Exploring for senescence signals in native scots pine (Pinus sylvestris L.) in the Scottish Highlands

The main aim of this project was to explore whether the pine trees in Glen Affric (GAF), one of the more extensive pine woodlands in the northern Scottish Highlands, are, on average, reaching a senescent stage which could ultimately be detrimental to the sustainability of the pine woodland in this region under present management conditions. This aim was realized by (1) comparing the mean stand age of the GAF trees to other pine woodlands around Scotland, (2) exploring whether there was a significant pre-death trend in ring-width series from naturally dead trees and (3) assessing whether a notable change in response of tree growth to climate was noted as a function of age which could indicate that trees were entering a state of senescence.The average age of the GAF pine trees is 236 (±36) years compared to 225 (±55) years for Scotland as a whole and comparing the GAF data to older pine trees around Scotland suggests that the current mature trees should remain healthy for at least the next century. We also note no significant pre-death trend in ring-width time-series measured from recently dead standing trees. Intriguingly, however, there is a consistent weakening in the response of the pine trees to temperatures through the 20th century. Despite younger trees showing, on average, a stronger response to temperatures, they show the greatest temporal instability in response. This response change is likely not related to tree senescence and ongoing research is exploring this phenomenon in more detail.