Using lichen communities as indicators of forest stand age and conservation value

Evaluating the conservation value of ecological communities is critical for forest management but can be challenging because it is difficult to survey all taxonomic groups of conservation concern. Lichens have long been used as indicators of late successional habitats with particularly high conservation value because lichens are ubiquitous, sensitive to fine-scale environmental variation, and some species require old substrates. However, the efficacy of such lichen indicator systems has rarely been tested beyond narrow geographic areas, and their reliability has not been established with well-replicated quantitative research. Here, we develop a continuous lichen conservation index representing epiphytic macrolichen species affinities for late successional forests in the Pacific Northwest, USA. This index classifies species based on expert field experience and is similar to the “coefficient of conservatism” that is widely used for evaluating vascular plant communities in the central and eastern USA. We then use a large forest survey dataset to test whether the community-level lichen conservation index is related to forest stand age. We find that the lichen conservation index has a positive, linear relationship with forest stand age. In contrast, lichen species richness has only a weak, unimodal relationship with forest stand age, and a binary indicator approach (where species are assigned as either old growth forest indicators or not) has a substantially weaker relationship with forest stand age than the continuous lichen conservation index. Our findings highlight that lichen communities can be useful indicators of late successional habitats of conservation concern, and that indicator systems based on expert experience can have strong biological relevance.

The importance of representative inventories for lichen conservation assessments: the case of Cladonia norvegica and C. parasitica

Conservation assessments of lichens have usually been based on scattered and methodologically diverse data. We illustrate the contribution of standardized inventories to conventional data sources by assessing the status of two conspicuous epixylic Cladonia species of conservation concern in Estonia. A time-limited inventory of all lichen species was carried out in 92 stands (2 ha each) in a balanced design of forests and clear-cuts. Cladonia parasitica (previously considered Regionally Extinct) was present in 13 stands with a total of 33 individual records, almost exclusively in dry boreal old-growth forests and clear-cuts. Thirty-six records of C. norvegica (previously six records) were made in 17 stands, most frequently in mature meso-eutrophic forests. On average, 1·5 hours of inventory were needed to discover C. parasitica in a stand, and 2 hours for C. norvegica. The scarcity of old records was probably due to the low local abundance of the species, their habitats being unpopular among lichenologists and expenditure of too short an inventory time in the field. Using habitat and frequency data, we estimate that the national population sizes of the species clearly exceed those set as IUCN criteria for species at risk. The key issue is the expected trend in substratum abundance, which suggests C. parasitica to be Near Threatened. We recommend stratified random sampling as an efficient method to collect quantitative information for lichen flora assessments.