Islands in the sky

I live in the Box Ironbark country of Central Victoria. We don’t have any mountains here, just nice rolling landscapes of hill and valley, and occasional plains. We do have some nice hills, that are just high enough to be different to the surrounding plains. The standout is Lanjanuc (Mt Alexander). It rises about 350 metres above the surrounding area, just enough to feel different and sometimes generate its own weather.

It is part of the Harcourt granite intrusion, and feels quite different to the surrounding sand and siltstone country. It was important as a sacred ceremonial ground for the Jaara people. It has a mix of vegetation, but climbs into Manna Gum and Messmate on the higher slopes.

These higher areas that sit in amongst landscapes of lower elevation often contain different species to the surrounding area.

macedoncrossIn our region this is no more apparent then at Mt Macedon, which sits slightly above 1,000 metres above sea level. In winter it is often briefly visited by snowfall, and it can feel moody and cloudy when it is bright and clear on the basalt plains to the south. Known as Geboor or Geburrh in the Woiwurrung language of the Wurundjeri people, the mountain has a rich mix of species that seem out of place in the dry and low lands of Central Victoria.

As you climb from the Kyneton plains you pass through dry Messmate/ gum forest and then into a wet Messmate/gum forest. Then up into Alpine Ash and finally pockets of Snow Gum. Since the Ash Wednesday fires of February 1983, there has been prolific regeneration across the mountain, including stands of wattle across much of the summit ridge, and stands of young Alpine Ash crowd in against the road. The understorey contains plants you would expect to find in the gullies of eastern Victoria, such as Hazel Pomaderris and Austral Mulberry, and Mother Shield and Fishbone ferns.

Mt Macedon2Sheltered gullies with towering Mountain Ash trees and giant ferns can be found within a short distance of the sub-alpine low woodland dominated by Snow Gums on the highest points.

Quite a few plant species that are generally confined to the eastern highlands (the higher hills to the north east of Melbourne) and the Victorian Alps can be found at Mount Macedon at the most western limit of their ranges. Examples of these are the Alpine Ash (Eucalyptus delegatensis) and Mountain Beard-heath (Acrothamnus hookeri).

Other species following a similar distribution are the Sharp Beard-heath (Leucopogon fraseri) and the Mountain Tea-tree (Leptospermum grandifolium), both recently discovered at Mount Macedon.

Mt macedonThe fact that this isolated mountain has species that exist well to the east suggests that there was once a much larger cool temperate forest system that has slowly been forced up to the higher elevations as the climate has warmed. There are similar pockets of snow gums in places like the Cathedral Ranges to the north east of Melbourne.

In scientific terms, this appearance of isolated pockets of vegetation is studied through Island Biogeography. Biogeography is the study of the geographic location of a species. Island biogeography is the study of the species composition and species richness on islands. Island biogeography is aimed at establishing and explaining the factors that affect species diversity of a specific community. An island in this context, is not just a segment of land surrounded by water. It is any area of habitat surrounded by areas unsuitable for the species on the island, such as mountain tops. There are other such pockets in Victoria, like the Buffalo Plateau, which hosts sub alpine woodlands and frost hollows separated from the rest of the Alps by dozens of kilometres.

Mt Macedon1But leaving science aside, what amazes me about these little pockets of isolated vegetation on mountain tops is the slow, beautiful cycles of change that wheel through all landscapes. It stretches my brain as I try to understand the deep periods of time that have passed, as landscapes have slowly warmed and cooled, got drier and wetter, treelines have climbed, and trees have been pushed out to be replaced by grasslands. What amazes me even more is the fact that indigenous people lived through many of these cycles, including the lower sea levels that saw the land bridge connection to Tasmania and when the Yarra River ran way out onto plains that are now covered by Bass strait.

This is the deep time I try to imagine as I sit on the crest of Macedon’s summit ridge, looking out to the south west, feeling those young snow gums pushing at my back, hanging on for dear life in a time of climate change.


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