Conservation biology

Green Lab

Lab leader

Peter GreenDr Peter Green

Head of Department, College of Science, Health and Engineering

View profile, publications and contact details

PhD project currently available

Legacy effects of forest harvesting in east Gippsland; has logging in eucalypt forest endangered the survival of warm temperate rainforest?

Warm temperate rainforest exists in east Gippsland as an archipelago of small, linear patches amongst a matrix of mostly flammable eucalyptus forest.  In the past, these patches have probably been protected from the worst effects of wildfire by their topographic position in moist gullies, the inherent lack of flammability of their component species, and the fire retardant effects adjacent wet sclerophyll species. However, it is thought that past logging has significantly altered the last of these factors, permitting highly flammable dry sclerophyll species to re-establish further downslope, and therefore in closer proximity, to rainforest patches.  The consequences of this for warm temperate rainforest are not known, but may include an increased risk of severe crown fire and higher probability of patch loss through conversion to sclerophyll forest types.  There may even be a synergistic effect between past logging and current climate change in endangering the persistence of warm temperate rain forest in east Gippsland.  This project will combine extensive field work conducting vegetation surveys in relation to logging history, with GIS analyses of historical, aerial photographic imagery.  It will suit students interested in forest ecology, rare but significant vegetation types, field work and sophisticated computer modelling.

Interested students please send an expression of interest and CV to either Dr Pete Green or Dr Steve Leonard in the Department of Ecology, Environment and Evolution at La Trobe University by 30 September 2016.  Successful student will be expected to apply for candidature and scholarship through the normal channels (visit by 31 October 2016 (domestic students).

Current conservation research projects

Crazy ant invasion on Christmas Island

The invasion of forest by yellow crazy ants and scale insects is the single largest threat to the biodiversity of Christmas Island. Dr Pete Green and his colleagues have been studying the interactions between red crabs, rainforest, yellow crazy ants and scale insects for many years, and continue to contribute to an ongoing, island-wide program of control and suppression of supercolonies.

Yellow crazy ants (Anoplolepis gracilipes) are probably native to Africa, but now have a pan-tropical distribution. They are highly invasive and have been listed by the IUCN as one of the world's worst 100 invasive species. They have been present on Christmas Island for decades, but only became a problem during the 1990s when they began forming expansive (10s to 100s of ha), multiqueened 'supercolonies'. The density of ants in supercolonies is astonishing, up to 2000 ants per square meter.

Anoplolepis has invaded rainforest on Christmas Island and have built up huge population densities in association with lac scale insects (Tachardina aurantiaca). Supercolonies of yellow crazy ants extirpate local populations of red land crabs, which eat the seeds and seedlings of rainforest trees. In the absence of red crabs, large swathes of rainforest on the island are being transformed.

Supercolonies have transformed the rainforest on Christmas Island. Normally, the feeding activities of the island's famous red land crabs (Gecarcoidea natalis) keep seedling abundance and diversity in check. But at supercolony densities, crazy ants extirpate local crab populations.

Anoplolepis doesn't bite or sting, but subdues its prey with tiny squirts of formic acid. Because there are so many ants, there is sufficient formic acid to kill these large land crabs. The impact of the red crab population has been catastrophic. It is estimated that yellow crazy ants have killed 20 million red crabs – around one third of the entire population – over the last decade.

The deletion of crabs has deregulated seedling recruitment, and led to a transformation of the understory over thousands of hectares.

The image below shows uninvaded forest showing the understory of rainforest with an intact population of red crabs when crazy ants form supercolonies. The ground is clear of litter, and there are few seedlings because red crabs eat most seeds and seedlings:

This next image shows invaded forest showing the understory just a few years after invasion by yellow crazy ants, and the subsequent deletion of the local crab population. Leaf litter persists, and there is abundant seedling recruitment: