THE IMPACT OF KUNZEA ENCROACHMENT ON WOODLAND BIRD COMMUNITIES

We usually think of environmental weeds as introduced species.  However, native plants can also become environmental weeds within Australian habitats if, for example, the ecological balance changes due to altered fire and grazing regimes.

Kunzea, a native Australian shrub, has become an environmental weed in some areas of south-east Australia.  It encroaches on native forest and pasture land, forming a dense understorey monoculture and outcompeting other native species.

The impacts of native shrub encroachment on faunal diversity have not been well studied.  The presence of a dense shrub layer is likely to increase the structural complexity and vegetation biomass of open woodland, which could potentially create more bird habitat niches by increasing foraging and nesting opportunities.

Ms Jemima Connell and Dr Michael Clarke from LaTrobe University are investigating the habitat value of Kunzea for bird communities in the Yarra Valley. This project is partially supported by Zoos Victoria, and one of the study sites is the Coranderrk Bushland Reserve (next to Healesville Sanctuary). This research will contribute to the adaptive management strategy for the Coranderrk Bushland Reserve.

AIMS

This project will investigate the following questions:

1. Does the invasion of woodland understorey by Kunzea have an impact on bird communities?
   A. Does bird species richness, abundance and diversity differ between Kunzea-invaded and un-invaded woodland?
   B. Does bird foraging guild composition differ between Kunzea-invaded and un-invaded woodland?
2. Does Kunzea-invaded woodland have fewer, more or different resources to those of un-invaded woodland?
   A. Do Kunzea-invaded and un-invaded woodlands have a similar composition of understorey plant life forms?
   B. Does the vegetation volume and physical structure of Kunzea-invaded woodland differ significantly from un-invaded woodland?
3. How does bird nesting use of the shrub stratum of Kunzea-invaded woodland and un-invaded woodland compare?

METHODS

The researchers are comparing woodlands with a Kunzea-invaded understorey (treatment) to woodlands with an understorey that remains un-invaded (control) at forty study sites in several types of woodland throughout the Yarra Valley.

They have conducted line transect surveys at all sites to identify birds by sight and call. They will then compare bird species richness, abundance and diversity between Kunzea-invaded sites and control sites, as well as the composition of bird communities (in terms of feeding guilds).

The researchers have also conducted nest counts at all sites to assess the breeding value of Kunzea for woodland birds, and are using habitat surveys to sample understorey plant species richness and structural characteristics (e.g. the density of Kunzea and canopy tree species).

Surveys were conducted from late December 2009 to February 2010.

RESULTS

Fieldwork for this project has just finished. Results and conclusions will be uploaded shortly.

FOR MORE INFORMATION

- on the ecology of Kunzea in Coranderrk Bushland Reserve, see:

Singer R, Burgman M. 1999. The regeneration ecology of Kunzea ericoides (A. Rich) J. Thompson at Coranderrk Reserve, Healesville. Australian Journal of Ecology 24:18-24.

- on tours of Coranderrk Bushland Reserve - click here.