Discussion Paper - Part A - Victorian Environmental Assessment ...

Grazing may also: reduce the capacity for riparian zonevegetation to act as a nutrient ‘filter’; compact soil; andincrease erosion where bare soil has been exposed,therefore increasing sediment input into waterways(Figure 5.27).Alternatively, domestic stock grazing can positivlyaffect the environment if applied in a strategic manner.Grazing cattle and sheep for a limited time in springcan help to reduce weeds by restricting seed set andflowering in certain annual species. Low-level sheepgrazing is applied in grasslands such as Terrick TerrickNational Park to maintain an open habitat preferredby many threatened flora species.The limited studies that have been undertaken todetermine the effectiveness of different grazingstrategies for maintaining and enhancing biodiversitysuggest that intermittent grazing provides the bestbiodiversity outcomes by creating vegetationheterogeneity through both time and space (Dorrough etal. 2004). Continuous and intensive grazing can cause asignificant loss of habitat value through speciesselectivity, changes to vegetation structure and impactson habitat values (e.g. Chesterfield 1986; Jansen &Healey 2003). However, a varied vegetation structure canhave less useable forage and therefore has not generallybeen favoured by graziers (Dorrough et al. 2004). Thismismatch in land management objectives is one of themain impediments to the introduction of strategicgrazing management with biodiversity conservation as aprimary objective across parts of the public land estate.Changes due to intensive grazing may be irreversible inthe short to medium term, and a significant allocation ofresources may be required to restore native vegetation.In particular, damage to stream frontages is significant.A site’s ability to recover from grazing damage dependson stocking density, soil type, geomorphology andtopography and is therefore highly variable (Robertson &Rowling 2000; Martin et al. 2006). There may be asubstantial time lag between the time of revegetationand the re-establishment of animal populations (Vesk &Mac Nally 2006)In addition to domestic stock grazing on public landwithin the study area, there are native grazers(kangaroos and wallabies) and feral grazers (feral cattle,rabbits, hares, fallow deer, feral horses/brumbies, goatsand pigs). When in large populations, these additionalgrazers contribute to over-grazing of vegetation. Thehard-hoofed feral cattle, brumbies and goats alsocontribute to trampling, soil compaction and erosion.Climate Change, Greenhouse and BiolinksClimate change, both natural and due to increased levelsof greenhouse gases in the atmosphere, is described inchapter 4. This section looks specifically at the potentialeffects of climate change on biodiversity. Climate changerepresents a major new threat to biodiversity andecosystem services for the 21st century with somepredicting mass extinctions (Thomas et al. 2004).Climate change is predicted to change the distribution,configuration and abundance of species and ecosystemservices.The types of species most at risk from greenhouseeffects have been divided into six categories (Mansergh& Bennett 1989; Brereton et al. 1995):• Genetically impoverished and/or localised populations• Poor dispersers and annual plants• Specialised species, especially those dependent onmature vegetation, e.g. superb parrot• Peripheral or disjunct populations• Coastal species• Montane and alpine speciesThe implications of climate change on the flora andfauna of river red gum ecosystems require furtherstudies, especially for invertebrates. In theory, globalwarming could affect invertebrates by increasing thedevelopmental rate of species, thus resulting in moregenerations each year for some species. This could occurboth for herbivorous insects and for their naturalenemies. Another possibility is that insects from coolerregions of the river red gum range could be displaced byspecies better adapted to warmer temperatures. Thiscould promote invasive invertebrate species currentlyonly found further north. The knowledge base regardingthe invertebrate fauna on river red gums is inadequateto allow further speculation.Modelled responses of fauna to climate change insoutheastern Australia has lead to the identification ofclimatic refugia (areas where species will experience aclimate similar to the present) and a series of biolinkzones in Victoria (Bennett et al. 1992; Brereton et al.1995), which have since been recognised in governmentpolicy (DCE 1992b). Biolink zones are areas that willmaximise the capacity for species to “move”, recoloniseand reconfigure as they adapt to climate change (seeMansergh et al. 2005). The Murray River and associatedriparian vegetation and wetlands have been identified asa key sub-continental scale “biolink”.A National Action Plan (NAP) has been developed forAustralian biodiversity in response to greenhouse climatechange (NRMMC 2004). In strategy action 5.1 (p. 27)the NAP seeks to implement “strategies to reduce thephysical barriers to movement to facilitate the migrationand dispersal of terrestrial species and communities thatare vulnerable to climate change”. The River Red GumForests study area has been identified as a major link,provided by its contiguity in linking different habitatzones (DCE 1992b; Brereton et al. 1995). However,vegetation conditions could be improved to maximisethe river red gum’s value as a biolink (ARIER et al. 2004).Further, recommended actions of the NAP include to“identify and implement opportunities to re-establishnative vegetation and enhance habitat for vulnerablespecies on private land through revegetation, vegetationmanagement and land-use change program”. Thevarying width of native vegetation (in both NSW andVictoria) along the rivers provide opportunities toimprove the area as a biolink.FireFire (see chapter 4) is vital for many Australianecosystems and shapes the composition and distributionof plant and animal communities across Victoria. Plantshave adapted to fire over millions of years and havevarious survival mechanisms. Some trees with thick barkmay lose their canopy but survive the fire and grow newDiscussion Paper85