Spatial pattern of grazing pressure of red deer (Cervus elaphus) in Norway

Abstract

The dramatic increase of the red deer (Cervus elaphus) harvest in Norway the recent decades have led to concerns of possible oversized populations, and negative density effects on animal life history traits have been documented. However, few studies have been done on the state of the plant community. Measurements of accumulated browsing on important winter forage were conducted in two municipalities in Sogn and Fjordane, both to get better data on red deer diet and also in order to suggest whether such surveys may be a useful addition to monitoring animal performance in red deer management. I further quantified and analyzed the spatial patterns of browsing frequency of the highly selected rowan (Sorbus aucuparia) compared to the less selected blueberry (Vaccinium myrtillus) and birch (Betula sp.). I tested whether there were spatial variations in browsing frequency on a given plant species related to administrative units, habitat features and directly to variation in local population density or habitat use. A high utilization of low quality forage would indicate high population density relative to plant resources. From foraging theory, I predicted little spatial variation in browsing frequency of the highly selected rowan, and more variation for the assumed lower quality blueberry and birch. Administrative units explained little of the spatial variations in browsing frequency on rowan, while aspect, habitat forest type and productivity were the most important among factors describing the habitat. Slope and distance from arable land had a small effect on browsing frequency on rowan. There were some variations in browsing frequency on blueberry related to “Hunting area”, while “Block” explained most of the selection of birch. Of the parameters describing the habitat, habitat forest type and productivity were important for explaining spatial variation in browsing pressure on blueberry. Birch browsing frequency was affected by habitat productivity and altitude. Selection of all three plant species was positively correlated with red deer area use as assessed from faeces counts. Only blueberry showed variations in browsing frequency between “Hunting areas” which was related to local density, and I therefore argue that studies of browsing pressure on blueberry may be a useful tool in red deer management. This result also suggests that local variation in red deer density is not only due to habitat quality differences, but to local variation in management. Many plant species in Sogn and Fjordane are today heavily browsed, and further studies should try linking browsing pressure to changes in the plant community in order to assess broader ecosystem impacts.