Non-native tree plantations are weak substitutes for near-natural forests regarding plant diversity and ecological value

While near-natural forest stands are dramatically diminishing, monoculture tree plantations are rapidly spreading globally, including the eastern part of Central Europe. Tree plantations are regarded as simplified and species-poor ecosystems, but their functional and phylogenetic diversity and ecological value are still mostly unknown. In the present study, we investigated near-natural poplar forests and the three most common tree plantation types (native deciduous Populus alba, non-native evergreen Pinus nigra, and non-native deciduous Robinia pseudoacacia plantations) in the Kiskuns ' ag Sand Ridge, central Hungary. Our aim was to find out how different the species composition of the studied habitats is, how taxonomic, functional, and phylogenetic di-versity vary among the four habitat types (i.e., near-natural forests and three types of plantations), and what the ecological value of the studied habitats is. We found that the four habitat types had significantly different species compositions. Although each habitat contained some diagnostic species, near-natural forests had the highest number of diagnostic species. While many of the diagnostic species of near-natural forests were native shrubs, tree plantations had many weeds and non-native herbs as diagnostic species. Near-natural forests had the highest per plot richness of native species and the lowest richness of non-natives. Shannon diversity, functional diversity and phylogenetic diversity were higher in the near-natural forests and two types of plantations (Populus and Pinus) compared to Robinia plantations. Based on naturalness indicator values, near-natural forests were the least degraded and Robinia plantations were the most degraded. Near-natural forests contained the most species of high conservation importance. Overall, near-natural forests proved to be much more valuable from an ecological and conservation perspective than any of the studied plantations; conservation and restoration programs should therefore focus on this type of habitat. Among the plantations, Populus alba plantations are the best substitute option in most respects, although they harbored a relatively high number of non-native species. We suggest that the native Populus alba should be preferred to non-native tree species when plantations are established. In addition, decreasing the extent of Pinus and Robinia plantations is essential on the long run if we aim to maintain the ecological integrity of the region.

Automated summary

This study investigated the differences in species composition and ecological value between natural poplar forests and three common types of tree plantations in central Hungary. The results showed that natural poplar forests had the highest species richness and diversity and the highest ecological and conservation value compared to the plantations. The study suggests that conservation and restoration efforts should prioritize the protection of natural poplar forests.