Resampling epiphytic lichens in coniferous forests of the Southern Alps: Veteran trees promote compositional stability

In this study, by means of resampling epiphytic lichens in a timespan of fifteen years in forest stands of the Paneveggio-Pale di San Martino Natural Park (N Italy – Southern Alps), we aim at detecting changes in lichen assemblages by comparing temporal β-diversity patterns between tree individuals of different ages and considering the response pattern of thallus growth forms. Our results indicate that on veteran trees lichen composition seems to be more stable over time. This view is corroborated by lower values of temporal beta-diversity as compared to young trees which are more prone to changes of their lichen biota. In this perspective, dynamics of gains and losses, that translate into compositional changes over time, seem to be more rapid on young than on veteran trees. While the results on the overall dynamics of gains and losses in terms of taxonomic changes are still difficult to interpret, the frequency changes of different thallus growth forms are more explicit in the time frame of our study, indicating a decline in broad-lobed foliose and alectorioid lichens. Overall, our results further support the importance of retaining and increasing the occurrence of veteran trees for long term lichen conservation.