BryoMicroClim: Collecting bryophyte-relevant microclimate data to assess the gap between macro- and microclimate

Significant mismatches between macro- and microclimates challenge our ability to accurately estimate the climatic conditions experienced by organisms and thus to predict responses to climate change. This study aims to evaluate the relationship between macro- and microclimate for small-scale plants such as bryophytes, which are highly dependent on local environmental conditions.

To achieve this, we established a Europe-wide collaborative network of bryologists (the BryoMicroClim project), to measure the microclimate experienced by a bryophyte species. The moss Hedwigia striata, evaluated as near-threatened in Europe (Hodgetts et al., 2019), was selected as the target species. This species grows mainly in forests or rocky areas. We selected 15 sampling sites across Europe, spanning a wide range of climate conditions (Portugal, Spain, France, Belgium, Wales, Scotland, and Sweden). In each site, mostly continuous forested areas, we measured air temperature and humidity using three dataloggers (Envloggers, Environmental loggers) installed near H. striata populations. In the Iberian Peninsula, we also installed other dataloggers (BtMs, Bryolichen Temperature Moisture), specifically designed to measure ambient temperature, humidity, and water content of nonvascular cryptogams.

We used the slope and equilibrium approach (Grill et al., 2022) to infer if the microclimate temperature and relative humidity variability (as measured by the in-situ dataloggers) is buffered or amplified in relation to the macroclimate variability (from ERA5-Land and ERA5 data). We observed that microclimate temperatures were buffered or amplified depending on site conditions. As hypothesized, microclimate temperatures had a buffered variability in dense forest sites. Our results suggest that collecting bryophyte-relevant microclimate data at fine spatial resolutions and long time scales will be critical to better understand the potential vulnerability of bryophytes to climate change.