Detection probability and abundance estimation of epiphytic lichens based on height-limited surveys

Questions What are the detection probabilities of epiphytic crustose lichens on oak (Quercus robur) when only the lowest 2 m of the trunk are surveyed? How does the abundance of lichen species change with height above the ground, and is the change related to tree age? How well can total abundance (0-6 m) be predicted based on data from the lowest 2 m? Which tree characteristics explain the vertical distribution of the study species? Location Southeast Sweden. Methods The occurrence and abundance of eight crustose lichen species were recorded on 35 oaks, 0-6 m from the ground. Results The detection probability was high (> 96%) for seven out of the eight species. The abundance of six species declined significantly with increasing height. For five species, > 69% of the total abundance (0-6 m) was recorded on the lowest 2 m. The proportion of the total abundance present above 2 m increased significantly with age for three species. Models predicting total abundance based on data from the lowest 2 m and diameter explained > 80% of the deviance for all except one species. The vertical distribution of the study species was explained by bark fissure depth, area and cover of macrolichens. Conclusions For crustose lichens associated with old oaks, surveying only the lowest 2 m of the trunk yields reliable occurrence data and fairly good estimates of total abundance. However, before interpreting data from the lowest 2 m, knowledge of species vertical distribution, and how the distribution changes with tree age is essential.