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 Printable version |
Itinerant grazing in the lower Seine Valley (France): an agronomic and ecological necessity |
Cahiers Agricultures. Volume 8, Number 6, 486-97, Novembre - Décembre 1999, Synthèse
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 Résumé
Article gratuit
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Author(s) : Thierry Dutoit |
Summary : Since the late 1960s, conservation management systems have been developed in Europe for flora and fauna with the aim of preserving biological diversity in remarkable natural areas. Agriculture-based techniques such as grazing and mowing are mostly used in natural reserves and regional natural parks. They were initially implemented without any agricultural reference, while today conservation management systems have to cope with landscape shaping due to agricultural practices and include up-to-date knowledge on leading and feeding herds. In the Seine Valley, we studied the resoration of old agricultural fallow lands, such as wet meadows (Mannevilles Nature Reserve) and dry calcareous grasslands (Saint-Adrien nature reserve) (Figure 1) by monitoring the evolution of former agricultural systems (using historical ecology methods, see Box 1), and by evaluating the fodder quality of wet meadows and dry grasslands through mineral analyses. In the lower Seine Valley, dry calcareous grasslands represent a threatened species-rich ecosystem (Box 2) that originated from neolithic forest clearance, followed by several centuries of use as sheep walks. Since the Dark Ages, most of the calcareous grasslands studied were grazed by sheep rather than cattle (Photos 1 &\; 2). The grazing area of these herds included roadside verges, cereal stubble, temporally abandoned fields, wet meadows near the Seine Valley (Photo 3), and woodlands, especially during winter. A few goats were mixed with sheep to guide flocks and grazing was supplemented by browsing in shrubby areas (Photo 3). An essential feature of this type of sheep husbandry was that the animals only grazed for a few hours a day. The rest of the time they were kept in a special kind of stable (Photo 4), including a mobile fence that was moved daily so that the the entire dry grassland would benefit from the manure produced. Formerly, meat and wool were therefore not the only major products of sheep husbandry and for a long time dung was even more important. When the grazing intensity was insufficient to control the extension of tussock species and shrub encroachment, shepherds undertook controlled burning in the early spring. After WWII, dry calcareous grasslands of the lower Seine Valley were no longer an important food resource for agriculture and were progressively abandoned. The Vernier Bog nature reserve (Box 3) provides a good example of the evolution of former agricultural systems in the wet meadows of the lower Seine Valley. This ecosystem was characterized by the establishment of highly productive vegetation with low herbaceous plants, biologically diversified and typical of marshes. In the Dark Ages, Vernier Bog was drained (Photo 5) and the wet meadows were mostly used for cattle grazing (Photo 6) or peat extraction. In the middle of the 20th century, the cessation of pasturing and the lack of cattle herds led to a rapid change in the ecosystem from species-rich wet meadows to poor shrub and forest communities. In both wet meadows and dry grasslands, a series of natural changes occurred in the absence of grazing, prompting natural successions which led to plant communities of shrubs (Photos 7 &\; 8) and/or species-poor coarse grasslands. The main results of mineral analyses of these poor coarse turfs (wet and dry) are: i) a clear distinction between the nutrient contents of the dominant species (Figure 2)\; ii) a contrasted evolution of agronomic value and mineral contents during a seasonal vegetation period (Figures 3 &\; 4)\; and iii) a yield decrease in chalk grassland turf during summer (Figure 5). A review of historical research records and the results of mineral analyses of plants in wet meadows and dry grasslands of the Seine Valley showed that a return to an itinerant grazing scheme is essential from ecological and agronomic viewpoints. When biological conservation is the management goal, grazing systems should take the low nutritional value of wet and dry grassland into account, along with the availability of the different chemical elements in palatable and unpalatable herbaceous species and shrubs. Species-rich wet meadows and dry calcareous grasslands could therefore be restored via an itinerant grazing system with rustic animals (highland cattle, mergelland sheep), when periods of grazing and stocking rates are in agreement with plant diversity and animal health. Unimproved races of sheep or cattle could survive in wet meadows and dry grasslands without a large supply of extra food because these animals feed on coarse grasses forsaken by improved races. At present, such systems are being developed in different regions of northwestern Europe, especially with the implementation of agri-environmental measures in the "management fund for rural area" framework. |
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