The gradient rule (substrate writes the country)

The gradient rule is the book's central organising claim, and it is scale-independent. On the Sunshine Coast the reef-to-range transect (the Maleny–Mooloolaba descent) crosses, in order, rainforest on basalt-derived red clay → tall eucalypt forest on mixed sedimentary/loam → floodplain and paperbark swamp on alluvium → wallum heath on leached sand → estuary on tidal mud. Rainfall barely changes across most of that sequence; what changes is the substrate — soil depth, nutrient status (above all the N–P asymmetry), and where water sits or drains. Three rocks, three destinies: rich basalt grows rainforest, hungry sand grows heath, middling sedimentary ground grows open eucalypt forest.

The same rule runs at every scale beneath the whole-coast transect: on one hill (Mt Ninderry — dry, fast-draining exposed slopes grow open eucalypt forest while deeper, damper gullies grow wet forest toward rainforest), across one dune field (Cooloola — tall forest on middle-aged sand giving way to low heath on the oldest, most phosphorus-depleted dunes), even across the two banks of a single creek where one is basalt and the other sand. Reading the country means running this rule backwards: from the living thing you can see to the ground truth that explains it — and reading the exceptions (a lone relict forest red gum marooned in a cane paddock is history, not present conditions: the ground would still grow forest; people changed it).