Dynamics of terrestrial ecological indicators in East Asia during last decades

Background/Question/Methods

The vulnerability of ecosystems has become a key issue both in assessing the impact of climate change and in planning the adaptation strategies to climate change. The vulnerability of ecosystems is often described by various ecological indicators concerning the biogeochemical cycles, such as evapotranspiration (ET) and runoff (RO) in the water cycle, net primary productivity (NPP), net ecosystem productivity (NEP) and net biome productivity (NBP) in the carbon cycle, ammonium (NH⁴⁺), nitrites (NO^2-), and nitrates (NO^3-) in the nitrogen cycle. In this study, we analyzed the dynamics of these ecological indicators in last 5 decades by employing a sophistical ecosystem model, Biome-BGC. The model inputs include the data of land cover, soil properties as well as meteorological data, such as daily maximum, minimum and average air temperature (Ta, °C), daily total precipitation (P, cm), daylight average vapor pressure deficit (VPD, Pa), shortwave radiation (Rs, W/m²) and day length (L, s) during 1961-2010 at more than 400 stations in East Asia. The average Ta of all these stations increased about 1.4°C in last 50 years, which is larger than that of global average, while the other climate factors, such as P and Rs have no obvious tendency of increasing or decreasing. Comparison between the simulated values with observed data measured by five flux towers, which we established in five typical ecosystems in East Asia, suggested that the model can predict both the water and carbon cycles reasonably in both natural and agricultural ecosystems under the consideration of the effects of anthropogenic forcing, such as increasing CO₂ concentrations, fertilizer application and irrigation.

Results/Conclusions

Model simulation shows that the ecological indicators, such as ET, NPP, and NEP are highly sensitive to climate change in natural ecosystems, particularly in the transitional regions between geographical zones, such as the region surrounding deserts in Mongolia Plateau and Tibet Plateau. It also shows that the average annual ET, GPP and NPP of all stations has been increasing, while the annual NBP has been decreasing during last several decades. Comparing with different climate zones, it is found that both NPP and NBP has been decreasing in humid areas in the southeastern part of East Asia, but has been increasing in arid and semi-arid areas in the northwestern part. Comparing with different ecosystems, it is found that NPP and NBP have been increasing in forest ecosystem, while decreased in grassland ecosystems in last decades.