Plant-herbivore interactions in montane willow communities
This project investigated the impacts of browsing by large herbivores on all aspects of the life cycle of montane willows, using Salix arbuscula L. (Mountain Willow) as the main model species. S. arbuscula was found to be almost entirely insect pollinated, although the levels of wind pollination varied between populations. The density of nearby male plants had a positive effect on fruit set in both insect and wind pollinated catkins, but the effect was stronger in wind-only pollinated catkins. In insect pollinated catkins, catkin characteristics such as length and total number of flowers were most important in determining fruit set. Browsing was found to have both direct and indirect negative impacts on seed production in S. arbuscula, which was also highly variable between years. Direct effects included reduction of the number of inflorescences produced by browsing removal of the previous year's growth, on which most inflorescences are found. There were fewer inflorescences found per shoot on browsed plants, suggesting that browsing also reduces inflorescence production via resource limitation. Lower numbers of inflorescences per plant led to fewer pollinator visits and resulted in reduced seed production, particularly in years of poor overall production. Seed and early seedling survival were found to be strongly limited by microsite availability, as both S. arbuscula and S. lapponum required bare ground for germination and early survival. Slugs were found to have a negative impact on seedlings during the first season of growth, where as small mammals (bank voles) had a negative effect one the seedlings were larger. Growing in disturbed microsites may also favour seedling establishment through reducing the likelihood of slug and small mammal predation.