Neighbourhood effects on the risk of an unpalatable plant being grazed

Most studies on the importance of the neighbourhood on a plant's risk ofherbivory have focused on palatable plants and how they are protected byunpalatable neighbours. This study examined the grazing intensity of arelatively unpalatable shrub, Buxus sempervirens, indifferent neighbours. Exactly 2683 plants of Buxussempervirens (including 172 controls) were sampled in 12 enclosedpastures belonging to 4 sheep farms. The enclosures were grazed at 3 differentseasons (spring, summer and autumn). Plants were divided in 4 age/hight classes(first year, < 4 cm, 4–10 cm, 10–40cm) and into 8 neighbourhoods. The first of these wascharacterisedby the absence of any plants within a radius of 5 cm around theBuxus individual and the 7 others by the identity of thedominant species in contact with the Buxus plant. Theintensity of grazing on the neighbouring plants were also recorded. At the endof one year's monitoring, 26.2% of Buxus sempervirensplants had been grazed. The proportion of plants grazed was significantlyhigherin spring than in the other two seasons. It decreased with increasing plantage.It was higher in neighbourhoods that were intensively grazed than in those withlight grazing. The proportion grazed in the absence of a neighbour plant wasintermediate between the previous two. The probability of a plant of aninvadingspecies being grazed is influenced by factors other than its life-historytraits. Some neighbourhoods consisting of unpalatable plants facilitate theestablishment of Buxus sempervirens by protecting theyoungplants from grazing, whereas other highly palatable neighbourhoods are readilygrazed by sheep, thus indirectly increasing the proportion of Buxussempervirens that are grazed. The young and short (< 4cm in height) Buxus plants, which are lessrecognisable by sheep, are most sensitive to the impact of grazing.