Pinus sylvestris sapling growth and recovery from mammalian browsing

Plants employ a range of resistance and tolerance mechanisms to counteract the effects of herbivory and research is still unravelling which strategies are most effective against which herbivores. In commercial forestry, research has focused on understanding the genetic basis of resistance traits and using resistance as a management strategy. However, there has been less focus on addressing the basis and utility of tolerance traits. Scots pine (Pinus sylvestris) is a well-studied forest tree due to its wide distribution, commercial importance and use in forest restoration of degraded lands as an important foundation tree species. Several herbivore species browse Scots pine and, here, we examine the genetic basis of recovery of Scots pine saplings following browsing by red deer (Cervus elaphus) and attempt to describe which plant traits are associated with sapling tolerance. Three hundred saplings from five different open pollinated mothers (five families) were offered to deer in a feeding trial and saplings were left to recover from browsing for one and a half years (two annual growth seasons) in a randomised, replicated common garden. Seven sapling traits were assessed at this time: survival, stem diameter below the leading bud, stem diameter at the base of the sapling, total sapling height, length of the leading bud, average length of three lateral buds, and the total number of lateral buds. Results indicate that browsing of Scots pine by deer influences sapling survival and recovery ability. There were significant family differences in morphological growth traits and these differences were maintained in the presence and absence of browsing. For one recovery trait, length of the leading bud, overcompensation in response to browsing was evident in all families. These data, matched with our finding of no negative relationships between any recovery traits, indicate that Scots pine is quite robust to once-off browsing events by deer. We suggest that at the sapling stage, Scots pine do not employ resistance as a strategy against deer, but tolerate deer browsing to counteract the negative impacts of herbivory. Hence, the use of recovery traits as a management tool to mitigate the negative impacts of browsing is an option worthy of further investigation