Long-term implications of sowing legume-rich mixtures for plant diversity of Mediterranean wood pastures

摘要

Wood pastures grazed extensively are acknowledged as high biodiverse agroecosystems. The economic sustainability of these so-called high nature value farms has been questioned because of the low quality and productivity of their pastures. Farmers frequently improve the productivity of native pastures by sowing legume-rich mixtures. However, the consequences of this practice for the local biodiversity are still unknown. The study aimed to assess the long-term implications of sowing legume-rich mixtures on the plant diversity of Mediterranean wood pastures. We sampled plant species composition, both beneath and outside trees, in seven farms that included a chronosequence of legume-rich pastures, sown in different years (from 2002 to 2015), and an unsown plot. Plants were sampled during two years, 2016 and 2017, a typical and a very dry year, respectively. Results revealed that legume abundance significantly increased after showing, but it faded with time. Similarly, the richness of legume species also showed a transient increase. Overall plant richness at plot scale (a-diversity) did not show any effect. At a larger scale, gamma-diversity was dominated by beta-diversity, the only biodiversity component slightly affected by sowing in the long-term. Species composition significantly differed between habitats, beneath and outside the tree canopy, and among plots of different ages, despite being sown species common in old plots. Communities growing beneath tree canopies showed fewer differences between years or among plots of different ages than growing outside, suggesting a buffering effect of trees. We conclude that sowing legume-rich mixtures on native pastures of Iberian dehesas can be a cost-efficient way of meeting farmers' needs from a respectful biodiversity point of view.