Vegetation recovery of gypsum quarries: short-term sowing response to different soil treatments

Question: How does the sowing of native species under different soil treatments contribute to the recovery of gypsum habitats affected by quarrying in Mediterranean environments? Location: Mediterranean gypsum outcrops in Granada (SE Spain; 37 degrees 2' N, 3 degrees 45' W). Methods: We conducted an experimental sowing of native perennial species from gypsum habitats (both gypsophiles and gypsovags) considering two factors: bedding materials and surface treatments. For bedding material we used: gypsum spoil, topsoil addition on gypsum spoil, raw gypsum and topsoil removal. The surface treatments were: control, sowing, sowing plus organic matter and sowing plus an organic blanket. There were five replicates per combination treatment (80 plots in total, of 25 m (2) each). The sowing was performed in Nov 2009. All subplots were monitored to estimate density, richness, survival, growth of seedlings and herbaceous biomass, in two monitoring periods (Jul and Oct). Results: No gypsophiles or gypsovags were found in the control plots (no sowing or surface treatment), and therefore natural succession proved ineffective in the first year. In contrast, sowing was very satisfactory, especially on gypsum spoil, where mean density was of more than 15 individuals m(-2). This result is noteworthy as this material remains after the end of gypsum mining activity. Spreading topsoil over gypsum spoil proved to be no more positive, since it provided not only seeds of target species but also of competitor species. Also, with regard to herbaceous species, this treatment produced a highly significant increase of biomass. The organic blanket increased plant density, whereas the addition of organicmatter had significant positive effects on survival and growth of the seedlings. The global high survival rate is remarkable, especially for the gypsum spoil treatment. Conclusions: We highlight the importance of implementing recovery measures in gypsum habitats. An appropriate selection of seed mixture and density, as well as the use of gypsum spoil (the most favourable bedding material, according the results), is sufficient to ensure presence of the key species. Both technical solutions tested, organic blanket installation and organic matter addition, improved the results in terms of density, survival and growth of the seedlings.