Abstract
A major disturbance in nature, drought, has a significant impact on the vulnerability and resilience of semi-arid ecosystems by shifting phenology and productivity. However, due to the various disturbance mechanisms, phenology and primary productivity have remained largely ambiguous until now. This paper evaluated the spatio-temporal changes of phenology and productivity based on GIMMS NDVI3g time series data, and demonstrated the responses of vegetation phenology and productivity to drought disturbances with the standardized precipitation evapotranspiration index (SPEI) in semi-arid ecosystems of northern China. The results showed that (1): vegetation phenology exhibited dramatic spatial heterogeneity with different rates, mostly presented in the regions with high chances of land cover type variation. The delayed onset of growing season (SOS) and advanced end of growing season (EOS) occurred in Horqin Sandy Land and the eastern Ordos Plateau with a one to three days/decade (p < 0.05) rate and in the middle and east of Inner Mongolia with a two days/decade rate, respectively. Vegetation productivity presented a clear pattern: south increased and north decreased. (2) Spring drought delayed SOS in grassland, barren/sparsely vegetated land, and cropland, while autumn drought significantly advanced EOS in grassland and barren/sparsely vegetated lands. Annual drought reduced vegetation productivity and the sensitivity of productivity regarding drought disturbance was higher than that of phenology.
Highlights
Drought has affected most regions of East Asia in the early 21st century [1,2]
Due to different response mechanisms to drought among vegetation species, the impacts of drought on ecosystem functions retain a large amount of uncertainty, regarding productivity(e.g., Net Primary Productivity, NPP) and vegetation phenology [13]
The climatic variation or dry-wet conditions in the study area were characterized by precipitation, temperature, and standardized precipitation evapotranspiration index (SPEI) values
Summary
Drought has affected most regions of East Asia in the early 21st century [1,2]. The frequency of extreme climatic events will greatly increase for the 40 years in Northern China, most notably in semi-arid regions [3,4]. There will probably be an enhancement of the drought sensitivity of ecosystems [5], reduction in productivity and biodiversity, and change of vegetation species composition [6,7,8,9]. It is vital to clearly understand the disturbance mechanisms of drought on ecosystems in order to cope with extreme drought events in the future. Carbon and hydrology processes of terrestrial ecosystems are the main pathways disturbed by drought [11], in a water-limited semi-arid ecosystem. Moderate drought reduces the photosynthesis rate via stomatal control and improves water use efficiency with physiological adaption of vegetation at an individual level [7,11]. Productivity and biodiversity significantly decrease with reduced photosynthesis and evapotranspiration rates [6,11,12]. Due to different response mechanisms to drought among vegetation species, the impacts of drought on ecosystem functions retain a large amount of uncertainty, regarding productivity(e.g., Net Primary Productivity, NPP) and vegetation phenology [13]
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