Sensitivity of global terrestrial ecosystems to climate variability

Abstract

Here we present a novel, empirical approach to assess the relative sensitivity of ecosystems to climate variability, one property of resilience that builds on theoretical modelling work recognizing that systems closer to critical thresholds respond more sensitively to external perturbations 2 . We develop a new metric, the vegetation sensitivity index (VSI) which identifies areas sensitive to climate variability over the past 14 years. The metric uses time series data of MODIS-derived enhanced vegetation index (EVI) 3and three climatic variables that drive vegetation productivity 4 (air temperature, water availability and cloud cover). Underlying the analysis is an autoregressive modelling approach used to identify climate drivers of vegetation productivity on monthly timescales, in addition to regions with memory effects and reduced response rates to external forcing 5 . We find ecologically sensitive regions with amplified responses to climate variability in the arctic tundra, parts of the boreal forest belt, the tropical rainforest, alpine regions worldwide, steppe and prairie regions of central Asia and North and South America, the Caatinga deciduous forest in eastern South America, and eastern areas of Australia. Our study provides a quantitative methodology for assessing the relative response rate of ecosystems-be they natural or with a strong anthropogenic signature-to environmental variability, which is the first step toward addressing why some regions appear to be more sensitive than others and what impact this has upon the resilience of ecosystem service provision and human well-being.The rate and scale of projected climate changes in the 21st century are likely to have profound impacts on the functioning of Earth's ecosystems 6 . Much current understanding of how biodiversity will respond to climate change is based on responses to changes in mean Publisher: NPG; Journal: Nature: Nature; Article Type: Biology letter DOI: 10.1038/nature16986Page 2 of 25 climate state 7 . However, climate variability, and the related increases in extreme events in a warmer world 8 , has a strong influence on both the structuring and functioning of ecosystems [9][10][11] . Given the importance of identifying ecologically sensitive areas for ecosystem service provision and poverty alleviation 1 , a key knowledge gap exists in how to identify and then prioritize those regions that are most sensitive to climatic variability.Ecosystem response to variability in external forcing is a key component of resilience.Theory indicates that systems with lower resilience (that is, those with a high probability of crossing a threshold to an alternative state 12 ) experience amplified responses to disturbance and are more sensitive to environmental perturbations 2 . In addition, slower responses (identified through increased autocorrelation) may be evidence of reduced recovery rates in systems approaching critical transitions 13 . Therefore, identification of areas with high ecological sensitivity or reduced recovery rates is an importan...

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