Résumé
CONTEXTIn cultivated landscapes, land use patterns related to the diversity of crops, their spatial arrangement into patches and their succession over several years influence many biophysical processes and the production of ecosystem services and disservices. Understanding the determinants of these patterns is a prerequisite for the development of acceptable alternative land use patterns. Most studies deem crop distribution patterns at the landscape level to be the result of individual allocations of crop successions to fields designed at the farm level. However, in some parts of the world, there are collective crop successions that apply to groups of adjacent fields on different farms.OBJECTIVEThe objective of this study was to examine the extent to which the spatiotemporal distribution of crops at the landscape scale relates to collective crop successions.METHODSThe study was based on a Mediterranean rainfed agricultural landscape (67.7 km2) located in northeastern Tunisia, in which collective successions respond to constraints related to agricultural land fragmentation. Combined with field mapping, remotely sensed land use time series were used to identify three-year crop sequences, classify them into crop succession types and identify clusters of adjacent fields with the same type of crop succession. We assumed that such a cluster was the result of a collective succession if the determinants of the individual crop succession locations did not explain its size (expressed in the number of fields). We related such determinants to the characteristics of the fields and their land-use environment and defined them statistically. Then, we developed a spatial permutation test to distinguish clusters resulting only from the determinants of the individual crop succession locations from those resulting from collective succession.RESULTS AND CONCLUSIONSThe results show that the collective successions mainly comprised biennial successions (wheat sown alternately with legumes, spices or forage crops). These successions were synchronized between adjacent fields based on wheat cultivation; all fields in the same cluster had wheat in the same year. Collective successions were secondarily comprised of fodder-dominant successions. These collective successions involved approximately 40% of the fields and their total area in the study area. These fields belonged to different clusters ranging in size from two to 96 adjacent fields.SIGNIFICANCEThe developed approach is a tool for mapping the likely presence of collective successions and considering this factor in the definition of sustainable land use scenarios at the landscape level for better soil and water management.