Effect of ungulates on seedling height growth for common forest species in Wallonia

The adjacent graph shows, for the main Walloon forest species, the change in the average heights of seedlings measured within the sampling units of the Walloon enclosure-exclosure network. The initial heights measured at installation of the device are represented by the horizontal dotted lines while the final heights measured after four years of growth in the enclosures and exclosures are symbolized by the green and red pictures, respectively. These results show that ungulates modify the competitive advantages of the tree seedlings. Beech (Fagus sylvatica) and spruce (Picea abies) are the most frequently observed species. Growth of spruce was not affected by ungulates and growth of beech was reduced by 32%. The growth of hornbeam (Carpinus Betulus), birch (Betula spp.), rowan (Sorbus aucuparia) and oak (Quercus spp.) was proportionally the most reduced by ungulates (from 50% to 100%). Survival probability is related to the height and growth rate of the seedlings. Ungulates strongly affect the growth of the major species present in Wallonia. The growth of spruce and beech that are the most frequent and also climax species is moderately reduced. In contrast, the growth is drastically reduced for less frequent species such as rowan and birch, and also for oak, a species with chronic deficit of regeneration. As a result, ungulates cause substantial difficulties for forest diversification.