DOI: 10.5061/dryad.ns1rn8ppc
title: Landscape epidemiology of ash dieback

description: Ash dieback is induced by Hymenoscyphus fraxineus, an invasive pathogenic
 fungus. It is causing severe damage to European ash populations. However,
 the local environment, such as climate or site conditions, is known to
 affects ash dieback. We studied the landscape epidemiology of the disease
 on a 22 km² area in north-eastern France at two stages of the invasion
 process using Bayesian spatio-temporal models fitted with integrated
 nested Laplace approximation (INLA). Several features characterizing
 disease severity, crown dieback, frequency of collar canker, and density
 of infected leaf debris in the litter were determined on a regular grid
 over a 3.5 x 6.5 km area. We first analysed the effect of landscape
 features on the disease establishment stage in 2012, two years after the
 first report of the disease in the area, and then on further disease
 development, in 2016–2018. Landscape features had little impact on the
 disease at the establishment stage but strongly determined its further
 development. Local fragmentation of tree cover was the most important
 factor, with trees that are isolated or in hedges far less affected than
 trees in a forest environment. We showed that they were subjected to
 different microclimates, with higher crown temperatures unfavourable to
 pathogen development. Low host density strongly reduced disease
 development. The presence of large ash populations in the vicinity
 affected local disease severity up to several hundred meters. Synthesis.
 We showed that the landscape characteristics strongly affect the
 development and spread of ash dieback. The disease is far less severe in
 forest conditions when ash density is low or in open canopies such as
 hedges and isolated trees. Ash trees are often in these types of
 landscapes, which should strongly limit the overall impact of Ash dieback.
description: Data was collected by ground survey during a period of 7 years on
 a network of plots located on a systematic grid design.
 Plots were established on grid nodes with ash (100–111 depending
 on the year). Data were collected: -
 Ash basal area: measure of ash tree circumference on plots with fixed
 surface (128, 800 and 1250 m² depending on their diameter at breast
 height)<br>  sum of tree basal area weighted by the surface of the
 plot on which they were measured<br>  This was used to compute the
 Ash density in the neighbourhood (HAN, host abundance in the
 neighbourhood) - rPA100 is a tree cover fragmentation
 index computed from a polygon of tree cover within 100 m from plot
 center.<br>  The polygon is derived from the tree cover IGN shape
 file VEGETATION.shp (http://professionnels.ign.fr).<br>   rPA100 is the perimeter/area ratio for that polygon - Ash health status: visual assessment of crown condition and of collar canker presence - <em>Hymenoscyphus</em> <em>fraxineus</em> presence: qPCR test in laboratory on samples taken from the field - Amount of <em>H</em>. <em>fraxineus</em> infected ash rachides in the litter: collection of ash rachides on fix surface transect, visual assessment of their infection level<br>   measure of either their total length or weight after 24h at 50°C per infection category (infected / not infected) - Fructification of <em>H</em>. <em>fraxineus</em>: collection of infected ash rachides on fix surface transect, counts of apothecia in the laboratory, measure of total infected rachis length - Data on microclimate in crown of ash trees (temperature, relative humidity)<br>   EL-USB-2 data loggers (Lascar Electronics Ltd UK, Wiltshire, United Kingdom)
description: Information in the uploaded readme.csv file.