Tropical savannahs can be defined as mixed tree–grass systems, where the herbaceous layer is usually dominated by C4 grasses that use the C4 photosynthetic pathway to fix carbon, while trees use the ancestral C3 pathway. The lack of recognition of Asian savannahs as unique ecosystems distinct from forests, and the common misperception of savannahs as degraded forests pose significant conservation and management challenges.
Prof. Kyle W. Tomlinson of Xihsuangbanna Tropical Botanical Garden (XTBG) and his colleagues conducted a study to review the savannahs of Asia. Fossil and molecular evidence suggest that savannahs across Asia, and the savannah-adapted species associated with them, mostly existed before one million years, placing their existence prior to human modifications of the landscape.
Several lines of evidence suggest that savannahs were present in Asia before human arrival and were likely more extensive under past climates. The evidence lines include fossil evidence for C4 grasses and mammalian herbivores, climates similar to that of other savannahs, functional diversity that reflects selection under fire or mammalian herbivory, high diversity of C4 grasses and the presence of endemic species with life histories adapted to savannah environments.
Based on descriptions of extant vegetation across Asia, they have identified three major savannah types (tropical deciduous broadleaf savannahs, fine-leafed and spiny savannahs, and pine savannahs), where grasses form the dominant component of the herbaceous layer under open tree canopies, and which are associated with different tree lineages. Endemic plants and animals with life-histories characteristic of savannahs are found across the three savannah regions of Asia ((East, Southeast and South Asia). Asian savannahs house significant herbaceous diversity.
The researchers mapped the potential extent of Asian savannahs based on climatic domains of African, Australian and South American savannahs separately to gauge the most probable geographical distribution of Asian savannahs. They found that Asia supports larger areas with climates that are analogous to those occupied by African savannahs than either Australian or South American savannahs.
The researchers also reviewed the conservation and management challenges of Asian savannahs, which include inappropriate fire and herbivore management, land-use conversions to agriculture and tree plantations, severe invasions by exotic woody species and uncertain trajectories under changing climatic regimes.
The researchers suggested that there is an urgent need for identifying and mapping Asian savannahs, both potential and extant, not only for their effective management but also for a more nuanced understanding of tropical savannahs globally.
The study entitled “Savannahs of Asia: antiquity, biogeography, and an uncertain future” has been published online in Philosophical Transactions of the Royal Society B: Biological Sciences.
Contact
Kyle W. Tomlinson Ph.D Principal Investigator
Center for Integrative Conservation,Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, Yunnan,People's Republic of China
E-mail: kyle.tomlinson@xtbg.org.cn
