Low intensities of red deer browsing constrain rowan growth in mature boreal forests of western Norway

摘要

Browsing by ccrvids plays a key role in structuring forest ecosystems and dynamics. Many boreal forest systems arc managed for timber resources, and at the same time the wild ccrvid populations arc also Harvested. Thus, the determination of sustainable densities of ccrvids for the purpose of forest and game management is challenging. In this study we report on a red deer (Cervus elaphus) cxclosurc experiment in the mature forests of Western1 Norway. Ten pairs of cxclosurcs and browsed plots were initiated in 2008. The rate of browsing and height growth of marked individuals was recorded annually, and the total densities of all tree species assessed over the following 4 y. We found that height growth of rowan (Sorbus aucuparia) saplings (1 m tall), the most numerous tree species at the site, was prevented when 20% of the shoots were browsed. Outside of the cxclosurcs, net height growth of rowan saplings tended to be positive when trees were below 40 cm in height, but growth was constrained in rowansaplings over this height. The density of rowan also increased in both treatments, showing that recruitment was occurring, but the increase was greater where browsed than in the cxclosurc. The increase in density of rowan, combined with the curtailment of height growth in the presence of red deer, serves to create a carpet of short stature rowan saplings. This has parallels with the browsing lawn concept, but it seems to occur in interaction with snow depth; individuals protruding above the snow layer arc likely to be browsed during the winter, whilst smaller individuals arc protected during this season, when browsing is at its peak.