The mesic refugium (a wet island in a dry land)

Drive fifteen kilometres east from the Adelaide coast and the country changes under you in a way you can feel through the windscreen. The dry, sun-struck plain gives way to hills, and the hills are green — not the grey-green of saltbush but the deep green of forest, fern and standing water. You have climbed out of the drought and onto a wet island.

The mechanism is rain, and the rain is a gift of height. The Mount Lofty Ranges force the moist westerly air upward, and as it rises it cools and drops its water, so the high hills gather something like a thousand millimetres a year or more where the plains below make do with barely five hundred (Armstrong 2003). Add cooler summits and deep, shaded gullies that the summer sun never fully reaches, and you have a pocket of cool, moist climate — a mesic environment, in the ecologist’s word — sitting improbably in one of the driest corners of the continent.

That island shelters things the plains cannot. Stringybark forest, tree-fern gully, the peaty Fleurieu swamps and the small, secretive birds bound to them persist here as relicts of a wetter past, marooned above the drought like plants left on a mountaintop as the climate warmed beneath them. It is exactly the kind of refuge that makes Mediterranean-climate regions such concentrated stores of life worldwide (Myers 2000) — and the kind now most at risk, cleared to fragments and squeezed by a warming, drying, peri-urban world at its edges (Bardsley 2015). A refuge can also be a cul-de-sac.