Soils of the Brazilian Volcanic Islands

Abstract

The Brazilian oceanic islandsOceanic islands are true laboratories for Pedology, where certain specific conditions are never replicated in the continental portion. The soil genesis is affected by endemicEndemic soils flora and fauna, absence or extreme poverty of micro- and mesofauna, and environmental gradients in a very short distance, very recent and little altered volcanicVolcanic soils substrates, oceanic climate and biogeographic isolation. Therefore, the islands have great potential for soil endemisms, as in the case of the presence of Andossolos in Trindade. Neossolos, Cambissolos, Organossolos and Andossolos are the main soil classes in the Trindade island. In Noronha island, under a dry climate, AndosolsAndosols are absent, and most soils are Vertissolos, Cambissolos Háplicos eutróficos, Neossolos Regolíticos and Litólicos, fragmentários. Ornithogenic soils are very common in Noronha, Trindade and Abrolhos, and dominate the later Archipelago. Unusual carbonatic sands of marine origin are common parent materials in the coastal areas of oceanic islandsOceanic islands, and Neossolos Regolíticos, Flúvicos and Cambissolos were identified in both Noronha and Trindade islands, recording different conditions of pedogenesis. The carbonatic parent material and local climate are the main drivers of soil genesis, subordinated by biogenic and landform processes. All profiles have high Ca2+, base saturation, pH, CaCO3 equivalent and total Ca content, with calcite and aragonite minerals. Macromorphological and micromorphological features allow the detection of pedogenic carbonates in all soil, being more developed in Fernando de Noronha Calcisols, and partially dissolved in Trindade Calcisols. The contrasting landscape and climate evolution between these islands explain these differences. In the case of ornithogenic soils, the Brazilian oceanic islandsOceanic islands stand out for two important reasons: (1) the need to include ornithogenic phosphatization as a subgroup-level criterion in Brazilian Soil Classification System; (2) the possibility of using ornithogenic soils as environmental proxies that reveal the presence of ancient nests of oceanic birds, now extinct, by man, or by natural processes.