Format: ORAL

Tim Claerhout1, 2, Michael Stech2, Paul J.A. Keler1, Laurens B. Sparrius3

1 Hortus botanicus - Universiteit Leiden, Leiden, the Netherlands 2 Naturalis Biodiversity Center, Leiden, the Netherlands 3 Dutch Bryological and Lichenological Society (BLWG), Utrecht, the Netherlands

With the increasing urbanization and likelihood of extremely hot summers due to climate change, there is a need for investigating the impacts of the urban environment on the species communities living therein. Two ubiquitous, but often overlooked species groups are lichens and bryophytes, which have a historic background as bio-indicators. Here, we explore for the first time whether the urban heat island influences the diversity and distribution of lichens and bryophytes living epiphytically on urban trees. Additionally, we investigate the possibility of using these two groups as bio-indicators for the urban heat island. Furthermore, we will investigate the patterns of temperature and humidity in different urban settings on a smaller scale using sensor data and link this with the prevalent lichen and bryophyte diversity. We conducted vegetation surveys on Tilia trees in three cities in the Netherlands (Amsterdam, Leiden and Rotterdam) and analysed species diversity and distribution patterns. Based on an indicator species analysis, we defined groups indicative for different levels of heat stress. For example, acrocarpous mosses are indicative for urban regions with much heat stress, whilst crustose lichens with photobionts belonging to the genus Trentepohlia Martius, 1817 are more indicative for the outer semi-rural regions. These results will be further analysed in relation to urban microclimate (temperature and humidity using sensor data) and are also being implemented in a citizen science project.