Impacts on terrestrial and aquatic biodiversity in the North East.
More than half the catchment area in the North East is public land (55%), with extensive areas of national park and State forests. The landscape and vegetation communities are relatively diverse and therefore more inherently resilient to climate change. The cooler climate of the Victorian Alps has been identified as a key climate refuge for the Australian continent. Climate refuges provide cooler, moister or more stable conditions to which species can retreat during extreme events such as droughts, heatwaves or fires and are critical to the survival of species and regional biodiversity
Although the landscape and vegetation communities are relatively diverse and therefore more resilient, the risk to biodiversity in the North East is not uniform, and many species and communities are particularly vulnerable to rising temperatures and changes to fire regimes. The biodiversity values in the North East are currently affected by land clearing, fragmentation of native vegetation, agricultural intensification, and competition from pest plants and animals. Climate change amplifies the impact of these existing threats.
Warmer and drier conditions can impact on species and ecological communities unable to adapt fast enough to the rate of climate change. Characteristics associated with increased climate vulnerability of communities and species include being in poor condition due to existing stresses, having highly restricted distribution or climatic tolerance, small population sizes (often associated with low genetic variability and capacity to adapt), low reproductive output, poor dispersal capacity, and reliance on continuous habitat for migration and dispersal. Species reliant on patches of native vegetation that are small and isolated are particularly at risk where surrounding land uses present a barrier to migration to more suitable climates. Possible impacts from climate change include changes in the dominant species and structure of existing vegetation types, decline or loss of local populations of species, and species extinctions.
In the North East, a south easterly shift in suitable climates will push species towards the Alps and into higher elevations. Mountainous regions will act as a refuge for nearby lowland species, but will not act as refuge for the species that currently rely on cool upland habitat. Alpine environments are extremely vulnerable to climate change as these areas are already confined to the highest of the Australian Alps and climate models predict a decline in maximum snow depth and duration of snow cover. Warming of alpine environments has the counter-intuitive effect of increasing cold-exposure for species such as the Mountain Pygmy Possum, which rely on a blanket of snow cover for warmth during hibernation.
Climate variables affecting water resource quantity and quality (such as declining rainfall and stream flow, and increasing temperature) can also impact on the health of aquatic ecosystems. Drought, erosion of fire-affected catchments, and conditions that favour exotic over native species are the main drivers of decline in aquatic biodiversity associated with climate change. The adverse effects of drought and declining rainfall on aquatic systems can exacerbate historical impacts of changes to streams and catchments, including water extraction, river regulation, and land use change. Along with in stream habitat loss due to sand-slugs, de-snagging, and competition from introduced species, these remain the main causes of aquatic biodiversity decline.
The impacts of further reductions in stream flows and wetland drying are likely to be a change in abundance, decline, or possible extinction of aquatic and wetland species. Cold-water species are expected to be more vulnerable to warming water temperatures than other species. The impacts are likely to be more pronounced in shallow waters and where riparian vegetation has been cleared. The combination of warmer temperatures and resulting changes in aquatic community composition is likely to increase opportunities for introduced aquatic species. Aquatic communities which are in poor condition are likely to be least resilient to changing conditions.
Wetland-dependent species are considered to be more vulnerable to climate change impacts than terrestrial species because of a relatively more severe decline in suitable habitat caused by wetland drying. Seasonal river-fed wetlands, the most common wetland type in the North East, are particularly sensitive to changes in flow regime. Recent studies and investigations suggest that wetland inundation will become much less frequent under moderate climate emissions scenarios. The effects of wetland drying combined with changes to the potential ranges of invasive species will make wetlands susceptible to invasion by non-wetland species, both exotic and native, and possibly see the emergence of ‘sleeper’ invasive species already present within the region.
Research into which ecological communities and local factors are most vulnerable to climate change
Assist species migration and colonisation across known barriers
Contingency planning for threatened communities / species of national signiﬁcance
New environmental plantings with adaptive potential
Maintaining roadside vegetation condition
Identify invasive species advantaged by climate change
Focus governance efforts on large-scale ecological processes and functions