The response of Vaccinium myrtillus to variations in grazing intensity in a Scandinavian pine forest on the island of Svanøy

Abstract

The impact on the performance of dwarf shrub Vaccinium myrtillus L. (bilberry) subjected to differing natural intensities of grazing by Cervus elaphus L. (red deer) was examined in a mature Scandinavian pine forest, on Svanøy, an island on the western coast of Norway. All the study sites were in forest where bilberry dominated the forest floor and no forestry activities had been carried out for several decades. Pellet group counts were used as measure of grazing intensity. Bilberry size, abundance, and fruit set, and invertebrate activity on bilberry were negatively related to grazing intensity. The responses varied between early and late summer (negative or neutral), but impact on plant size was negative throughout the season. Because of the large variation in grazing intensity represented in our study, we can, in contrast to many experimental studies, show that grazing affects the performance of bilberry even at low grazing intensities. The effect on fruit production and invertebrate activity on bilberry indicates that red deer grazing has a negative impact on the population dynamics of the plant and invertebrate herbivores.

Differential effects of herbivory and pathogen infestation on plant population dynamics

“…In studies showing strong effects of deer on plant or population performance damage intensities were generally higher (Knight 2004;McGraw and Furedi 2005). Plant and population performance commonly decrease with increasing deer grazing intensity (Russell et al 2001;Hegland et al 2005;Knight et al 2009;Hegland et al 2010). Hegland et al (2010) found for Vaccinium myrtillus that population growth rates were reduced at relatively high grazing intensities, while k was greater or close to 1.0 at lower intensities (which corresponded to a grazing pressure of 5-10% of the annual shoots).…”

Effect of fertilization, tiller cutting and environment on plant growth and yield of European blueberry (Vaccinium myrtillus L.) in Norwegian forest fields

“…Another reason could be caused by alternate bearing resulting in a strong yield reduction after the high yield in 2009 [21,22]. It is also shown that after a high yielding year, plants were more suited to browsing because of changes in chemical composition of shoots and leaves, and browsing would have effect on yield [14,28,45]. In 2010 there was one fruit per five short shoots at F3, while fruits were absent in F4 (Table 8).…”

“…Our data do not explain the reason of the difference between the fields in 2010. However, the results of 2011 could be explained by the relatively short LS growth of F4 caused by spring browsing [14,33]. Short LS-growth gave fewer nodes and thereby fewer Nodes/LS at F4 than at F3.…”

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

“…Bilberry is considered a key species in these systems and plays an important ecological role as food source for many invertebrate pollinators and herbivores, birds and small and large mammals, which benefit from its early flowering in spring, deciduous leaves in summer, rich berry production in autumn and evergreen stems in winter (Jacquemart 1993;Welch et al 1997;Sela˚s 2000Sela˚s , 2001Hja¨lte´n et al 2004;Wegge et al 2005). Forest-dwelling ungulates such as red deer (Cervus elaphus) and moose (Alces alces) feed on bilberry, particularly in winter when other food sources may be scarce (Hjeljord et al 1990;Hegland et al 2005). Several studies by Sela˚s and colleagues (Sela˚s 1997(Sela˚s , 2000(Sela˚s , 2006Sela˚s et al 2013) have, for example, shown close correlations among bilberry production and population sizes of both invertebrate and vertebrates herbivores known to feed on bilberry.…”