Year-to-year variability of NDVI in croplands and grasslands across a regional grasslands-forest ecotone in Central Alberta, Canada

The interannual variability of NDVI (STD(t)) was calculated for each semi-monthly interval over the period 1982-2006, using GIMMS NDVI images of Alberta, Canada. Forested areas usually show maximum interannual variability in spring and fall (temperature dependence), while grasslands have maximum variability in summer (moisture dependence). In moister areas., grasslands show less summer variability and approach the forest pattern. Croplands mimic the temporal pattern of grasslands located in the same ecoregion. In the ecotone between naturally forest and naturally grassland ecoregions, crops show greater summer variability than their nearby grasslands, indicating a greater sensitivity by crops than by grasslands to moisture stress. This pattern divergence may be used to show crop particularly sensitive to drought; this would be particularly useful where detailed local meteorological and crop data are not compiled. Changes in patterns over time can also help plan agricultural adaptation to climate change in a spatially complete form.