How are Australian alpine ecosystems responding to climate change? Measuring shrubs as bioindicators of change, Victorian Alps, Australia.

Background: Climate change poses a clear and present danger to the world, and much recent attention has focused on the ecological impacts in Australia. In many Australian regions, a shift in climate will displace optimal habitats latitudinally or altitudinally. For example, across Australian alpine areas recent climate models suggest higher mean temperatures, more frequent fire and reduced precipitation including less snowfalls. Consequently, alpine ecosystems are responding and therefore opportunities can be gained in measuring bioindicators of climate change. In the Australian Alps, ecosystem responses can be mapped to indicate vegetation patterns that are driven by climate. For example, the widescale expansion of woody plants (which do not normally grow in cold climates), has become an important topic of investigation because woody plants are dispersing into high alpine environments, which have remained treeless for centuries. Woody plants require warmth to produce woody tissue, so, as the atmosphere warms-up, highland areas are becoming more suitable for growth. Thus, by understanding how woody plants express change, the resultant ecological impacts can be evaluated.
Objectives: In this project, alpine woody plant responses are measured using shrubs (small woody tissued plants) and represent climate change bioindicators. I aim to understand if shrubs are embracing new, warmer, opportunities that climate change may be providing across the Bogong High Plains, Victoria. Two related studies will evaluate shrub encroachment patterns across two climate change affected ecosystems where shrubs have remained absent until recently. The two microclimate regions investigated are: 1) Frost basins, where landscape topography facilitates cold air accumulation and impacts shrub thermal tolerance; and 2) snowpatches, where snow cover lasts longer, and shortens the growing season for shrubs. Both these ecosystems naturally challenge shrubs, however, with the current effects of climate change, these ecosystems are likely becoming less limiting and more suitable for their growth and expansion.
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Methods: In frost basins, frost gradients are measured, and correlated with patterns of shrub expansion using various fieldwork sites and statistical approaches. Changes in shrub cover from 1951-2015 are also quantified using Geographic Information Systems and time-series imagery analysis to determine responses over time from weakening frost events. In snowpatches, snowmelt gradients are correlated with patterns of encroachment and shrub change identified over the last 20 years.
Results: Frost basins are expressing many signals of increased per cent cover of shrubs. Encroachment fronts are also expanding downslope into colder areas. However, across frost basins that were burnt since 2003, the influence of fire confounds the measurable effect of frost on plants. But in snowpatches, melting is becoming earlier, and shrubs are invading from the margins through time.
Conclusions: Woody shrubs act as bioindicators of environmental change across the Bogong High Plains. Additionally, it’s reasonable to predict that more widespread and denser growth of woody vegetation will be encouraged as frost events and snowfalls reduce in alpine areas. As encroachment progresses, the predicament worsens as grasslands shrink and the vegetation balance leans toward highly competitive and more flammable woody vegetation.