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.

Monday, 8 December 2014

Weeds are relentlessly marching into the Australian Alps!

This is the conclusion I have to draw based on lots of new evidence we have been accumulating these last two summers. Alpine areas are currently amongst the least invaded ecosystems in Australia and this has generally been thought to be because the environment is too harsh for many introduced species to survive, hence limiting their establishment. I'm coming to the conclusion that the current low number of species is more a reflection of the fact that many exotic species have yet to arrive there.

MIREN features 11 core mountain regions that
 participate in standardized baseline screening and monitoring.
Our research has shown that the flora and fauna of the Australian Alps is rapidly changing. My Lab is part of the Mountain Invasion Research Network (MIREN), an international collaborative effort to document patterns and processes of invasion into mountain ecosystems. Using standardised survey protocols (mostly using quadrats placed from lowlands to mountain tops), we have now shown that many species have made the jump from the lowlands to the alpine regions. In some cases, this has occurred because they have been deliberately introduced into ski resorts. The introduction and spread of Orange Hawkweed is a good example of this.

Many new arrivals, however, have moved into the mountains by using roadsides as corridors for dispersal. Some, such as Chilean Needle Grass, have never been seen before in the alps until their detection on roadsides near Falls Creek in 2013. Others, such as Sweet Vernal Grass and St John’s Wort, are rapidly expanding their range, using roadsides and walking trails as initial points of introduction into native vegetation.

In general, the number of weeds on roadsides does decline as you move up mountains. You can see  this pattern here - a summary of all plots sampled in the Victorian Alps in 2013.

But don't be fooled. My collaborator Keith McDougall, working in the Kosciuszko National Park, found 25 new species on roadsides when he sampled the same plots five years apart, hinting that the ongoing propagule pressure from vectors such as cars, combined with changes in regional climate, is transforming mountain road verges at incredible rates. Sure, many of these species have not yet moved into the adjoining native vegetation. But it just may be a matter of time.

This figure, using MIREN data from the Victorian transects, shows how far some weeds have moved off roadsides. It's not an insubstantial encroachment of exotic species.


It's not all bad news though.

Red-led Grass is a native grass found on roadsides leading into
high mountain ecosystems. All of its 'natural' distribution
in Victoria is low elevation plains grassland and woodland.

Some native species also seem to be using roadsides to hitch a ride up mountains. Red-leg Grass (Bothriochloa macra), a native C4 grass of the surrounding lowland plains, for example, has been recorded at several mountain roadside sites well above any known location in state databases (i.e., growing up to 800 m above known populations). Is this a 'new' weed, albeit native? It certainly looks like its dispersal is linked to vehicles but it is also likely that recent changes in low temperatures (and perhaps precipitation) play a role.

The movement of natives up mountains is interesting and entirely inevitable; after all, our basic understanding of climate change impacts is that species will migrate pole-wards and up mountains. This example, however, showcases how humans are likely to have facilitated the process and how (mostly) it'll go on undetected.  And, in the bigger scheme of things, it illustrates that native ecosystems will re-assemble in the coming century whether we like it or not.

Further reading about MIREN and mountain invasions:

Kueffer et al. (2014) The Mountain Invasion Research Network (MIREN) - linking local and global scales for addressing an ecological consequence of global change. GAIA 23/3: 263-265.

Pauchard et al. (2009) Ain't no mountain high enough: plant invasions reaching new elevations. Frontiers in Ecology and the Environment 7: 479-486.

This work is supported by funding from the Long-term Ecological Research Network (LTERN) and was conducted by members of the La Trobe University Research Centre for Applied Alpine Ecology.