Experimental determination of the effects of cattle stocking density and grazing period on forest regeneration on a subalpine wood pasture

The influence of cattle stocking density and the length of the grazing period on the extent of tree damage on subalpine wood pastures was assessed. An experiment was carried out on four adjoining fields, grazed by zero, three, six and nine heifers. The fields were grazed until herbage resources were exploited. Spruce seeds were seeded, spruce saplings (Picea abies (L.) Karst. (average height of 14 cm) as well as young spruces, larches (Larix decidua Miller) and rowans (Sorbus aucuparia L.) of 42 cm height were planted. The experimental site was situated at 1900 m a.s.l.; 20% of the area was forest. Browsing and other damage on planted spruce saplings and young spruces, larches and rowans were recorded. The germination rate of spruce seeds was recorded and the survival rate of the seedlings germinated was analysed. The heifers spent around 30% of the time under the tree canopies, both for resting and grazing, instead of the expected 20% based on the relative forest cover. Since the herbage quality was found to be similar in the forest and on the open pasture and since there was no effect of stocking density on herbage intake and digestibility as assessed in the first week of the experiment, the effects on the trees were considered independent from herbage quality. Grazing at high stocking densities enhanced the germination of spruce seedlings. Rowan was browsed most frequently, depending on stocking density and grazing period. Also larch was browsed frequently. With increasing grazing time, even spruces of 14 cm and 42 cm height were frequently browsed, but there was no clear relationship to stocking density. The observations showed that individual animals that have developed a specific preference for spruce needles may play a decisive role in the extent of browsing on spruce. In conclusion, guidelines for a sustainable use of subalpine wood pastures require restrictions either in stocking density or in the length of the grazing period or in both. Détermination expérimentale des effets de la densité du bétail et de la durée de pacage sur la régénération des forêts dans un système sylvopastoral. Cette étude a pour but d'évaluer l'influence de la densité du bétail et de la durée de pacage sur l'étendue des dommages occasionnés aux arbres situés dans les pâturages boisés. Pour cette expérience, un pâturage a été divisé en 4 sections pâturées par 0, 3, 6 et 9 génisses respectivement. Ces pacages ont été pâturés jusqu'à l'exploitation totale de leurs ressources.