Effects of simulated moose Alces alces browsing on the morphology of rowan Sorbus aucuparia

In much of northern Sweden moose Alces alces browse rowan Sorbus aucuparia heavily and commonly revisit previously browsed plants. Repeated browsing of rowan by moose has created some concern for its long-term survival in heavily browsed areas. We therefore measured how four years of simulated moose browsing at four population densities (0, 10, 30 and 50 moose/1,000 ha) changed plant height, crown width, available bite mass, the number of bites per plant and per plant forage biomass of rowan saplings. Increased biomass removal led to a significant decline in plant height (P < 0.001), but a significant increase in the number of bites per plant (P = 0.012). Increases in the number of bites per plant more than compensated for weak decreases in bite mass, leading to a weak increase in per plant forage biomass (P = 0.072). With the decline in plant height and increase in the number of stems per plant, a greater number of bites remain within the height reach of moose relative to unbrowsed controls. Moose therefore stand to benefit from revisiting previously browsed plants, which may result in feeding loops between moose and previously browsed rowan saplings.