Individual study: Influence of cattle stocking rate on browsing of Norway spruce Picea abies in subalpine wood pastures in Dischma valley, Grisons, Switzerland
Mayer A.C., Stöckli V., Konold W. & Kreuzer M. (2008) Influence of cattle stocking rate on browsing of Norway spruce in subalpine wood pastures. Agroforestry Systems, 66, 143-149
Around 15% of mountain forests in the Swiss Alps are summer-grazed by livestock, mainly cattle. In some areas this practice is viewed as detrimental due to supposed damage inflicted on trees as a consequence of cattle browsing, even though little is known about actual damage caused. In order to address this, the impact of grazing and browsing on Norway spruce Picea abies trees by cattle at different stocking rates were investigated in several subalpine wood pastures.
Study area: The study was carried out in 2000-2001 in the Dischma valley (46º46'N, 9º53'E), Canton of Grisons (Graubünden), eastern Switzerland. Seven areas between 1,560-2,000 m altitude covering all types of cattle-grazed wood pasture were investigated: 44% was woodland, 25% half woodland, half pasture and 31% open pasture (with scattered young trees and shrubs).
Influence of cattle stocking rate and wild ungulates: Cattle-grazing generally occurred for 3 months in summer (June to September). The stocking rate in 2000 ranged 0.4 livestock units (LU; i.e. 600 kg body weight)/ha to 2.8 LU/ha.
Damage due primarily to winter browsing by wild ungulates was also assessed; red deer Cervus elaphus only occasionally use the wood pastures for grazing during the summer; roe deer Capreolus capreolus are rare; chamois Rupicapra rupicapra (the only other ungulate present) occurs mainly at higher altitude in the summer, descending in winter. To assess their potential impact, four of the study areas where the last assessment of the tree condition after cattle grazing was made end of September 2000, were revisited at the end of May 2001 and tree condition again assessed (by various shoot length measurements and recording browsing damage). In total, 153 spruce trees (0.3 to 2.5 m in height) were sampled.
On average across all areas, 13% (20 of 153) of young spruce trees were damaged by browsing during the cattle grazing period in 2000; 4% were browsed on the apical shoot, 10% on lateral shoots. The browse rate ranged from 3% (in an area grazed by less than 1 LU/ha), to 22 and 23% (two areas grazed by 2.8 and 1.6 LU/ha, respectively). Variations in browse rate was almost completely explained by cattle stocking rate.
Browsing on the spruce trees during winter by wild ungulates was overall, 3-times higher (c. 60 trees damaged) than that attributed to cattle during summer.
In light of these results, the authors suggest that detrimental effects on young trees can be almost completely avoided if cattle stocking rates do not exceed 1 LU/ha.
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