Figure 1.
A conceptual framework for the components influencing affiliate coextinction and community viability during tree epidemics, adapted after Moir et al. [20].
Coextinction and community viability is primarily influenced by host trees, affiliate species, and their interactions. These variables are in turn influenced by several factors (see text). The left photo show an ash dieback diseased tree (classified as dying) surrounded by healthy F. excelsior on Gotland Island in 2009.
Table 1.
Lichen community values and stand characteristics of the 20 wooded study sites on Gotland, Sweden.
Figure 2.
Average proportion of affiliate lichen species projected to go extinct (Se).
(a) Se as a function of the fraction of host trees infected at each study site, given mortality permutations of 2009 levels of dead and dying F. excelsior (unfilled; optimistic scenario) and all infected F. excelsior (filled; likely scenario). Squares represent Se among lichen communities on ash F. excelsior and triangles represent Se among lichen communities on all tree species. (b) Average proportion of affiliate lichen species projected to go extinct (Se) in each management category under the most likely scenario.
Table 2.
Beta regression model results of average coextinction probabilities (Ā).
Figure 3.
Lichen species composition among ash dieback infected host tree populations of F. excelsior.
Average ANOSIM R values for comparison between 20 unaffected pre-epidemic local lichen species composition on F. excelsior tree populations and projected assemblages subjected to optimistic and likely tree mortality perturbations. Data represent average R values of 100 projections for each study site. R-values around 0.5 (above the dashed line) indicate clear differences in species composition between groups.
Figure 4.
Risk curves for seven local lichen communities on F. excelsior subjected to ash dieback.
The curves show the cumulative probability that the proportion of species remaining in the community falls below a certain proportion of the original species following the most optimistic (a) and the most likely scenario (b) of ash dieback mortality. Each curve is computed from 100 replicate communities. Remaining communities fall within the current range, but are not shown to ease visual interpretation.
Figure 5.
Projected average coextinction probabilities (Ā) as a function of host specificity.
(a) Ā for all 174 affiliate lichen species at the most optimistic and the most likely scenarios of ash dieback disease, and (b) for the 23 lichen species currently red-listed in Sweden [21]. Beta regression model results for these relationships are shown in Table 2.