Long-term browsing impact around diversionary feeding stations for moose in Southern Norway

Sammendrag

Diversionary winter feeding of browsing ungulates is an increasingly common management practice although evidence for its efficacy to reduce excessive browsing in forests of commercial or conservational value remains ambiguous. Moreover, comparative estimates of browsing pressure following long-term winter feeding are currently lacking. We quantified spatiotemporal changes in browsing pressure of moose (Alces alces L.) on commercial and non-commercial tree species around 30 feeding stations after 15-20 years of winter feeding. We compared results with browsing pressure indices recorded at the same feeding stations 10 years previously. If moose numbers around feeding stations have increased over time we predicted (P1): leader stem browsing and lateral twig browsing to have increased in intensity at a fine spatial scale (≤ 200 m from feeding station) and furthermore, (P2) a high occurrence of intense moose browsing up to 1 km from feeding stations. Despite 2-3 times higher faecal pellet group densities in the vicinity of feeding stations, leader stem browsing increased only on the commercially valuable Norway spruce (Picea abies (L.) Karst), a species normally avoided by moose.Lateral twig browsing largely decreased rather than increased within 200 m of feeding stations, defying the predictions in P2. At a broader scale (≥ 200 m to 1 km from feeding stations), leader stem browsing was high on all tree species (ca. 60% of available stems browsed) as expected from P2, except for Norway spruce. Furthermore, peak browsing on lateral twigs of Scots pine (Pinus sylvestris L.) occurred further from feeding stations after 15-20 years of winter feeding than 10 years previously.. Browsing pressure on active feeding stations (n = 18) was comparable to inactive feeding stations (n = 12), suggesting the occurrence of rebrowsing. Long-term diversionary winter feeding of moose has serious implications for the intensity of fine-scale browsing pressure, which may lead to resource depletion close to feeding stations followed by high browsing pressure at distances further away from feeding stations. Our study emphasizes the importance of considering the longevity of a winter feeding programme at its inception. Long-term diversionary feeding may increase the size required for sacrifice areas if feeding is practiced in fixed locations.