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Grazing as a tool to create sward structures suitable to breeding birds.
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Edité par CCSD ; Wageningen Academic Publishers -
International audience. French wet grasslands support important populations of Lapwings and other waders. Grazing management is a key issue since these birds are very sensitive to sward structure (grass height heterogeneity). During three years, repeated measurements of sward height were conducted in a coastal marsh in order to assess the impact of different grazing regimes on sward during spring. Sward structure was characterized by six variables related to height classes and an index of heterogeneity. Grazing regimes were described by stocking rates per period and nitrogen index. Co-inertia analysis was performed. Total inertia was 0.57 and Monte Carlo simulation gave a probability p=0.000 to have a random co-structure between grazing regimes and sward structure. Three groups of fields were characterized. Fields showing a sward structure suitable for lapwings were winter grazed, low fertilized, then heavily grazed in early spring (i.e. strong defoliation limited re-growth until mid spring). Two other groups of fields had a higher height and it was shown that relation between heterogeneity and height was curvilinear. Taking into account wader habitat requirements calls attention to the postponed effects of winter grazing regimes. Thus, heterogeneity emerges as a new characteristic to steer. Its level depends on selective grazing by cattle and influences the sward growth: thresholds thus are to be investigated.
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