3. RESULTS
3.1. The lichen flora of Estonian forests
3.1.1. Composition, species richness and substrata of forest lichens A total of 481 species of forest lichens were confirmed to inhabit Estonia.
Additional 118 species inhabit substrata that occur in forests, but have not been confirmed there so far. Thus, the probable number of forest lichens reached 599 species (I).
Frequency estimates were computed for 70% of confirmed forest lichen species. The eight most frequent species were present in all but 1–2 studies (e.g.
Hypogymnia physodes, Parmelia sulcata, Chaenotheca ferruginea), whereas 154 species (47%; mainly microlichens) occurred in only 1–2 studies. Among the studies with at least 10 species lists presented, the mean relative frequency exceeded 10% for 68 species, while it was below 5% for more than half (215) of the species considered. Ninety of these latter species have been classified as rather to very rare, and 83 species frequent to very frequent in Estonia (sensu Randlane and Saag 1999). However, some species with low average frequencies were locally quite common. For example, the macrolichen Cetraria islandica occurred on average in 8.4% of species lists, but it was present in 75% of the lists of one study.
Calicioid, cetrarioid, cladonioid, parmelioid, pendulous, sorediate crustose and lichenicolous and parasitic species totalled 46% of the forest lichen species, while some species rich genera (e.g. Verrucaria) were represented with only one species or were absent (Table 4 in I).
According to the species composition, there were five broad substratum types for the Estonian forest lichens – broad-leaved trees, common deciduous and coniferous trees, branches and undergrowth, windthrows, and other ground-level substrata (Fig. 2). The highest numbers of all and of unique species were recorded on living trees (I), particularly on aspen (IV). Ground and CWD (e.g.
snags with exposed wood, II) were also found to host relatively high number of species, despite the low number of studies about these substrata.
Although the general species composition and substrata of forest lichens were assessed as relatively well known, groups with unclear taxonomy or difficult field identification are still insufficiently studied. For example, the occurrence of Lepraria incana and other highly similar Lepraria species differed significantly between substrata (χ2-test: P < 0.01) (III).
0.0 0.2 0.4 0.6 0.8 1.0 1.2 Euclidean distance
Windthrows Logs of other deciduous treesPopulus tremulaPinus sylvestrisAlnus glutinosaPicea abiesPicea abiesJuniperus communisBetula sp.Populus tremulaFraxinus excelsiorAcer platanoidesSorbus acupariaPopulus tremulaAlnus glutinosaPinus sylvestrisQuercus roburOther bushesUlmus glabraAlnus incanaSalix capreaTilia cordataPicea abiesSnag wood snag bark snag bark branches snag bark snag bark snag barkBetula sp.StumpsGround log
Broad-leaved trees
Common deciduous and coniferous trees
Ground-level substrata Branches and undergrowth
Figure 2. Similarity of lichen composition of different substrata in Estonian forests according to cluster analysis (Ward's method; I).
3.1.2. Lichen flora of snags
The lichen flora of snags without bark (S2) was distinct from that of snags with bark (S1) and live trees (Fig. 3 in II). Tree species influenced the number, total coverage and diversity of lichens on live trees and S1, but not on S2; a similar pattern emerged in substratum acidity (Fig. 3). The highest total numbers of lichen species per 100 trunks were estimated for S2 of birch, black alder and Norway spruce (Table 4 in II), which were relatively species poor substrata at the single trunk scale. Indeed, the average number of lichen species per trunk and the estimated total number of species of the twelve studied substrata were not significantly correlated (rs = 0.32, P = 0.31). S2 had 15 unique species (ten of them calicioid species), while S1 had only three. In general, the species that were unique to snags made up 25% of the lichen species on the studied trunks (II). The estimates of relative species richness of different substrata were not influenced if leprarioid crusts were re-analysed and identified as six different species of Lepraria (III).
3.5 4 4.5 5
L1 L2 S1 S2
Tree type
pH
Pinus Picea
Alnus Betula
Figure 3. Acidity (pH) of bark and wood of different tree species and tree types (S1 = snag with bark, S2 = decorticate snag; L1 and L2 = live trees near S1 and S2, respectively). Live Pinus and Picea differed significantly from live Betula and Alnus, and S1 of Pinus from S1 of the other species (U-tests: P < 0.001).
3.1.3. Comparative vitality and diversity of lichens and bryophytes on retention trees
We explored general and species-specific vitality of lichens and bryophytes on live retention trees and adjacent forest tree trunks. The damages on retention trees were severe and independent of tree species for bryophytes throughout cuts (Fig. 3 in IV), but weak for lichens, particularly at the edge of clear-cut, and on aspen and ash (Fig. 2 in IV). On average, 2% of lichen thalli, but 60% of bryophyte shoots became damaged in two years.
The retention trees and adjacent forest trees hosted similar total numbers of cryptogam species and mean numbers of lichen species per trunk. However, the average decrease of 1.1 bryophyte species per trunk on retention trees, compared with the forest trunks, was highly significant (paired t-test:
P < 0.001).
Relationships between the average damage scores of the same species on retention trees and forests trees were different for lichens and bryophytes (Fig. 4). For lichens, the damages were mostly explained by the general sensi-tivity of certain species. Crustose lichens (e.g. Loxospora elatina, Megalaria grossa, Ropalospora viridis) and some macrolichens with small foliose or podetial thalli (e.g. Cladonia coniocraea, Vulpicida pinastri) were in remarkably good condition. For bryophytes, the damages in clear-cuts greatly exceeded those in forests, particularly for the species that were relatively vital in forests (e.g. Homalia trichomanoides).
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Average damage (forest)
Average damage (clear-cut)
2 2
2
10
Figure 4. Linear regressions between the average damage scores on forest and retention trees of 19 bryophyte (circle dots, discontinuous line) and 24 lichen species (filled dots, solid line). For lichens: Pintercept = 0.11, Pslope < 0.001, R2 = 0.53. For bryophytes:
Pintercept < 0.001, Pslope = 0.27, R2 = 0.07. Numeric labels indicate the number of species with similar values.