Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.
Sunday, 8 May 2011
Sleeper weeds in the alps
Alpine grasslands on the Snowy Range are typically weed-free (Photo: John Morgan)
The Australian Alps were once thought rather resistant to weed invasion because the cold climate would act as a strong selection against many non-native species. It is certainly true that mountain grasslands and herbfields are much less invaded than their lowland counterparts. In the lowland grasslands of south-eastern Australia, a suite of Eurasian grasses that evolved in human-dominated ecosystems have been particularly successful at invading native ecosystems. These grasses have been far less successful at higher altitudes where there has been no agriculture.
Recent studies confirm, however, that many weeds do occupy the treeless mountains in Australia. McDougall et al. 2005 found over 125 species had become naturalised in alpine vegetation and it is highly likely that many species currently found at lower altitudes could become future invaders (Alexander et al. 2011).
It is within this context that managers of alpine vegetation need to make decisions about what weeds to control, where and why. Some emerging weeds (such as Hawkweeds and Willows), as well as some species well-established in alpine areas (Broom), are currently the target of annual, resource-limited control programs in NSW and Victoria. But what about future invaders? Who might they be? Where might they invade? And which ones should be controlled?
Recently, I undertook some monitoring in the Victorian Alps with the specific aim of recording locations of new weed incursions. I have been undertaking weed surveys in remote alpine areas for over a decade now - typically, I visit areas that are free of serious invasions and walk ad-hoc transects over several days that cover a variety of aspects, vegetation types and altitudes. These long-term observations hint that some species currently not considered serious invaders are 'on the move'.
One such plant is Ox-eye Daisy (Leucanthemum vulgare). From the daisy family, this species has always had a presence in subalpine woodland near Dinner Plain, but it was scattered and apparently not very competitive. In 2011, however, it now appears to have dramatically increased both its range and its abundance - hence, it constitutes an example of a 'sleeper weed' - a species that has been in the area for a long time at low density before rapid population growth.
Large areas of subalpine grassland and woodland near Mt Hotham are covered in Ox-eye, and satellite populations are spotting all over the place. This seems to be occurring in the absence of soil or vegetation disturbance. Worryingly, the same is happening on the snowplains near Kiandra in Kosciuszko National Park. Whether Ox-eye has negative impacts on native plant biodiversity awaits further study, but it highlights that alpine areas are likey to come under increasing pressure from invaders, particularly as climates warm.
Alpine summits currently support few invasive species - but for how long? (Photo: John Morgan)
Early detection of exotic species would appear to be one of the best defences we have against their invasion and subsequent dominance - hence, on-going monitoring of alpine vegetation would seem a good investment to me and the challenge will be to develop monitoring strategies to detect these intially rare (but potentially important) incursions.