A picture of one hand holding a plastic bag and another hand holding onto a plant ready to collect some leaves to put into the plastic bag.

Collecting samples of Miconia calvescens at El Arish, North Queensland.

The impact of weeds on rainforests following Cyclone Larry

The project results suggest an ability of invasive plants to persist and compete with native species as the rainforest recovers from the impact caused by Cyclone Larry.

  • 4 May 2009 | Updated 14 October 2011

Background

Severe Category 4 Tropical Cyclone Larry hit the North Queensland coast, Australia, on 20 March 2006 causing extensive destruction to rainforest habitats in the Wet Tropics.

The widespread and massive disturbance caused by the cyclone provided ideal conditions for rapid recruitment and spread of invasive weeds in Queensland’s rainforests. 

Climate change scenarios predict an increasing frequency of intense cyclones in the tropics but little is known about how weeds affect the process of rainforest recovery. 

We have established monitoring sites designed to determine local- and regional-scale impacts of invasive species.

Understanding the dynamics of weed invasion following cyclones and the long-term effects of weeds on forest composition and structure will be critical for implementing management to reduce future impacts. 

Objectives

Monitoring over long time-periods is necessary to provide information to managers about:

  1. what types of invasive species are likely to have significant long-term impacts on rainforests following cyclones
  2. what types of habitat are most at risk from weeds following cyclones
  3. the best approach for pro-active and post-cyclone management of weed species to minimise long-term impacts to rainforests. 

Research activities

We have established monitoring sites designed to determine local- and regional-scale impacts of invasive species. 

The local-scale site was established in April 2006 and consists of 99 (2x2m) quadrats spread over an area of approximately 45 ha in an area severely damaged by the cyclone near El Arish.  

Every seedling, both native and exotic, recruiting in each quadrat has been tagged, identified and its height (or mortality) recorded every 3-4 months since the cyclone. 

At the regional-scale we surveyed 62 (0.1 ha) transects across 36 sites around the Wet Tropics encompassing a range of different levels of cyclone damage, environmental contexts and soil types. 

Over the short term to medium term the results demonstrate competition between native and exotic species and highlight the establishment of some highly threatening weeds in formerly intact native communities.

Miconia calvescens – 'purple plague'

In collaboration with Biosecurity Queensland we are researching how the invasive weed Miconia calvescens responds to the cyclone. 

This pernicious weed is invading the Australian Wet Tropics rainforests and constitutes a major threat to the World Heritage values of the area. 

The species is a serious invader in the tropical Pacific, including the Hawaiian and Tahitian Islands, where it forms extensive monospecific stands and dense thickets that have taken over large tracts of rainforest habitat. 

The spectacular success of Miconia in Tahiti is often attributed to the six hurricanes that hit the Society Islands between December 1982 and April 1983. Reports suggested that the cyclones explained the ‘demographic explosion of Miconia’, and that ‘the speed of the invasion then became astonishing’.

Our results also indicate a rapid response in growth rates of existing Miconia plants to the opening of the canopy caused by the Cyclone as well as a surge in recruitment and low death rates. 

Find out more about Environmental Monitoring & Analysis.