Mapping farmland abandonment and recultivation across Europe using MODIS NDVI time series

Farmland abandonment is a widespread land-use change in temperate regions, due to increasing yields on productive lands, conservation policies, and the increasing imports of agricultural products from other regions. Assessing the environmental outcomes of abandonment and the potential for recultivation hinges on incomplete knowledge about the spatial patterns of fallow and abandoned farmland, especially at broad geographic scales. Our goals were to develop a methodology to map active and fallow land using MODIS Normalized Differenced Vegetation Index (NDVI) time series and to provide the first European-wide map of the extent of abandoned farmland (cropland and grassland) and recultivation. We used a geographically well-distributed training dataset to classify active and fallow farmland annually from 2001 to 2012 using a Random Forests classifier and validated the maps using independent observations from the field and from satellite images. The annual maps had an average overall accuracy of 90.1% (average user's accuracy of the fallow class was 73.9%), and we detected an average of 128.7 million hectares (Mha) of fallow land (24.4% of all farmland). Using the fallow/active time series, we mapped fallow frequency and hotspots of farmland abandonment and recultivation of unused farmland. We found a total of 46.1 Mha of permanently fallow farmland, much of which may be linked to abandonment that occurred after the dissolution of the Eastern Bloc. Up to 7.6 Mha of farmland was additionally abandoned from 2001 to 2012, mainly in Eastern Europe, Southern Scandinavia, and Europe's mountain regions. Yet, recultivation is widespread too (up to 11.2 Mha) and occurred predominantly in Eastern Europe (e.g., European Russia, Poland, Belarus, Ukraine, and Lithuania) and in the Balkans. We also tested the robustness of our maps in relation to different abandonment and recultivation definitions, highlighting the usefulness of time series approaches to overcome problems when mapping transient land-use change. Our maps provide, to our knowledge, the first European-wide assessment of fallow, abandoned and recultivated farmland, thereby forming a basis for assessing the environmental outcomes of abandonment and recultivation and the potential of unused land for food production, bioenergy, and carbon storage.