RESUMEN
1.: One approach to biodiversity conservation is to set aside small woodland key habitats (WKHs) in intensively managed landscapes. The aim is to support species, such as epiphytes, which often depend on old trees and are negatively affected by intensive forestry. However, it is not known whether the number of host trees within these areas can sustain species in the long term. 2.: We studied metapopulation dynamics and assessed the future persistence of epiphytes assuming host tree numbers similar to those observed in large north European WKHs. The study species were seven cyanolichens confined to Populus tremula in the boreal study area. Colonizations and extinctions were recorded in 2008 on trees that had been surveyed 13 years earlier. We applied generalized (non)linear models to test the importance of environmental conditions, facilitation and spatial connectivity on the metapopulation dynamics. We also simulated the effects of tree numbers and tree fall rates on future species persistence. 3.: Metapopulation dynamics were explained by tree quality, size or tree fall. In one species, colonizations increased with increasing connectivity, and in a second species it increased if other lichens sharing the photobiont with the focal species were present, suggesting facilitation. Both stochastic extinctions from standing trees and deterministic extinctions caused by tree fall should be accounted for in projecting epiphyte metapopulation dynamics. 4.: One to three infrequent, sexually dispersed study species face a significant extinction risk within 50 years, especially in areas with low tree numbers. 5.: Synthesis and applications. During the coming decades, infrequent, sexually dispersed, epiphytic lichens are likely to be lost from small woodland habitat set asides in intensively managed landscapes. Local extinction will be a consequence of low colonization rates and tree fall. Low colonization rates can be prevented by retaining large trees on which lichen species colonization rates are the highest and by assuring a high density of occupied trees. The negative effect of tree fall should be compensated for by assuring continuous availability of old trees. This can be achieved by decreasing the populations of large browsers, or by retaining trees with high conservation value during management operations.
RESUMEN
Here, cyanobiont selectivity of epiphytic lichen species was examined in an old growth forest area in Finland. Samples of the eight lichen species were collected from the same aspen (Populus tremula) and adjacent aspens in the same stand. The cyanobionts of these samples were compared with free and symbiotic Nostoc obtained from other habitats and geographic regions. Our results, based on the phylogenetic analysis of a partial small subunit of the ribosomal DNA (16S rDNA) and the rbcLX gene complex did not show any correlation with the geographic origin of the samples at any spatial scale. Instead, there was a correlation between the cyanobionts and the alleged taxonomy of their mycobionts. The results indicate that the lichen species examined are highly selective towards their cyanobiont partners. Only Lobaria pulmonaria proved to be more flexible, being able to associate with a wide range of Nostoc. A same Nostoc strain was found to form associations with taxonomically unrelated lichens indicating that the cyanobiont-mycobiont associations as a whole were not highly specific in the examined species.
