Native and alien poplar plantations are important habitats for terrestrial orchids.

Poplar monocultures are some of the most common short-rotation coppices. While they are most often considered of low environmental value, they have recently gained recognition for their multifaceted role in ecological engineering, such as carbon sinks, soil remediators or green energy producers. Nonetheless, the biodiversity of poplar plantations remains little known and largely overlooked. Here we conducted a systematic botanical survey of 232 poplar plantations within the Pannonian ecoregion (central Europe) in order to assess their plant diversity, with particular focus on terrestrial orchids. Our results highlight that almost 60% of poplar monocultures harbour terrestrial orchids, some with several thousand specimens. Overall, we documented the occurrence of 15 species of terrestrial orchids in the surveyed plantations, including taxa with limited distributions and a threatened conservation status. For instance, we report numerous new populations of Epipactis bugacenis and E. tallosii in poplar plantations, suggesting that the majority of these taxa occur in poplar monocultures within Hungary. We analysed and highlight soil chemistry and plantation characteristics that predict the occurrence and species richness of terrestrial orchids in poplar monocultures. The probability of orchids being present is highest in older and larger poplar plantations, characterized by high total organic matter content and high soil pH. We conclude that plantations of native and alien poplar harbour valuable plant communities, including terrestrial orchids and other vascular plants of significant conservation importance. Using the knowledge generated here, we recommend delaying or partial harvest of poplar plantations to increase their conservation potential.