Age- and stage-based bud demography of Salix arctica under contrasting muskox grazing pressure in the High Arctic

We compared the bud demography of deciduous, dioecious Salix arctica Pall. plants between vegetation of contrasting muskox grazing pressure, and between female, male and vegetative plants, on central Ellesmere Island, Canada. We developed age- and stage-based transition matrix models in order to investigate the contribution of annual shoot generations, and the significance of different bud types (dormant, vegetative, catkin, eaten) to bud population growth. The bud population growth rates were higher in all shoot generations of the grazed plants compared with the ungrazed plants. This was a consequence of a higher bud production rate in the grazed plants, whereas the bud survival rate was similar among all plants. Vegetative plants had the highest bud population growth rates, but the difference was significant only between vegetative plants and females in the grazed habitat. The damage frequency did not differ among female, male and vegetative plants in the grazed habitat, where 96% of the plants were grazed. According to the age- and stage-based model, the newest bud generation and the vegetative shoots determine the majority of demographic processes of the plant. Longer-term observations are required to investigate annual fluctuation in bud population dynamics and herbivory levels in order to make predictions about the long-term impact of muskox on bud demography of S. arctica.