Can browsing by deer in winter induce defence responses in bilberry (Vaccinium myrtillus)

Wild ungulates are key determinants in shaping boreal plant communities, and may also affect ecosystem function through inducing the plant defence systems of key plant species. We examined whether winter browsing by deer could increase the resistance of bilberry (Vaccinium myrtillus). We used three indicators of induced bilberry defence: reduced growth (a), reduced reproduction (b) and decreased insect herbivory (c) in focal plants. In a field experiment, using a randomised block design, we exposed half of plants twice in winter to exogenously applied methyl jasmonate (MeJA) and crossed this factor with randomly selecting browsed and unbrowsed plants. We predicted that MeJA-plants would have significant lower growth, reproduction and insect herbivory than Control plants. We also expected that Browsed plants would experience similar negative effects and that there would be an interaction between MeJa and Browsed indicating a possible additive effect. Growth, flowering and insect herbivory were significantly lower in MeJA than in Control, as expected. We did not find the same reduction for Browsed and no significant interaction between factors. The combined treatment, unexpectedly, flowered more and showed higher levels of insect herbivory than MeJA. Our study showed that defence responses of bilberry may be induced by exogenously-applied MeJA in winter. Our study could not confirm whether winter browsing by deer can induce the same defence responses.