Moose and vole browsing patterns in experimentally assembled pure and mixed forest stands

Abstract

Vehviläinen, H. and Koricheva, J. 2006. Moose and vole browsing patterns in experimentally assembled pure and mixed forest stands. Á Ecography 29: 497 Á506.Plants growing in diverse communities are believed to exhibit associational resistance to herbivores, but this hypothesis has seldom been tested experimentally for vertebrate herbivores in forest ecosystems. We examined browsing patterns of the two principal mammalian herbivores of Finnish boreal forests, moose and voles, in young stands where tree species diversity and composition were experimentally manipulated. The stands were composed either of monocultures or different 2 Á5 species mixtures of Norway spruce, Scots pine, Siberian larch, silver birch, and black alder. Voles and moose showed contrasting responses to stand diversity and species composition. In accordance with the predictions of the associational resistance hypothesis, vole damage was higher in tree monocultures than in mixed stands, although stand diversity effects were statistically significant only at one of the three study areas. Voles also damaged more trees in coniferous than in deciduous stands. In contrast, moose browsing tended to increase with the number of tree species in a stand and with the presence of the preferred tree species, birch, in a mixture. The observed differences in vole and moose responses to stand diversity and species composition are likely to be due to different feeding specialisation, foraging patterns, and movement ability of these herbivores. Voles switched to trees only when the supply of a more preferred food (grasses and forbs) was depleted and restricted their feeding choice only to the most palatable tree species regardless of the number of tree species present per stand. In contrast, tree branches and foliage represented an important part of moose diet throughout the year; moose may be able to tolerate secondary plant metabolites of different tree species better than voles and may thus benefit from diet broadening when more tree species are available. Furthermore, the home range size and foraging ability of these two very differently sized herbivores may partly explain the observed differences in utilisation of different tree species. Finally, both moose and voles showed high spatial and temporal variation in their feeding; in particular, vole damage was more influenced by tree species diversity in areas and years with high vole densities. Thus, diversification of forest stands may have very different effects on mammalian browsing depending on the herbivores present, their densities, and the tree species used in reforestation.H. Vehvilä inen (harri.vehvilainen@utu.Herbivores are one of the main factors contributing to the structure of plant communities. The intensity of herbivory experienced by plants is known to be affected by the diversity and species composition of the surrounding vegetation (Tahvanainen and Root 1972, Atsatt and O'Dowd 1976, Pfister and Hay 1988. Many ecological and agricultural studies have documented reduction in herbivory experience...

Effects of bedrock and surficial deposit composition on moose damage in young forest stands in Finnish Lapland

“…Fertile habitats offer moose not only better quality and a larger quantity of food but also a variety of alternative food plants (Niemelä and Danell 1988;Heikkilä 1990;Heikkilä and Härkönen 1993;Månsson 2009;Nikula et al 2008). Pine stands mixed with deciduous seedlings seem to be attractive pastures for moose (Heikkilä 1990;Vehviläinen and Koricheva 2006), especially when birches are overtopping the pine seedlings (Nikula et al 2008). …”

“…food patch, may depend on both the availability of food within the patch and the spatial arrangement of food patches at broader spatial scales, such as an animal's home range. Earlier studies have indicated that resource selection by moose also occurs at several levels of hierarchy in the following order: a landscape (Nikula et al 2004), home range (Cassing et al 2006), food patch and food plant (Berqvist et al 2012;Nikula et al 2008), although it has been suggested that the food selection of moose mainly occurs at the food plant level (Danell et al 1991;Vehviläinen and Koricheva 2006;Berqvist et al 2012). From the point of view of moose damage risk, multi-scale resource selection suggests that underlying factors that affect browsing risk at the plantation or plant level may originate from larger scale processes or factors and should thus be taken into account in the moose damage risk assessment.…”

“…Moose damage risk is mostly affected by the density of the moose population but also many other factors affect the damage risk (Heikkilä and Härkönen 1993). Vulnerability of saplings to moose damage has been studied, for example, in relation to the chemical properties of the plants (Löyttyniemi 1985;Löyttyniemi and Hiltunen 1978;Haukioja et al 1983;Niemelä and Danell 1988), the genetic origin of the seedlings (Haukioja et al 1983), structural characters and species composition of stands (Heikkilä 1990;Heikkilä and Härkönen 1993;Vehviläinen and Koricheva 2006), and in relation to wider structural features of the forest landscape (Heikkilä 1990;Heikkilä and Härkönen 1993;Månsson 2009;Nikula et al 2004Nikula et al , 2008. In addition, habitat fertility has regularly been shown to increase the risk of moose damage (Niemelä and Danell 1988;Heikkilä and Härkönen 1993;Månsson 2009;Nikula et al 2008).…”

The influences of forest stand management on biotic and abiotic risks of damage

“…In their meta-analysis comparing insect herbivory in pure vs. mixed stands, Jactel and Brockerhoff (2007) found twenty-one studies where more palatable host trees were included in the mixture and these mixed stands were more damaged overall than pure stands. The presence of a preferred species (high quality food resource) in a mixed stand increased the level of damage on less preferred species (low-quality food) by mammalian herbivores such as vole and moose (Pusenius et al, 2003;Vehviläinen and Koricheva, 2006). The intensity of Armillaria damage increases with the number of susceptible conifer species in mixed plantations (Gerlach et al, 1997).…”

Scenario analysis of planting density and pre-commercial thinning: will the mixed forest have a chance?

“…However, not only specific preferences but also the surrounding landscape matrix will affect the probability of an individual seedling being browsed (Hornberg 2001;Edenius et al 2002;Bergman et al 2005). Browsing tends to be more intense in mixed species stands and, unsurprisingly, most severe in stands dominated by mixtures of attractive species (Vehviläinen and Koricheva 2006;Milligan and Koricheva 2013).…”