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.
Highlights
Ultramafic soils are weathered products of lithologies, such as peridotite and serpentinite bedrock, consisting predominantly of ferromagnesian silicate minerals (Cardace et al 2014; Moores 2011)
This review examines the literature on the geoecology of ultramafic areas in South and Southeast Asia, covering India, Pakistan, and Sri Lanka to the west, Myanmar and Cambodia to the north, and Malaysia, Indonesia, and the Philippines to the east (Fig. 1; Table 1); all of which lie on the western side of Lydekker’s line and share a similar climate
Information gaps and future directions Ultramafic outcrops are natural laboratories for experimental and applied research in a wide range of disciplines. They provide numerous opportunities for collaborations among geologists, pedologists, botanists, zoologists, microbiologists, and land managers focusing on conservation and restoration research
Summary
Ultramafic soils are weathered products of lithologies, such as peridotite and serpentinite bedrock, consisting predominantly of ferromagnesian silicate minerals (Cardace et al 2014; Moores 2011). Combined with an additional 40 taxa reported from three other sites surveyed by Rajakaruna and Bohm (2002), the total ultramafic flora of Sri Lanka stands at a mere 107 species, compared to many-fold more documented from other sites in Southeast Asia (van der Ent et al 2015a). Sri Lanka’s ultramafic outcrops and their flora, compared with ultramafic floras of Southeast Asia and Australia-Pacific region (van der Ent et al 2015c, d), have received relatively little attention partly because they do not harbor any endemic species nor many metal hyperaccumulators (Chathuranga et al 2015).
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