Opportunistic vegetation in quarry soil restoration from semiarid South East Spain: Pines and spontaneous species

The objective of our study was to undestand the effect of two organic amendments on three planted autochthonous species in two substrates mulched with pine chips 6 years after starting an experimental restoration in a quarry for cement production in semiarid SE Spain. But because this kind of mulch contained pine cones and pine seedlings appeared after the first year of the restoration, new objectives were added to the initial one: to check if organic amendments influenced pine growth among planted vegetation and if there were competition between planted and non-planted species. Essential soil parameters, plant cover and diversity and pine growth were measured and statistically processed with correlation analyses, ANOVA and detrended correspondence analysis. Six years after restoration, organic amendments contributed significantly to explain the differences on the tested variables. The combined effects of the two substrates and the two organic amendments effectively enhanced soil properties recovery, but they also facilitated the establishment and entry of new species in addition to planted vegetation, driving a differential plant development. Planted vegetation cover and total plant cover from amended plots were double that of control plots. The number of pines, as well as their coverage, depended on the interaction between amendment type and substrate. Organic amendments favoured opportunistic species which, despite competing with those planted, helped to control soil erosion and enhanced pedogenesis. Pine chips used as mulch and derived pine seedlings, despite not entering the experimental design, might have some potential in the restoration of these particular degraded semiarid environments.