Lichen community values and stand characteristics of the 20 wooded study sites on Gotland, Sweden.

<p>Site-level pre-epidemic lichen community values from inventories in 1989–1991; showing the number of <i>Fraxinus excelsior</i> trees inventoried for lichens, species richness (S.R.) and abundance values (No. of Ind.) of all lichens and red-listed species, respectively. Stand characteristics for each site and management category; showing stand size (ha), percentage values of canopy closure, fraction of <i>F. excelsior</i> population with signs of recent pollarding (pollarded within the last two decades), and percentage tree species composition. Projected post-epidemic site-level lichen community values; showing the percentage of the <i>F. excelsior</i> population classified as dead or dying (optimistic scenario) and infected (likely scenario), average ANOSIM R values comparing pre-epidemic and projected post-epidemic local lichen species composition on <i>F. excelsior</i> tree populations, the projected probability values of no local coextinctions (Res) and the average percentage of extinct species (<i>S_e</i> ) among <i>F. excelsior</i> tree populations and all tree species in the respective post-epidemic community.</p>*<p>bonferroni-corrected <i>p</i><0.05, ** b.f. <i>p</i><0.001 ¹the probability of no coextinctions and ²the average proportion (%) of extinct species (<i>S_e</i>) on ash <i>F. excelsior</i> in the post-epidemic community ³the probability of no coextinctions and ⁴the average proportion (%) of extinct species (<i>S_e</i>) when including occurrences on all tree species.</p

Average proportion of affiliate lichen species projected to go extinct (<i>S_e</i>).

<p>(a) <i>S_e</i> as a function of the fraction of host trees infected at each study site, given mortality permutations of 2009 levels of dead and dying <i>F. excelsior</i> (unfilled; optimistic scenario) and all infected <i>F. excelsior</i> (filled; likely scenario). Squares represent <i>S_e</i> among lichen communities on ash <i>F. excelsior</i> and triangles represent <i>S_e</i> among lichen communities on all tree species. (b) Average proportion of affiliate lichen species projected to go extinct (<i>S_e</i>) in each management category under the most likely scenario.</p

Lichen species composition among ash dieback infected host tree populations of <i>F. excelsior</i>.

<p>Average ANOSIM R values for comparison between 20 unaffected pre-epidemic local lichen species composition on <i>F. excelsior</i> 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.</p

Risk curves for seven local lichen communities on <i>F. excelsior</i> subjected to ash dieback.

<p>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.</p

Projected average coextinction probabilities (<i>Ā</i>) as a function of host specificity.

<p>(a) <i>Ā</i> 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 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045701#pone.0045701-Grdenfors1" target="_blank">[21]</a>. Beta regression model results for these relationships are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045701#pone-0045701-t002" target="_blank">Table 2</a>.</p

Beta regression model results of average coextinction probabilities (<i>Ā)</i>.

<p>Beta regression models explaining average coextinction probabilities (<i>Ā)</i> of 174 lichen species occurring on trees (all tree species included) in 20 wooded stands affected by ash dieback disease, under the most optimistic scenario and the most likely scenario of <i>F. excelsior</i> tree death. Beta regression explaining average site-level proportions of extinct lichen species (<i>S_e</i>) on all trees in relation to site management category.</p

A conceptual framework for the components influencing affiliate coextinction and community viability during tree epidemics, adapted after Moir <i>et al.</i>[20].

<p>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 <i>F. excelsior</i> on Gotland Island in 2009.</p

Occurrence Patterns of Lichens on Stumps in Young Managed Forests

<div><p>The increasing demand for forest-derived bio-fuel may decrease the amount of dead wood and hence also the amount of available substrate for saproxylic ( = dead-wood dependent) organisms. Cut stumps constitute a large portion of dead wood in managed boreal forests. The lichen flora of such stumps has received little interest. Therefore, we investigated which lichens that occur on stumps in young (4–19 years), managed forests and analyzed how species richness and occurrence of individual species were related to stump and stand characteristics. We performed lichen inventories of 576 Norway spruce stumps in 48 forest stands in two study areas in Central Sweden, recording in total 77 lichen species. Of these, 14 were obligately lignicolous, while the remaining were generalists that also grow on bark, soil or rocks. We tested the effect of characteristics reflecting successional stage, microclimate, substrate patch size, and the species pool in the surrounding area on (1) total lichen species richness, (2) species richness of obligately lignicolous lichens and (3) the occurrence of four obligately lignicolous lichen species. The most important variables were stump age, with more species on old stumps, and study area, with similar total species richness but differences in occupancy for individual species. Responses for total lichen species richness and species richness of obligately lignicolous lichens were overall similar, indicating similar ecological requirements of these two groups. Our results indicate that species richness measurements serve as poor proxies for the responses of individual, obligately lignicolous lichen species.</p></div

Sample based rarefaction curves comparing species density between young and old stumps (on young and old clear-cuts, respectively) at Finspång and Fredriksberg.

<p>In each stand, 12 stumps were surveyed. The 95% confidence limits have been excluded for clarity, but did not overlap between young and old stumps.</p

Relative importance of stand-level explanatory variables (RVI) for total lichen species richness, obligately lignicolous species richness and occupancy of three obligately lignicolous lichen species on Norway spruce stumps in 48 young managed forest stands.

<p>Relative importance of stand-level explanatory variables (RVI) for total lichen species richness, obligately lignicolous species richness and occupancy of three obligately lignicolous lichen species on Norway spruce stumps in 48 young managed forest stands.</p