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A dendrochronological approach to the study of Chronic Oak Decline in the Forest of Dean / NEIL MATTHEWS
Swansea University Author: NEIL MATTHEWS
DOI (Published version): 10.23889/SUThesis.69249
Abstract
Chronic Oak Decline (COD) is a disease complex with multiple biotic and abiotic causal factors. UK natural oak woodland has a long history of recurrent oak decline outbreaks, however, an increase inseverity and frequency of decline, along with the spread of an acute complex, combine to pose a signif...
| Published: |
Swansea University, Wales, UK
2025
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | Ph.D |
| Supervisor: | Gagen, M. H. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa69249 |
| Abstract: |
Chronic Oak Decline (COD) is a disease complex with multiple biotic and abiotic causal factors. UK natural oak woodland has a long history of recurrent oak decline outbreaks, however, an increase inseverity and frequency of decline, along with the spread of an acute complex, combine to pose a significant threat to oak in the UK. This thesis hypothesises that, as COD outbreaks are periodic, tree ring histories in currently symptomatic and healthy trees would give insight into the disease complex. Two cohorts of Quercus robur L. (control and symptomatic) found in plantations of two differing ages at sites in the Forest of Dean were sampled for ring width and stable isotope dendrochronology. Speculation Cannop (SC), is a plantation of Napoleonic aged oak established from 1811 to supply the Royal Navy dockyards with timber. Chestnuts Wood (CW) was established in the 1950’s on an ancient woodland site. A novel method of crown classification assessed tree health in the studied cohorts. Tree ring widths were measured and cross dated using standard methodologies to construct chronologies for the two cohorts at both sites. Basal Area Increment (BAI) was also calculated to consider age related trends. A statistical Change Point Test was devised for determining step changes in tree ring growth that might be past points of decline in the tree ring records. Stable carbon and oxygen isotope analysis was carried out on a subsample of trees at each site. Event years were determined from pointer year analysis and a modified Abrupt Growth Change method and growth (via BAI) compared pre and post event year. Carbon and oxygen isotope ratios were likewise compared across event years. Significant differences in ring width, growth parameters height and diameter at breast height (DBH), and carbon isotope series were observed between the control and symptomatic cohorts at both sites. The summer source water signal, known todominate variability in UK oak stable isotope time series, masked any conclusive decline history in the stable oxygen isotope series. Insect defoliation events were inferred from the ring width series and the effect of successive episodes discussed in relation to development of decline at both sites. Dendrochronological histories can give useful insight into past decline episodes to aid understanding of how different trees are likely to respond to current and future outbreaks. |
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| Item Description: |
A selection of content is redacted or is partially redacted from this thesis to protect sensitive and personal information |
| Keywords: |
Dendrochronology, Chronic Oak Decline, Quercus robur |
| College: |
Faculty of Science and Engineering |
| Funders: |
Woodland Heritage |