We examined the influence of tree- and stand-level conditions on lichen diversity on 143 ash trees, varying in age from 11 to 140 y, in 5 deciduous stands in southern Sweden. The number of lichen species per tree varied from 2 to 30 and was primarily explained by tree trunk diameter and to a lesser extent by tree age, crown cover, lichen cover, and stand identity. The positive relationship between species richness and lichen cover seems compatible with a random placement of species and suggests that similar factors affect both lichen growth and establishment. Species richness did not increase on trees above 65 y of age, while species composition changed with tree age. Together with the positive linear effect of trunk diameter, these results suggest a slight overall positive effect of area, but that species richness over time depends more on species turnover. In addition, we examined if lichens occurring on trees of different ages differed in life history traits, e.g., spore size, thallus height, and pH preference. The results indicate that lichens that most frequently occurred on old trees had larger spores and thicker thalli than other species, suggesting that lichen species' response to tree age can be understood to some extent from their life history traits. However, in this respect lichen ecology is still in its infancy.

Nomenclature: Santesson et al., 2004.