. (1997) Impact and response: a review of the effects of fire on the Australian avifauna. Pacific Conservation Biology 3 :183-205.