A description of the symptoms of Acute Oak Decline in Britain and a comparative review on causes of similar disorders on oak in Europe

Abstract

Acute Oak Decline (AOD) is a relatively new decline-disease affecting both native oak species (Quercus robur and Q. petraea) in Britain. The key aim of this study was to describe the symptoms, and signs of AOD, to set a baseline. The second aim was to compare and review the European literature on what appear to be similar disorders on oak. AOD is characterized by four key features: weeping patches more-or-less vertically aligned on oak tree trunks; cracks between bark plates from which dark fluid seeps; inner bark necrosis and the presence (in .90 per cent of cases) of larval galleries of the oak buprestid, Agrilus biguttatus, on the phloem-sapwood interface. In this study, it was noted that although larval galleries were present in the inner bark in 19 of 21 trees, the 'D-shaped' exit holes of the adult beetles were seen less frequently on bark plates of affected trees (33 per cent of cases). Similar disorders reported in Europe are compared with AOD in Britain and potential causes of the condition discussed. Based on the unmistakable symptoms, it is hypothesized that AOD is a distinctive, identifiable condition within the broader oak decline syndrome.

Acute Oak Decline and Agrilus biguttatus: The Co-Occurrence of Stem Bleeding and D-Shaped Emergence Holes in Great Britain

“…The observed patterns support the theory that emergence holes appear at a later decline stage, after stem bleeds and sometimes in the final years before the death of the host [20]. Over time, galleries and the areas of necrosis in the inner bark [1] are likely to weaken the tree and increase the likelihood of a larvae successfully completing its life cycle. Certainly, the degree of success A. biguttatus can have in the final stages of decline can be dramatic, as highlighted by the emergence of 102 beetles in an eight-week period from a heavily declined tree (that died in the following year).…”

“…Leibl. and Quercus petraea L. [1]. Landowner reports collected between 2006 and 2016 suggest that the condition is widespread across southern and central England, with isolated occurrences in south Wales and along the Welsh borders [2,3].…”

“…Landowner reports collected between 2006 and 2016 suggest that the condition is widespread across southern and central England, with isolated occurrences in south Wales and along the Welsh borders [2,3]. In these regions AOD affects the health of oak species [1,3] that form the largest component of native woodland [4].…”

Impact of climate change on tree-ring growth of Scots pine, common beech and pedunculate oak in northeastern Germany

“…Although the study area is restricted to the northeastern German lowlands, it is likely that the estimated growth trends for Scots pine and common beech can be extended to similar landscapes in central Europe. In the case of pedunculate oak, a general transfer of our results to other regions is not advisable, since this species is currently affected by a complex interplay of biotic and abiotic pathogens, the so called "oak-decline" (Thomas et al 2002, Marçais & Desprez-Loustau 2014, Denman et al 2014). Since our predictions are based on meteorological variables only, the analysis of the impact of other important abiotic or biotic factors potentially affecting the future tree growth may be necessary to obtain a more comprehensive picture of potential future risks on forest vitality due to climate change.…”

Methods for Quantification of the Decline Phenomenon and Determination of the Vulnerability Degree for the Oak Stands in Northwestern Transylvania, Romania

“…These terms are not standardized, being subject to future debates and their definition is still under development. However, it is unanimously accepted that there are two types (models) of decline -an acute one, with fast development, and a chronical one, with slow development in space and time (Denman, 2014). The combination of factors that causes disequilibrium varies on area, year, forest type, leading to a varied symptomatology, which is strongly influenced by the environment and numerous biological interactions (Marcu, 1986;Führer, 1998;Thomas, 2008;Andersson et al, 2011;Santini et al, 2013;Sohar et al, 2013;Dănescu et al, 2015).…”