Consequences of less intensive farming on the landscape: an example of vegetation dominance by Chaerophyllum aureum in the meadows of a Pyrenean valley in France

The impact of agricultural practices on the dynamics of weed invasion in a rural landscape was studied by describing the spatial distribution of Chaer ophyllum aureum populations colonising less intensive managed hay meadows. Polyphenol compounds were used as individual markers to identify the struct ure of C aureum diversity, in terms of its scale and patterns, within and b etween fields along the bottom of a Pyrenean valley. The results revealed, firstly, the existence of a dominant 'genotype' successfully colonising the entire area, and secondly, the maintenance of high levels of polyphenol di versity within five different populations. This spatial arrangement of 'gen etic' population diversity was obviously not related to the natural reprodu ction and dispersal patterns of this species, but to human practices of hay production, the principal effect of which is to mix seeds of different gen etic origin and thus accelerate and amplify the colonisation process of ada pted 'genotypes'.