Epiphytic lichens belong to the prominent indicator groups for changes in forest ecosystems. Owing to a finely balanced but disturbance-prone symbiontic relation between fungi and algae, lichens react quicker and more sensitive to changes in site conditions and their direct environment than higher plants, fungi and animals.
Forestry practices, a main factor for the decimation of lichen biota
A main factor for the decimation of lichen biota besides the air pollution during the last decades is modern forestry practices. The conversion of broadleaved and mixed forests to coniferous forest types, clear cuts, site amelioration due to fertilizing and compensation liming, the use of biocides and the consequent removal of all fallen and standing deadwood lead to a severe impact on lichen synusia on a long term. The intensive coverage of forest roads, skidding roads and tracks, the extensive draining of wet forest sites and peat bogs as well as frequent and intensive thinning practices changed the stand climate which is so important for many lichen species and lead to an enormous decline of lichens. Another reason for the decline of lichen species is currently shortened rotation periods or early harvesting of economically important tree species. Those trees are usually removed in establishment and removal cuts long before specialized lichen species are able to colonize potential deadwood candidate trees. The successional stage for typical lichen of old-growth forests cannot be established or is interrupted abruptly and therefore, many specialized species lose their habitat and go extinct.
Even a ecologically sustainable forest management is not able to ensure the diversity of lichen biota
A recent study in the National Park Bavarian Forest in Southern Germany suggests that old and near-natural forests have a significantly higher diversity of lichen compared to forests which experience a stronger influence of management. The sample areas in the managed forests contained 4 species on average whereas the samples in old forests exhibited 13 epiphytic species, a clearly lower diversity. An explanation for these findings may be that the old-growth phase of the managed forests is about 150 years shorter than in near-natural stands. The typical decaying phase of primary forests with a large proportion of deadwood and high biodiversity is completely lacking in those managed forests. As a conclusion might be said that even a multi-functional forest management is not able to ensure a sustained diversity of lichen biota. For the conservation of epiphytic lichens segregative as well as integrative measures will be necessary:
Protected areas for specialists with rare habitats (segregation)
- Evenly distributed and cross-linked strictly protected nature reserves on a large scale in all forest associations
- New National Parks centered in the realm of natural beech forests as future habitats and as indispensible gene reservoir for relict species of primary forests.
Conservation standards in managed forests for habitat management for generalists (integration)
- Creation of diverse forest structures with a high proportion of broadleved species
- Minimal impact forestry with a reduced impact on changes of the meso-climate through selection cutting and other single-tree or small-group methods
- Increasing the amount of large diameter deadwood
- Permanent preservation of evenly distributed habitat trees and old tree groups
- Strict protection of old trees
- Maintenance of traditional silvicultural methods and other special sites
- Reduced reforestation of clear-cuts
- No large-scale fertilizing
by Johannes Bradtka