Neighbours matter and the weak succumb: Ash dieback infection is more severe in ash trees with fewer conspecific neighbours and lower prior growth rate

• Published in: The Journal of ecology Vol. 111; no. 10; pp. 2118 - 2133
• Main Authors: Cracknell, David J., Peterken, George F., Pommerening, Arne, Lawrence, Peter J., Healey, John R.
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.10.2023
• Subjects: conspecificity; Dieback; disease progression; Epidemiology; Forest Science; Fraxinus excelsior; Fungi; Growth rate; Hymenoscyphus fraxineus; Records; Signs and symptoms; Skogsvetenskap; Statistical analysis; statistics; Symptoms; Synthesis; Thinning; tree and stand measurements; Trees; vigor; Woodlands
• ISSN: 0022-0477; 1365-2745; 1365-2745
• DOI: 10.1111/1365-2745.14191

The epidemiology and severity of ash dieback (ADB), the disease caused by the ascomycete fungus Hymenoscyphus fraxineus , has been linked to a variety of site conditions; however, there has been a lack of analysis at an individual tree scale. Symptoms of ADB were scored on ca. 400 trees of Fraxinus excelsior (ash) in permanent sample plots during two successive years in a UK natural woodland reserve. Using comprehensive plot records maintained since 1945, and detailed spatial records updated since 1977, we assembled an array of potential explanatory variables, including site environment factors, ash tree density, previous and present tree condition and near neighbourhood summary statistics (NNSS), such as species mingling and size dominance. Their impact on the severity of ADB of focal ash trees was tested with generalised linear mixed effects models (GLMM). The severity of ADB was much greater in the lower slope parts of the site with moister soils and least in a managed area subject to tree thinning in the previous 35 years. Severity of ADB had a negative association with focal ash tree prior relative growth rate over a period of a decade immediately before the disease was detected at the site. Greater ADB severity was also significantly associated with smaller diameter at breast height of ash trees. Additionally, ADB was significantly positively associated with a greater proportion of heterospecific trees amongst the six nearest neighbours of the focal tree. Synthesis. The relationship of the severity of ADB disease with site environment, tree condition and neighbourhood is complex but nevertheless important in the progression of the disease. The findings suggest some silvicultural interventions, such as thinning to increase the vigour of retained ash trees, might reduce the impact of ADB. Mae epidemioleg a difrifoldeb lladdwr yr ynn (ash dieback), y clefyd a achosir gan y ffwng ascomycet Hymenoscyphus fraxineus , wedi ei gysylltu ag amrywiaeth o amodau safle, ond bu diffyg dadansoddi ar raddfa coed unigol. Sgoriwyd symptomau lladdwr yr ynn ar oddeutu 400 o goed Fraxinus excelsior (ynn) mewn lleiniau sampl parhaol yn ystod dwy flynedd yn olynol mewn gwarchodfa coetir naturiol yn y Deyrnas Unedig. Gan ddefnyddio cofnodion lleiniau cynhwysfawr a gadwyd ers 1945, a chofnodion gofodol manwl a ddiweddarwyd ers 1977, casglwyd amrywiaeth o newidynnau esboniadol posib, gan gynnwys ffactorau’n ymwneud ag amgylchedd y safle, dwysedd coed ynn, cyflwr coed blaenorol a phresennol ac ystadegau cryno cymdogaethau cyfagos (NNSS), megis cymysgu rhywogaethau a goruchafiaeth maint. Profwyd eu heffaith ar ddifrifoldeb lladdwr yr ynn gyda modelau effeithiau cymysg llinol cyffredinol. Roedd difrifoldeb lladdwr yr ynn ar ei fwyaf ar lethrau is y safle gyda phriddoedd mwy llaith ac ar ei leiaf mewn ardal reoledig a oedd wedi bod trwy broses deneuo coed yn y 35 mlynedd flaenorol. Roedd gan ddifrifoldeb lladdwr yr ynn gysylltiad negyddol â chyfradd twf cymharol coed ynn dros gyfnod o ddegawd yn union cyn i'r clefyd gael ei ganfod ar y safle. Roedd graddfa ddifrifoldeb lladdwr yr ynn hefyd yn gysylltiedig â diamedr llai ar uchder coed ynn. Roedd gan laddwr yr ynn hefyd gysylltiad cadarnhaol iawn â chyfran uwch o goed hetero‐benodol ymhlith chwe chymydog agosaf y goeden dan sylw. Synthesis. Mae'r berthynas rhwng difrifoldeb clefyd lladdwr yr ynn ag amgylchedd y safle, cyflwr y coed a’r gymdogaeth yn gymhleth ond serch hynny'n bwysig yn natblygiad y clefyd. Mae'r canfyddiadau’n awgrymu y gallai rhai ymyriadau coedamaeth, megis teneuo i gynyddu egni’r coed ynn sydd ar ôl, leihau effaith lladdwr yr ynn.