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Landscape epidemiology of ash dieback

Citation

Grosdidier, Marie; Scordia, Thomas; Ioos, Renaud; Marçais, Benoit (2020), Landscape epidemiology of ash dieback, Dryad, Dataset, https://doi.org/10.5061/dryad.ns1rn8ppc

Abstract

1. 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. 2. 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. 3. 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. 4. 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.

Methods

Data was collected by ground survey during a period of 7 years on a network of plots located on a systematic grid design

Plot were established on grid node with ash (100-111 depending on the year)

Data were collected

- Ash basal area: measure of ash tree circumference on plots with fix surface (128, 800 and 1250 m² depending on their diameter at breast height)
  sum of tree basal area weighted by the surface of the plot on which they were measured
  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.
  The polygon  is derived from the tree cover IGN shape file VEGETATION.shp (http://professionnels.ign.fr).
   rPA100 is the perimeter/area ratio for that polygon

- Ash heath status: visual assessment of crown condition and of collar canker presence

- Hymenoscyphus fraxineus presenc: qPCR test in laboratory on samples taken from the field

- Amount of H. fraxineus infected ash rachides in the litter: collection of ash rachides on fix surface transect, visual assessment of their infection level
   measure of either their total length or weight after 24h at 50°C per infection category (infected / not infected)

- Fructification of H. fraxineus: collection of infected ash rachides on fix surface transect, counts of apothecia in the laboratory, measure of total infected rachis length

- Data on microclimatein crown of ash trees (temperature, relative humidity)
   EL-USB-2 data loggers (Lascar Electronics Ltd UK, Wiltshire, United Kingdom)

 

Usage Notes

Information in the uploaded readme.csv file