Abstract
Drylands are expected to be affected by greater global drought variability in the future; consequently, how dryland ecosystems respond to drought events needs urgent attention. In this study, the Normalized Vegetation Index (NDVI) and Standardized Precipitation and Evaporation Index (SPEI) were employed to quantify the resistance of ecosystem productivity to drought events in drylands of northern China between 1982 and 2015. The relationships and temporal trends of resistance and drought characteristics, which included length, severity, and interval, were examined. The temporal trends of resistance responded greatest to those of drought length, and drought length was the most sensitive and had the strongest negative effect with respect to resistance. Resistance decreased with increasing drought length and did not recover with decreasing drought length in hyper-arid regions after 2004, but did recover in arid and semi-arid regions from 2004 and in dry sub-humid regions from 1997. We reason that the regional differences in resistance may result from the seed bank and compensatory effects of plant species under drought events. In particular, this study implies that the ecosystem productivity of hyper-arid regions is the most vulnerable to drought events, and the drought–resistance and drought–recovery interactions are likely to respond abnormally or even shift under ongoing drought change.
Highlights
Increased drought events due to rising global temperatures has caused worldwide concern, even though droughts can be mitigated by fluctuations of precipitation [1,2,3]
Since greater drought variability is expected in the coming century [12,13,14], understanding the resistance of dryland ecosystems to drought events in a long-term time series is crucial in predicting the response of dryland ecosystems to droughts [15,16]
Temporal trends of resistance and driving factors under increased drought variability have rarely been examined because the ‘extremeness’ of drought events are highly dependent on historic droughts and what the ecosystem and its component species have experienced in the past [15,35,62]
Summary
Increased drought events due to rising global temperatures has caused worldwide concern, even though droughts can be mitigated by fluctuations of precipitation [1,2,3]. An alleviating trend of droughts has been recorded in some regions, including some drylands, in the last decade [4,5,6,7,8]. Such fluctuations in droughts, that is, prolonged increases in droughts followed by an alleviation, provides the basis for a natural study in predicting the response of ecosystems to drought events [9]. Drylands, comprising hyper-arid, arid, semi-arid, and dry sub-humid ecosystems, may differ greatly in their resistance to drought events [34]
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