Impact of rainfall frequency and intensity on inter- and intra-annual satellite-derived EVI vegetation productivity of an Acacia caven shrubland community in Central Chile

Abstract

Seasonal precipitation is critical for springtime plant activity, and a direct connection may exist between the rainfall frequency and intensity with vegetation productivity in dryland ecosystems. This connection has been poorly quantified in the semi-arid Mediterranean region of Chile. In this work, we describe the effects of the monthly frequency (λ) and intensity (α) of rainfall events on two satellite-derived Enhanced Vegetation Index (EVI) descriptors: the time-integrated vegetation index (mEVI), a surrogate for total potential productivity, and the maximum vegetation index (iEVI), a surrogate for maximum photosynthetic activity, in a shrubland ecosystem dominated by Acacia caven. Time series analyses over a period of 15 years (2000–2014) were carried out for assessing their relationships and lags. Rainfall descriptors largely explained the temporal variation in vegetation productivity. Values of mEVI and iEVI showed a short-term statistical dependence of up to 4 months with precipitation frequency, meaning that vegetation productivity was delayed compared to the occurrence of rain events. This delay might be related to soils acting as water reservoirs being used by different plant types at different times and soil depths, i.e., herbs using water from the upper soil horizons with small lags in relation to rain pulses, while shrubs drawing water from deeper in the soil would exhibit greater range of lags. The asynchrony between rainfall events and suitable environmental conditions for growth, and the ability of plants to draw water at different soil depths with different lags may be an ecological adaptation to the high inter- and intra-annual rainfall variability.