Recent declines and range changes of orchids in Western Europe (France, Belgium and Luxembourg)

In recent decades, many studies have documented local declines of orchid species due to environmental changes. However, few data are available about the changes of orchid species' distributions at large spatial and temporal scales. We aimed to characterize the recent dynamics of orchid distributions in Western Europe, in regard to (i) climate and land-cover changes and (ii) species' ecology (i.e. bioclimatic preferences and light requirements). We based our analysis on surveys made by the French Orchid Society on 134 orchid taxa in France, Belgium and Luxembourg over 20 years (i.e. before 1985 until 2005). We designed null models to assess the nature and significance of recorded changes within each administrative unit and for each orchid taxa. We found sharp declines of most orchids in the Northern part of the study area (i.e. Northern France, Belgium and Luxembourg) and many new appearances in the Central and South Western part of the study area. Heliophilous (shade-intolerant) species declined more than sciaphilous (shade-requiring) species, possibly due to the loss of open habitats in the Northern highly urbanized regions. No significant differences in appearance or disappearance were detected between Mediterranean and Euro-Siberian species. Our results suggest that climate change is not a primary driver of distribution changes over the period considered, compared to land-cover changes. Further declines in the Northern part of the study area will exacerbate the already existing contrast in species richness and related conservation priorities between the North and South of the study area.