LAND: Ecological dynamics by wild ungulate grazing

Our project aimed at contributing to increase the knowledge on the ecological role of deer in boreal forest. We expected less plant species with increasing herbivory intensity, but found the opposite. At Svanøy, the West coast of Norway, we found a positive effect of high densities of red deer on plant species richness. Our analyses, both observations and experiments, represent a potent mix for trustworthy conclusions within ecological research. With the help of powerful statistical methods we found that only at very high intensities of herbivory, within a forest area with farmed red deer, there was a negative effect of the deer herbivory. It is important to dig deeper into the results to know more on how the deer affects the forest systems. At Svanøy it was very clear that tree species like rowan and dwarf shrubs like heather and lingonberry were losers. This is the typical winter food for red deer. The winners were the species rich groups of flowering plants and bryophytes. There was a distinct relationship between losers and winners. Less trees and shrubs meant more space and light for the low-growing species. The influence of red deer as a winter browser changed the competitive conditions in the forest. One woody species surprisingly contrasted this general finding: the very abundant and ecological important species bilberry (Vaccinium myrtillus) did much better than the other woody species and were abundant up to intermediate levels of herbivory, although its biomass and reproduction was clearly reduced by deer herbivory. The temporal changes that the red deer impose on the forest systems are very important in nature management. PhD-candidate Marte Lilleeng at the Western Norway University of Applied Sciences investigated data back to 2001 and found that red deer increases the turnover in plant species. It appears that forest full of deer will consist of less recruiting trees and more low-growing species which confirms our other findings. In the big picture there is a tendency for browsed forest to get plant communities that are more homogenous across the forest areas. However, we also investigated effects of browsing on beetle communities and these tended to be more heterogenous across our study sites in the old-growth forest of Svanøy. We found a improved way to induce defence responses in wild populations than the traditional clipping studies that ecologist often perform.Instead we sprayed plants with methyljasmonate. Plants responded with reduced growth and was less attractive to insect herbivores. Our experiments show that the induction of these defense responses are costly for the plants that often reduce their growth and reproduction. The bilberry plant can even communicate the need for defense to their neighbours so that other plants know they are attacked. The studies of PhD-student Rafael Benevenuto shows that the defense responses are coupled with upregulation of ca 3500 genes and downregulation of ca. 1500. However, although we managed to induce defence responses in bilberry both summer and winter through chemical treatment, we could not find an isolated effect of deer herbivory that caused the same defence response in deer browsed plants. It may be that deer browsing that largely appers in winter is not a strong enough signal for the plant to produce anti-browsing substances, or it may be that this part of the plant?s immune system is mainly targeted to deter insects, with less complex digestion system that ungulates, from eating the plant. Many other animals than large mammals also feed on bilberry. Insects, for example geometrid larvae, often has bilberry and other shrubs as their most important food plants. Studies performed by Marte Lilleeng showed that there are less larvae in browsed than unbrowsed forest most probably because the bilberry plants gets smaller. There is probably a direct competition effect among the large herbivore, red deer, and the smaller herbivores, the insects, in this case. In addition, it appears that there is an additional effect on the plant quality. Interestingly, plants that have experienced some deer browsing appear to be more palatable both to insects and deer. In total, our studies in this project shows that red deer plays an important ecological role in the ecosystemet we have studied. Red deer is structuring the pine-bilberry forest and defines what plants that may grow, reduces the amount of dominant species of trees and shrubs, and increases the amount of flowering plants and bryophytes. In sum the biodiversity increases with deer browsing, but plant communities may homogenise whereas insect communities may heterogenise. Earlier research often focus on the damage that deer causes, whereas we have focused on the ecological role. Our research shows that the level of browsing found in this forest are not detrimental for biodiversity but that it may cause winners and losers.

Today, red deer is the most abundant large wild grazing herbivore in Norway, but we do not know how important the grazing factor it is for the development of patterns and processes in Norwegian landscapes. Nature conservationists have raised concerns that the growing deer population may harm biodiversity and ecological processes. Such knowledge require long-term studies on ecological dynamics that are generally not feasible within regular research project funding. Large efforts and investments have alre ady been made in experimental design and data collection which will benefit the current project. Twelve sites were established in 2001 across the island Svanøy. The experiments were created by establishing a grazing exclosure and an ungulate grazed contro l area (100m2) per site. We have also estimated a gradient in grazing intensity by monitoring the presence of pellet groups. This gradient approach adds the possibility to connect grazing effects to indirect density measures of deer that cannot be attaine d by experimental data alone. Detailed sampling of vegetation has been performed in permanent plots since 2001. Information on dynamics of all forest layers, as well as key plant species will have time series of 10 years in 2011. The combination of an e xperimental study design and a gradient approach is one of the primary strengths of this proposal. In addition we have planned new data recordings prepared together with top national and international scientists, which will broaden the generated knowled ge to indirect effects of deer grazing. This will include analysis of population dynamics of a dominant and ecological important plant species in relation to grazing and resources and indirect effects on the invertebrate community by a network approach an d by testing edibility of important food plants. Moreover, we have designed a special research module to deal with the transfer of knowledge from science to wildlife managers, a prime motivation for this project.