Grassland afforestation impact on primary productivity: a remote sensing approach

Abstract

AbstractQuestionHow is the magnitude and seasonality of carbon uptake affected by the replacement of native grasslands by eucalyptus plantations?LocationRío de la Plata Grasslands in Argentina and Uruguay.MethodsA total of 115 paired sites of fast‐growingEucalyptus grandisplantations and adjacent grasslands were used to characterize the magnitude and seasonality of (1) radiation interception by canopies and (2) above‐ground net primary productivity based on a time series ofMODIS‐derived normalized difference vegetation index (NDVI). The response ofNDVIto precipitation was explored across temporal scales.ResultsNDVIin afforested vs. grassland plots presented higher annual averages (1.3‐fold), lower seasonal ranges (average relative range of 0.11 vs. 0.29) and delayed growing seasons (2‐month shift). Temporally,NDVIwas positively associated with precipitation input, showing a correlation with longer periods of precipitation accumulation in tree plantations compared to grasslands (> 7 vs. 2–3 months). Estimated average annual above‐ground net primary productivity (ANPP) almost quadrupled as a consequence of replacing grasslands by tree plantations (∼4 vs. ∼17 Mg dry matter. ha−1·yr−1), and this difference was evidenced throughout the whole study period.ConclusionsAfforested grasslands intercept more radiation and have higher and more stableANPPthroughout the year, probably as a result of major changes in leaf phenology and root distribution patterns, which in turn allowed better access to water. Changes in carbon uptake can influence climate/biosphere feedbacks and should be considered in land‐use planning, especially when grassland afforestation is recommended as a tool to mitigate global warming.