Ultramafic geoecology of South and Southeast Asia

Abstract

Globally, ultramafic outcrops are renowned for hosting floras with high levels of endemism, including plants with specialised adaptations such as nickel or manganese hyperaccumulation. Soils derived from ultramafic regoliths are generally nutrient-deficient, have major cation imbalances, and have concomitant high concentrations of potentially phytotoxic trace elements, especially nickel. The South and Southeast Asian region has the largest surface occurrences of ultramafic regoliths in the world, but the geoecology of these outcrops is still poorly studied despite severe conservation threats. Due to the paucity of systematic plant collections in many areas and the lack of georeferenced herbarium records and databased information, it is not possible to determine the distribution of species, levels of endemism, and the species most threatened. However, site-specific studies provide insights to the ultramafic geoecology of several locations in South and Southeast Asia. The geoecology of tropical ultramafic regions differs substantially from those in temperate regions in that the vegetation at lower elevations is generally tall forest with relatively low levels of endemism. On ultramafic mountaintops, where the combined forces of edaphic and climatic factors intersect, obligate ultramafic species and hyperendemics often occur. Forest clearing, agricultural development, mining, and climate change-related stressors have contributed to rapid and unprecedented loss of ultramafic-associated habitats in the region. The geoecology of the large ultramafic outcrops of Indonesia’s Sulawesi, Obi and Halmahera, and many other smaller outcrops in South and Southeast Asia, remains largely unexplored, and should be prioritised for study and conservation.

Predominant colonization of Malesian mountains by Australian tree lineages

“…After c. 10 My of isolation, the Australian plate started to collide with the Southeast Asian plate and island arcs from several Pacific plates around the Oligocene‐Miocene boundary (c. 25–20 Ma). The exact geological processes involved were complex both in time and space but, together, caused extensive uplifting at the northern margin of the Sahul Shelf in what is today New Guinea, and shaped the young islands comprising Wallacea (Sulawesi, Maluku Islands, Lesser Sunda Islands) including some of the largest areas of ultramafic bedrock worldwide (Galey, van der Ent, Iqbal, & Rajakaruna, ; Hall, , ). At the same time, temperatures rose again and moist tropical habitats expanded in Australia until the mid‐Miocene climatic optimum.…”

“…Despite intervals of strong climatic oscillations, since the middle Eocene tropical rain forests have covered parts of Sundaland, especially in what today is the island of Borneo. Hence, since the large-scale onset of the MFI c. 23 Ma, there has been a large source population of plants adapted to tropical rainforest habitats in Sundaland (Hall, 2013;Morley, 2012 (Galey, van der Ent, Iqbal, & Rajakaruna, 2017;Hall, 2013Hall, , 2017 was offset in Australia by the continued rafting towards the equator, at least in the north but intensive aridification occurred, leading to an overall contraction of mesic biomes, which remained mostly in montane refugial areas along the eastern coast of the continent and in eastern New Guinea, where mountains had been present since the early Oligocene (Bryant & Krosch, 2016;Byrne et al, 2011;Macphail, 2007;Martin, 2006;Quarles van Ufford & Cloos, 2005).…”

Growth effects in tropical nickel‐agromining ‘metal crops' in response to nutrient dosing

“…Unlike P. rufuschaneyi, which is restricted to only two localities in Sabah, Rinorea cf. bengalensis is widespread in Southeast Asia (Brooks and Wither, 1977;Galey et al, 2017). It occurs on both ultramafic and non-ultramafic soils, with only the populations on ultramafic soils hyperaccumulating Ni, making it a facultative hyperaccumulator (Brooks and Wither, 1977).…”

Rock-type control of Ni, Cr, and Co phytoavailability in ultramafic soils

“…Whittaker 1954;Main 1974;Main 1981;Galey et al 2017;Gonneau et al 2017;Van der Ent et al 2017;Van der Ent et al 2018). Although knowledge about relationships between metals with other elements or factors in plants is broad, it is still difficult to final identify the causes of differences in Ni, Cr, and Co content in plants from Polish ultramafic soils.…”