Substrate-specialist plants for restoring vegetation in post-mining gypsum substrates

Abstract

Restoration in degraded gypsum areas is challenging due to physical-chemical soil characteristics that limit plant development. Facilitation mediated by the stress-adapted gypsophytes may be a key process in restoration because it potentially favors the establishment of lower stress-adapted species underneath, promoting plant succession. This study aimed to assess the suitability of the gypsophyte Gypsophila struthium Loefl. for restoring vegetation in gypsum mines, focusing on its role as a pioneer species that may act as an ecosystem engineer and hence as a nurse plant. We conducted a vegetation survey in a gypsum mine in NE Spain, in plots where the original topsoil was reinserted in different years after the mineral extraction to study plant community succession and reorganization through time. Complementary, we set a sowing and planting experiment in a gypsum spoil dump to assess how G. struthium may positively affect soil and micro-environmental conditions and, consequently, may act as a nurse species facilitating plant establishment and development. To test the nurse role of G. struthium, we sowed seeds and planted seedlings of Helianthemum squamatum (L.) Pers. and Stipa lagascae Roem. & Schultz under the canopy of adult individuals of G. struthium, and in the bare soil. We found that G. struthium appeared as a pioneer shrub in the restored gypsum mine and accumulated plant diversity in the local vicinity in mature plant communities. This shrub had a positive effect on seed germination and seedling growth of the test species in the experiment and improved soil and micro-environmental conditions under its canopy. Therefore, we recommend two non-exclusive actions to enhance restoration in post-mining gypsum substrates: (1) to promote the establishment of the pioneer plant G. struthium by improving the physical-chemical and biological soil properties through the re-insertion of the original topsoil that contains propagules of the former community; (2) to apply active restoration actions, using G. struthium as a nurse plant through sowing seeds or planting seedlings of other species of interest under its canopy.