Across southern Australia, livestock grazing has been so widespread and intense that it's transformed the natural grassy ecosystems, sometimes beyond recognition. Early settlers were drawn to the vast grassy plains of the lowlands, as well as the drought relief that the alpine high plains provided. For ecosystems that evolved in the absence of large, hooved, congregating animals, it's no wonder that changes in the native vegetation were recorded within five or so years of occupation by europeans. In many cases, we can only dream of what the original ecosystems might have looked like. Early paintings provide some insights, particularly about the structure of the vegetation and perhaps some of the dominant tree species. For example, the image below shows that the Yanakie Isthmus at Wilsons Promontory in the 1870s was undoubtedly a grassy woodland at the time of settlement, and extensive at that. Today, the Isthmus is covered in shrubs and hardly a blade of grass can be found, a consequence of 100 yrs of stock grazing and fire exclusion.
|From Lookout Hill, towards Mt Latrobe.The trees here are probably She Oaks (Allocasuarina verticillata).|
Painted by John Black Henderson, about 1870. (Image provided by Jim Whelan)
Fenceline comparisons, however, provide much more detailed information about the effects of historical and current regimes on the composition of native vegetation. In some cases, the fences went up in the very early days of settlement (around cemeteries, along railway lines, and to demarcate travelling stock routes), preventing the ecological transformation that occurred throughout the remainder of the landscape that was to be grazed. It's no wonder they have been used extensively in ecology as "natural experiments".
To illustrate the importance of fenceline comparisons, I've been just looking at the distribution of C4 grasses on the riverine plains of northern Victoria with a view to thinking about how to restore and manage these endangered ecosystems. Currently, grasslands here are dominated by C3 grasses such as Wallaby Grass and Spear Grass, with a wide variety of annual and perennial intertussock herbs. C4 grasses are very rare (despite their implied importance in the pre-european flora). The current structural and compositional values are being managed by status quo management - using sheep grazing - based on the idea that the vegetation we see today is a product of its recent grazing history and hence, this is the best way to manage it to maintain those values. But what elements might be negatively affected by such a regime?