The tree ring growth histories of UK native oaks as a tool for investigating Chronic Oak Decline: An example from the Forest of Dean

Abstract

Declines are a distinctive category of tree disease, complex to define and quantify and challenging \nto mitigate due to their multiple causes and heterogeneous tree response patterns. In many parts \nof Europe oak decline syndromes are severely impacting tree health and having a measurable \neconomic impact on forestry. In the UK the impact of periodic oak declines is expanding against a \nbackdrop of multiple environmental pressures, to levels capable of threatening the UK’s native \noak woodland. Here we explore the growth histories of oak trees at a site symptomatic of Chronic \nOak Decline (COD), in the South of England; Speculation Cannop in the Forest of Dean, \nGloucestershire. The dendrochronological picture at the site reveals that trees with current \nexternal COD symptoms have shown suppressed growth, in relation to the regional average, from \nearly on in their lives. Moreover, there is an amplified reduction in minimum ring width in \nSymptomatic trees as compared to a healthy subsample of Control trees, likely to be heavily \ndominated by reduced latewood width in affected trees, as decline sets in. Broadly, the site \nreveals the initial appearance of decline, roughly 40 years after planting, in 1860. There is \nconsiderable variability in the later decline history pattern in Symptomatic trees but there are \nclusters of decline episodes in the 1920s, 1960s, 1980s and 1990s at this site. The Control trees are \nnot always unaffected but rather show growth releases after each historical decline phase. The \ntrees that currently show external decline symptoms do not have a history of these growth \nreleases. We conclude that investigating the tree ring growth histories at sites impacted by COD \ncould provide an important management tool, and ring width histories of trees at affected sites \nshould be used in the identification of the decline predisposing factors, that a management \nstrategy requires