Soils in the Wet Tropics are predominantly derived from granites and rhyolites, and metamorphic sedimentary rocks. They vary from thin, stony, leached and infertile ‘lithosols’ of some ridge-tops to the deep, red, rich and fertile basalt derived soils of the Atherton Tableland and the alluvial soils of the coastal lowland plains which can be over 60 metres deep.
The soils derive from a wide range of parent rocks, alluvia and rainfall gradients. The parent materials consist of acid igneous rocks, low-grade metamorphics, basalt, and alluvium derived from these. The alluvium of larger streams is of mixed origin; that of smaller streams may be from a single source. The oldest metamorphic rocks break down to moderately deep medium-textured red or yellow loams; granite rocks and acid volcanics to deeper red podzolic soils and xanthozems; and basalts to deep to very deep krasnozems. The high nutrient level of the basalt soils may have helped the rainforest to resist stress during the fluctuating climatic conditions of the Pleistocene glaciations. Moisture is the predominant influence on the coastal plains. As the drainage becomes poorer the soils change from gleyed podzols to humic gleys and acid peats. As usual with heavily leached soils of the wet tropics, most have extremely low contents of exchangeable calcium, magnesium and potassium, usually relatively high amounts of extractable aluminium and are poor in humus. Erosion can occur even under undisturbed rainforest.
Soil Map Of The Greater Wangetti Region (Northcote et al 1960-68)
ASRIS Soil Map Of The Greater Wangetti Region (2014)
