Epiphytic mosses and lichens are very sensitive to air pollution. Their gradual disappearance from large cities and from the vicinity of industrialized complexes is due, mostly, to phytotoxicants. A simple method to map the long-range effect of air pollution on corticolous epiphytes is described. An I.A.P. or "index of atmospheric pollution" based on the number of species present, their coverage and frequency, and their specific tolerance to pollutants can be expressed quantitatively.

Although specialist pollination systems are often thought to be the outcome of selection, wide evidence exists for generalization within plant-pollinator interactions. We studied the pollination system and reproductive success of Calluna vulgaris (L.) Hull over 3 years in an Upper Ardennes site in Belgium. A wide variety of insect visitors was recorded including Hymenoptera, Diptera, and Lepidoptera. Relative abundance of families and species of visitors varied markedly among years except for bees. Bumblebees and honeybees were the most efficient pollinators at the study site. Syrphid flies, mainly large ones, acted as important co-pollinators because of their high relative frequency. Calluna pollen was also dispersed by wind, and insect-exclusion experiments demonstrated that wind pollination contributed to reproductive success. Following open pollination, fruit set was high, ranging from 82.0 to 97.2% and independent of sampling location. Mean seed number per fruit was less than maximum potential seed number and varied strongly among sampling locations. We discuss this pollination system (generalist insect and wind) in terms of the ecological and geographical success of the species.Key words: Calluna vulgaris, pollinator visitation, insects, wind pollination, reproductive success.

SUMMARYGenetic diversity, population genetic structure and gene flow in Calluna vulgaris (L.) Hull were assessed by means of seven allozyme loci scored in 18 populations from the South-Western area of the species' range. Genetic diversity was lower (H.^ = 0-20) than reported for long-lived widespread species but was characterized by a high number of alleles per locus (5'60at the species level) of which more than 70'-\) were rare. More than 95 "r, of genetic variation vi'as found at the intrapopulation level (G^T -0'047). High levels of past gene flow-were inferred, based on the allozyme data (A'^ = 5-2 from G^T, A''^, = 10-2 from the 'private allele' method). Calluna vulgaris exhibited several geographic patterns of genetic variation. Both cluster analysis, constructed with various genetic distances and principal components analysis showed that Spanish and Pyrenean populations were clearly different from those collected in the Massif Central and Belgium. Also, a trend for decreasing genetic diversity towards Northern populations was detected. These patterns might be related to the post-glacial history' of Calluna. In addition, it is shown that isolation by distance has played a role in the geographic shaping of genetic \'ariation in this species.

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