Influence of substrate age and quality on species diversity of lichens and bryophytes on stumps

Stumps from the last felling constitute a large proportion of dead wood in young managed forests. Yet, the knowledge of the diversity of stump-inhabiting organisms is poor. We studied the importance of substrate age and quality to lichen and bryophyte diversity on the cut surface of stumps in south-central Sweden. In total, we found 53 lichens and 35 bryophytes on 449 Norway spruce stumps in a forest stand chronosequence of four age classes: 4–5, 8–9, 12–13 and 16–18 years old stands. The influence of substrate age and substrate quality on species diversity differed between lichens and bryophytes. Lichen species richness was higher for age classes 2–4 compared to age class 1, whereas bryophyte richness was higher in age classes 3–4 than in 1. Further, lichen richness increased with increasing stump height and the presence of surface structural components (chairs and levels), which together with decay also influenced lichen species composition. Conversely, increasing stump height and the presence of levels decreased bryophyte richness, which in turn increased with increasing decay, surface area and number of surrounding trees and shrubs. Only decay explained differences in bryophyte species composition. Stumps in this region seem more important to overall lichen diversity, because there were on average more lichen species per stump and we only found common bryophytes but several uncommon lichens. The different responses of lichens and bryophytes to age and substrate variables indicates, however, the importance of including several organism groups in species diversity studies of dead wood.