In a summer pasture above tree-line in the Pyrenees, we studied, on ten plots arranged in three altitudinal series, the relations between ruminant grazing and some traits of the organisation of grass communities, as production, biomass, standing dead matter, litter, roots. In one of the three series, very homogeneous in other features outside altitude (aspect, slope, soil....), some characteristics are ordered with increasing elevation (litter rises potentially, and standing dead matter lineary); production fails lineary but with low significance.