Changes in the distribution of bryophytes in a highly urbanised region in Western Europe (Flanders, Belgium), a species traits analysis.

Introduction
In densely populated, highly industrialised regions such as Flanders (northern Belgium), species are under significant environmental pressures arising from air pollution, land use changes, and climate change, which affect distribution patterns and species abundance.

Methods
We compared bryophyte distribution data for 1980–1999 and 2000–2019. Species traits data were analysed to detect general trends in changes in occupancy for different species of moss and liverwort.

Key results
Species occupancy increased for epiphytic species of both mosses and liverworts. Liverwort species growing on dead, decorticated wood declined, whereas the number of mosses growing on this substrate increased. Liverworts decreased in all terrestrial habitats except artificial stones and other rocky substrates. Occupancy increased for mosses growing on peat substrates and on hard natural rocks. Changes in occupancy among groups of taxa classified according to Ellenberg values showed that liverworts of wet or moist habitats declined compared with those of dry habitats. Liverworts of warmer regions increased; however, for those characteristic of cold climates, there was no significant change.

Conclusions
Improvements in air quality, particularly due to reduced SO2 and NOx emissions, has allowed epiphytic bryophyte species numbers to recover. Among terrestrial species, there has been a decline in the number of liverwort species especially, and particularly those adapted to wet, cold conditions. This is probably due to longer and more frequent drought periods during summer, coupled with rising ambient temperatures. Larger, more robust wetlands and forests could be created to mitigate against this decline, these habitats being very fragmented in Flanders.