Abstract
Abstract. South Asian vegetation provides essential ecosystem services to the 1.7 billion inhabitants living in the region. However, biodiversity and ecosystem services are threatened by climate and land-use change. Understanding and assessing how ecosystems respond to simultaneous increases in atmospheric CO2 and future climate change is of vital importance to avoid undesired ecosystem change. Failed reaction to increasing CO2 and climate change will likely have severe consequences for biodiversity and humankind. Here, we used the adaptive dynamic global vegetation model version 2 (aDGVM2) to simulate vegetation dynamics in South Asia under RCP4.5 and RCP8.5, and we explored how the presence or absence of CO2 fertilization influences vegetation responses to climate change. Simulated vegetation under both representative concentration pathways (RCPs) without CO2 fertilization effects showed a decrease in tree dominance and biomass, whereas simulations with CO2 fertilization showed an increase in biomass, canopy cover, and tree height and a decrease in biome-specific evapotranspiration by the end of the 21st century. The predicted changes in aboveground biomass and canopy cover triggered transition towards tree-dominated biomes. We found that savanna regions are at high risk of woody encroachment and transitioning into forest. We also found transitions of deciduous forest to evergreen forest in the mountain regions. Vegetation types using C3 photosynthetic pathway were not saturated at current CO2 concentrations, and the model simulated a strong CO2 fertilization effect with the rising CO2. Hence, vegetation in the region has the potential to remain a carbon sink. Projections showed that the bioclimatic envelopes of biomes need adjustments to account for shifts caused by climate change and elevated CO2. The results of our study help to understand the regional climate–vegetation interactions and can support the development of regional strategies to preserve ecosystem services and biodiversity under elevated CO2 and climate change.
Highlights
Global climate has been identified as the primary determinant of large-scale natural vegetation patterns (Overpeck et al, 1990)
The model performed well in areas with higher fractional cover of natural vegetation, such as the Himalayas, Western Ghats and the northeast of the region, the model overestimated biomass and canopy area in the Brahmaputra basin, which lies between 28–34◦ N and 90–96.5◦ E in the northeast of the study region (Fig. 1a, c, Kumar et al, 2020)
We investigated the impact of eCO2 and climate change on South Asian biomes and found that climate change and CO2 fertilization in combination are substantial drivers of biome change and that elevated CO2 concentrations altered the climatic envelope of biomes in addition to causing increases in biomass, tree height and canopy cover
Summary
Global climate has been identified as the primary determinant of large-scale natural vegetation patterns (Overpeck et al, 1990). Climate change has affected global vegetation pattern in the past and caused numerous shifts in plant species distribution over the last few decades (Chen et al, 2011; Thuiller et al, 2008). It is expected to have even more pronounced effects in the future and may lead to drastically increasing species extinction rates in various ecosystems (Brodie et al, 2014). Rising CO2 is expected to alter distributions of plant species and ecosystems (Parry et al, 2007) both indirectly through its influence on global temperatures and precipitation patterns (Cao et al, 2010), two main drivers of vegetation dynamics, and directly via its physiological effects on plants (Nolan et al, 2018)
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