The epiphytic lichen biota of Caucasian virgin forests: a comparator for European conservation

The north-western Caucasus is exceptional in Europe because of its 1.3 million hectares of unmanaged 'virgin' forest. The Caucasus State Nature Reserve protects some 200,000 hectares, but contiguous areas are exposed to forest loss, fragmentation and degradation. Such an extensive region of virgin forest provides a unique opportunity to document diversity along key ecological gradients for an undisturbed system in Europe. Focusing on lichen epiphytes, we surveyed local diversity hot-spots along a 1200 m altitudinal gradient. Our main results are that: (a) species richness is enormously high in 1-hectare plots (between 233 and 358) representing a new baseline for Europe, (b) species composition differs substantially among plots with turnover increasing for difference in altitude. Cumulative species richness along the gradient was 597. More than a half of detected species had an affinity for, or were restricted to either the lower or the uppermost parts of the altitudinal gradient. However, this was related to differences in forest structure, rather than altitude per se. Species richness in plots increased significantly with the proportion of sparse/open forest. Length of an ecotone line, number of available tree and shrub species and number of dominant tree species also tend to increase species richness. These four variables had higher values at the lower and upper parts of the gradient, than at mid-altitudes, explaining a bimodal relationship of species richness with altitude. We conclude that loss of forest habitat at the lower and upper margins of the altitudinal gradient will cause the most significant decline in epiphytic lichen diversity.