Abstract
Within the context of climate change, it is of utmost importance to quantify the stability of ecosystems with respect to climate anomalies. It is well acknowledged that ecosystem stability may change over time. As these temporal stability changes may provide a warning for increased vulnerability of the system, this study provides a methodology to quantify and assess these temporal changes in vegetation stability. Within this framework, vegetation stability changes were quantified over Australia from 1982 to 2006 using GIMMS NDVI and climate time series (i.e., SPEI (Standardized Precipitation and Evaporation Index)). Starting from a stability assessment on the complete time series, we aim to assess: (i) the magnitude and direction of stability changes; and (ii) the similarity in these changes for different stability metrics, i.e., the standard deviation of the NDVI anomaly (SD), auto-correlation at lag one of the NDVI anomaly (AC) and the correlation of NDVI anomaly with SPEI (CS). Results show high variability in magnitude and direction for the different stability metrics. Large areas and types of Australian vegetation showed an increase in variability (SD) over time; however, vegetation memory (AC) decreased. The association of NDVI anomalies with drought events (CS) showed a mixed response: the association increased in the western part, while it decreased in the eastern part. This methodology shows the potential for quantifying vegetation responses to major climate shifts and land use change, but results could be enhanced with higher resolution time series data.
Highlights
Ecosystems provide important services to man and society, such as water purification, regulation of climate, pests and diseases, pollination, provision of wildlife habitat, biodiversity conservation and the delivery of wood and products through ecosystem functions, such as biomass production [1]
In order to frame temporal stability changes, each of the stability metrics were first derived over the complete time period
These metrics illustrate that vegetation response clearly differs spatially and is linked to the land cover types and environmental conditions (Figures 5 and 6)
Summary
Ecosystems provide important services to man and society, such as water purification, regulation of climate, pests and diseases, pollination, provision of wildlife habitat, biodiversity conservation and the delivery of wood and products through ecosystem functions, such as biomass production [1]. Changes in average climate conditions, as well as increased frequency of climate extremes, suggested by the latest IPCC scenarios, threaten the stable delivery of these services [2]. Understanding the stability of these ecosystem services is of critical. Methods that examine the stability of natural and productive systems using remote sensing can be useful for this kind of assessment. At the moment a disturbance occurs, the vegetation state may change, where the ability of the ecosystem to withstand the disturbance is referred to as resistance. The ecosystem may return to its original state. The speed at which the ecosystem returns is denoted by engineering resilience. Sometimes the disturbance is strong enough or changing conditions have diminished its engineering resilience, and the system might change its regime, i.e., find a new stable state. Variance denotes the total variability of the system in response to environmental anomalies [3]
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