Some factors affecting successional change on uranium mine wastes: Insights for ecological restoration

Question: Are growth form and dispersal-mode replacement during vegetation succession in semi-arid Mediterranean conditions affected by the starting quality of the substrate and by site aspect? Location: Central-western Spain. Methods: We monitored successions on three waste materials left after uranium mining: unbroken waste, broken waste and wastes amended with a sandy material (Arkoses); both north and south aspects were also studied on each substrate. Results: The substrate starting quality had the greatest influence on spontaneous succession, separating the poorer quality substrates (broken and unbroken wastes) from the better ones (Arkoses) and two reference communities (Topsoil and Dehesa). The importance of aspect was confirmed then within each substrate type. Most species with a short life span (mostly annuals and a few biennials), together with some woody species on Arkoses, showed no response to age (years following the deposition of new soil). Others short-lived species declined over time on the poorer wastes but not on the better Arkoses. There was a tendency for life form replacement (from thero-phytes to hemicryptophytes) during succession only on the poorer-quality substrates. No dispersal-mode replacement sequence was found. Conclusion: Improving the abiotic conditions of the substrate had a great effect on vegetation succession, but this effect was modified by aspect. Aspect took longer to induce differences in floristic composition on the poorer substrates, where succession was slower. Some trends in species responses to successional change were found by considering species traits, particularly life-form.