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

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 ..., There is a long history of monitoring at the site with rare longitudinal records from repeated censuses of all trees in ten long thin permanent sample plots, termed “transects”. Hand-drawn maps of the locations of the centre of each individual woody plant ≥1.3 m height in transects I-VI were recorded on a Cartesian coordinate grid by reference to transect edge markers with a regular 30.5-m spacing in 1977. Transects VII-X were similarly mapped in 1984–85. These records were updated and checked for accuracy at each successive enumeration of each transect, including in 2013 before ADB was first observed in the woodland and in anticipation of its arrival. For the present study, these maps were scanned digitally using Esri ArcGIS Pro® 2.7.3 (2021) software onto Ordnance Survey digital maps and allocated their British National Grid coordinate values. The geographical location of the centre of each tree was normalised for slope. After the initial enumeration of each transect, all woody plants..., R, Spatstat, Excel

由子囊菌门真菌白蜡扁盘菌（Hymenoscyphus fraxineus）引发的白蜡枯梢病（Ash Dieback, 简称ADB），其流行病学特征与病害严重程度已被证实与多种立地条件相关，但目前尚缺乏单株树木尺度的相关分析。

本研究在英国一处天然林地保护区的永久样地内，连续两年对约400株欧洲白蜡（Fraxinus excelsior）开展ADB症状分级调查。研究团队依托1945年以来持续维护的完整样地记录，以及1977年以来更新的精细化空间记录，构建了一系列潜在解释变量，涵盖立地环境因子、白蜡树种群密度、林木既往与当前健康状况，以及物种混交度、大小优势度等邻域汇总统计量（Near Neighbourhood Summary Statistics, 简称NNSS）。研究采用广义线性混合效应模型（Generalised Linear Mixed Effects Models, 简称GLMM），检验了上述变量对目标白蜡树ADB病害严重程度的影响。

研究发现，研究区内土壤湿度较高的下坡区域ADB病害严重程度显著更高，而在一处受经营管理的区域病害严重程度最低……

该监测点拥有悠久的历史监测传统，留存有极为稀缺的纵向监测记录：研究人员对10条被称为"样带（transects）"的狭长永久样地内的全部木本植物开展了多次普查。1977年，研究人员以样带边缘间距为30.5米的标记点为参照，在笛卡尔坐标系上绘制了样带I至VI内所有株高≥1.3米的木本植物个体中心位置的手绘地图；1984至1985年，研究人员以相同方式完成了样带VII至X的测绘工作。在每次对各条样带开展普查后，研究人员都会对上述记录进行更新与精度核验，其中包括2013年——即在该林地首次发现ADB疫情之前，为应对疫情可能的入侵所开展的核查工作。

为开展本项研究，研究团队使用Esri ArcGIS Pro® 2.7.3 (2021)软件将手绘地图扫描数字化，匹配至英国地形测量局（Ordnance Survey）的数字地图，并为每个木本植物个体赋予英国国家网格坐标系的坐标值。研究人员针对地形坡度，对每株白蜡树中心的地理位置坐标进行了归一化处理。在完成每条样带的初始普查后，所有木本植物……相关数据均通过R语言、Spatstat包与Excel软件进行处理。