North-facing roadside slopes: Anthropogenic climate microrefugia for orchids

Facing global climate change is a great challenge for organisms. Numerous species respond to a changing climate by shifting their geographical ranges, adapting to the local climate or finding microrefugia to persist under unfavorable macroclimatic conditions. Orchids are frequently found in roadside verges, and it was demonstrated that roadsides could serve as refugia for them in a changing landscape. We investigated whether roadside slopes, facing different compass directions could serve as microrefugia for orchids, using our database spanning across 18 European countries. Our results showed that the probability of orchid occurrence in north-facing roadside slopes are greater than on south-facing slopes. Further, we found a significant difference in the probability of orchid occurrence in different exposures under unfavorable macroclimatic conditions. In south-facing slopes, the probability of orchid occurrence decreased with increasing annual mean temperature and increasing precipitation seasonality. This suggests that harsh microclimatic environments intensify the negative effects of the macroclimate in south-facing slopes. Moreover, roadside slopes with cooler microclimatic conditions might facilitate the persistence of orchids under a warming and increasingly stochastic climate.