CONICET | Buscador de Institutos y Recursos Humanos

Land-cover change associated with agriculture has had an enormous effect on thestructure and functioning of temperate ecosystems. However, the empiricalevidence for the impact of land use on ecosystem functioning at the regionalscale is scarce. Most of our knowledge on land-use impact has been derived fromsimulation studies or from small plot experiments. In this article we studied theeffects of land use on (i) the seasonal dynamics and (ii) the interannual variabilityof the Normalized Difference Vegetation Index (NDVI), a variable linearly relatedto the fraction of the photosynthetically active radiation (PAR) intercepted by thecanopy. We also analysed the relative importance of environmental factors andland use on the spatial patterns of NDVI. We compared three cultivated landcovertypes against native grasslands. The seasonal dynamics of NDVI was usedas a descriptor of ecosystem functioning. In order to reduce the dimensionality ofour data we analysed the annual integral (NDVI-I), the date of maximum NDVI(DMAX) and the quarterly average NDVI. These attributes were studied for7 years and for 346 sites distributed across eastern Colorado (USA).Land use did modify ecosystem functioning at the regional level in easternColorado. The seasonal dynamics of NDVI, a surrogate for the fraction of PARintercepted by the canopy, were signi®cantly altered by agricultural practices.Land use modi®ed both the NDVI integral and the seasonal dynamics of thisspectral index. Despite the variability within land-cover categories, land use wasthe most important factor in explaining regional differences of the NDVIattributes analysed. Within the range of environmental conditions found in easternColorado, land use was more important than mean annual precipitation, meanannual temperature and soil texture in determining the seasonal dynamics ofNDVI.

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