Weeds - Phase 1 - Research Highlights

Blue Mountains weeds management

Integrating adaptive weed management and biodiversity conservation in the Blue Mountains

What the report is about

Invasive weeds present a serious threat to primary productivity and conservation of biodiversity in Australia. The Australian Government has listed lantana, Lantana camara L. sensu lato, as one of the country's worst weeds. This weed is expanding its range further south and inland, and it is important to understand how it might progress and further compromise Australian landscapes.

The Blue Mountains region was taken as a case study for investigating the potential spread of lantana because Blue Mountains City Council is very interested in maintaining the effectiveness of its weed control operations and better understanding the potential threats new arrivals might pose, and in continuously improving its weed management strategies.

In addition, private landholders are keenly aware of the threats weeds pose to native biodiversity.

Finally, Blue Mountains City Council manages the urban-bushland interface between townships and the Greater Blue Mountains World Heritage Area, so its work is often the first line of defence when protecting the World Heritage values of the surrounding national parks.

Because future climatic conditions are likely to become more suitable for lantana, it is important to begin containing the weed now. The weed modelling work done for this study aims to give managers the information they need in order to identify suitable habitat and potential incursion pathways for lantana westward through the Blue Mountains.

Who is the report targeted at?

The research is relevant to anyone trying to manage new weed infestations (particularly lantana) - including land managers at Blue Mountains City Council, private landholders and, since the study area includes portions of Blue Mountains National Park, the New South Wales National Parks and Wildlife Service. Among the relevant townships are mountain towns from Lapstone in the east and along the Great Western Highway to Mount Victoria in the west.

The recommendations arising from the study are aimed at on-ground land managers, policy makers assessing weed management priorities, local government officials making land-use decisions, and private landholders.

Aims/objectives

This research aimed to develop a habitat suitability model for lantana (Lantana camara L. sensu lato) in a portion of the Greater Blue Mountains World Heritage Area at present and under forecast warmer climates.

A primary objective of the study was to identify which sections of the local government area were most susceptible to lantana invasion since the weed is currently abundant only in the easternmost townships. Additionally, considering that lantana has historically preferred warmer temperatures, the potential for its spread under climate change throughout the Blue Mountains was investigated by simulating temperature increases. A third objective was to compile a list of at-risk vegetation communities and species, using the results from the identification of susceptible areas.

Methods used

Habitat suitability modelling was used to identify at-risk areas. Specifically, a generalised additive modelling approach was used; taking 2001 survey data compiled by Blue Mountains City Council and using them to identify the factors most responsible for lantana's persistence in the region, as well as predicting which areas of the landscape are most suitable for the weed at present and under warmer climate conditions.

The research area consisted of the Blue Mountains City Council local government area, plus a 2‑kilometre buffer around its boundary and a north-east extension into the neighbouring Hawkesbury local government area.

Results/key findings

The habitat suitability modelling work identified temperature as the most important environmental variable currently restricting lantana's presence to the lower altitudes along the eastern reaches of the local government area.

Although only 15 per cent of the study area was found to be suitable for the weed at present, after a 3°C simulated rise in maximum temperatures 58 per cent of the study area was declared suitable. The region's riparian areas were identified as relatively high temperature pathways by which lantana might progress into the Greater Blue Mountains World Heritage Area.

Five endangered ecological communities (as mapped by Blue Mountains City Council) were identified as being at risk of lantana invasion in the near future: Shale-Sandstone Transition Forest, Blue Mountains Shale Cap Forest, Sun Valley Cabbage Gum Forest, Blue Gum Riverine Forest, and Sydney Turpentine Ironbark Forest. At least 27 endangered species (as identified by the relevant legislation) are thought to exist in these communities and are thus under additional threat because of lantana invasion.

The research has directly responded to calls for the integration of weed management with biodiversity conservation. Just as the methods for developing the habitat suitability model can be adapted to other weeds where presence and absence data are available, so can the strategy for integrating biodiversity conservation be adapted. If these techniques are extended to other weed species, an assessment of the collective threat Australia's worst weeds pose for the country's native biodiversity is possible.

Implications for relevant stakeholders

The research led to the identification of important factors determining lantana's spread into the Blue Mountains and thus Australia's alpine areas, with potential new considerations for management of warm-weather weeds in these regions-such as emphasising the potential for ingress via riparian areas. In addition, the work explicitly incorporated biodiversity considerations in weed mapping, allowing for targeted control and a greater appreciation of the threat weeds pose to specific vegetation communities and endangered species.

Recommendations

In view of the changes probably in store for the climate of the Blue Mountains, it is imperative that management make efforts to reduce lantana's population while it still has the help of cool winters and frequent frosts: such assistance might not be available for much longer.

Noxious weeds control teams suggested that the model and up-to-date surveys would draw attention to the urgent need to control lantana now rather than in the future. Allocating control measures to existing infestations at present is likely to be cost-effective given the weed's potential to spread extensively when temperatures become warmer.