Orange hawkweed.

See all stories in this edition
Posted 25 February 2009

Hawkweeds will be affected by climate change, but not necessarily in the way that any one model predicts.

Weed agencies in Victoria and New South Wales have been trying to eradicate infestations of orange hawkweed (Hieracium aurantiacum) and king devil hawkweed (H. piloselloides) in the Australian Alps, urging bushwalkers to report sightings.

Introduced as cottage garden plants, hawkweeds (four species of which have naturalised in Australia) could become one of temperate Australia’s worst weeds.

According to NSW government botanist Keith McDougall, hawkweed “has the frightening potential to change the whole appearance of the Australian Alps, smothering native vegetation and impacting on wildlife reliant on a native understorey”. Orange hawkweed is also a threat to Tasmanian grasslands.

Hawkweeds illustrate the difficulties of predicting the influence of temperature and rainfall changes in combination with the impacts of extreme events.

According to Darren Kriticos and colleagues (2006), hawkweed currently persists in some cooler areas by reproducing only in warmer years. Climate change may see its seed production increase and an expansion of its potential invasive range.

But recent modelling by Linda Beaumont and colleagues (2009) found that climatically suitable habitat for three hawkweed species was likely to contract by 2030, their lower altitudinal limits pushed higher.

On the other hand, because hawkweeds fill gaps created by disturbances, they are likely to benefit from more frequent fires and heatwaves. Their total range may be smaller but their impacts worse.

The work of Dr Beaumont and colleagues highlights some of the difficulties of predicting the range of invasive species, even without factoring in climate change.

When plants invade new territories they often exceed the climatic envelope of their native ranges (by escaping pathogens, herbivores and other constraints, for example).

The researchers found substantial differences among the models they tested using data from the native ranges and “ecological” ranges of hawkweeds. The distributions based on their native range were 47–93 per cent smaller than those based on their combined native and invasive range.

The researchers stressed the importance of using multiple models and factoring in the tendency of some invasive species to occupy different climatic niches in new territories. The ISC supports these recommendations.

Although hawkweeds are banned, according to the Weeds CRC they are sometimes sold by nurseries, and seeds may be a component in wildflower seed mixes.

Find out more
Download the Orange hawkweed fact sheet from Weeds CRC – PDF (324kb).

References
Beaumont, L.J., Gallagher, R.V. et al. (2009) Different climatic envelopes among invasive populations may lead to underestimations of current and future biological invasions. Early View Online in Diversity & Distributions.

Predicting the potential geographic distribution of weeds in 2080. Proceedings of the Fifteenth Australian Weeds Conference Melbourne, Weed Science Society of Victoria.