Forest Giants: Locating Southwest Australian Old-Growth Country

Chapter 3 Forest Giants: Locating Southwest Australian Old-Growth Country

John C. Ryan

The wide-ranging context provided by Chapters 1 and 2 situates Forest Family: Australian Culture, Art, and Trees. The old-growth eucalypts of the Southwest of Western Australia are non-human protagonists in the narrative of the Giblett family (Chapters 4 and 5) and the seminal forest protection cam- paigns of the 1990s (Chapter 8) that swept the region and resulted in models for subsequent environmental activism in Australia. Central to this narrative are karri (Eucalyptus diversicolor) and its companion species jarrah (E. mar- ginata). Karris cover roughly 200,000 hectares, or 500,000 acres, about one- fifth of which is classified as old-growth. The iconic forests and charismatic trees are limited principally to a high-rainfall coastal strip extending from the towns of Nannup in the north, Augusta in the south-west, and Denmark in the south-east. The town of Manjimup, where the Gibletts settled, is set within a transi- tional zone between karri forests to the south and jarrah principally to the north. In comparison, the town of Northcliffe (featured in Chapter 7)—which is fifty-five kilometers, or thirty-four miles, south of Manjimup—is ensconced squarely within E. diversicolor territory (see Figure 3.1). The karri belt varies from sixteen to twenty-five kilometers in width but faithfully parallels the Indian Ocean between Albany and Cape Leeuwin. Isolated communities, how- ever, do exist at Mount Many Peaks and the Porongorup Range (Boland et al. 2006, 286). The soils of the old-growth corridor are typically acidic and—to the dismay of colonial-era pastoralists who intuitively correlated large trees to fertile landscapes—deficient in nutrients and trace elements such as zinc, copper, and cobalt (Boland et al. 2006, 286). Karri usually mixes with marri (Corymbia calophylla) and, less frequently, with jarrah, red tingle (E. jacksonii), and yellow tingle (E. guilfoylei). Common understory species include sheoak (Allocasuarina decussata) and karri wattle (Acacia pentadenia). What’s more, the characteristic growth habit of karri has physiological provenance. The efficient “hydraulic architecture” of cells, trans- porting water between roots and leaves, enable trees to grow conspicuously tall and straight, unlike the jarrah, marri, tingle, and fellow eucalypt species

Nannup Augusta Albany

Figure 3.1 Map of Karri Country (grey) located approximately between the Towns of Albany, Nannup, and Augusta, Western Australia in the Southwest Botanical Province (red) (2013). © Modified Version of Original Image from Public Domain via Wikimedia Commons.

(McGhee 2014). Alongside the mountain ash (Eucalyptus regnans) of Tasmania and Victoria, the karri ranks as the tallest angiosperm, or flowering plant, in the world (Griffiths 2001, 17). The largest tree in Australia, in fact, is a mountain ash in Tasmania with a diameter at breast level of more than five meters and stem volume of three-hundred-and-thirty meters cubed (Beadle, Duff, and Richardson 2009, 339). Also known as the Karri Forest Region and the Jarrah-Karri Forest and Shrublands Ecoregion, the Warren is one of eighty-nine bioregions recog- nized under the Interim Biogeographic Regionalization for Australia (IBRA). Demarcated by the Indian Ocean to the south-west and the Jarrah Forest Bioregion to the north-east, the region has a moderate Mediterranean climate with the highest rainfalls in Western Australia. The Warren, moreover, is re- garded as the most important center of endemism for high-rainfall flora in the state (Wardell-Johnson and Horwitz 1996).