Ecología de laderas restauradas de la minería de carbón a cielo abiertointeracciones ecohidrológicas

Résumé

Coal mining restoration is a complex activity. The construction of these new environments includes the natural processes framed within ecological succession. Ecohydrological processes are key for the functioning of these new ecosystems. The key factors of the ecohydrological dynamics in rilled restored slopes, characterized by "arrested succession" are well known. However, there is a scarcity of studies on slopes under sheet flow processes where ecological succession could have a greater potential to achieve revegetation. The main objective of this PhD thesis was to study the interaction between vegetation and overland flow and its relationships with ecological succession patterns, focusing on the effects of overland flow routing along the slope on these interrelationships. The main hypothesis is that the interaction between overland flow and vegetation is a key phenomenon that directs the spatial structure and the functioning of these systems, and in particular, that overland flow is a driving force for ecological succession (agradation). In a first study at the regional scale, strong interactions between overland flow and vegetation in non-rilled restored slopes were described, identifying "ecohydrological units" that are characterized by a specific floristic composition and hydrological behaviour. Rilling processes were identified as degradation processes in which the control of hydrology is directed by abiotic elements of the ecosystem. Moreover, we identified that the strength of ecohydrological interactions is lower in vegetated slopes, due to the absence of overland flow processes. Afterwards, an experiment was carried out in three restored slopes subjected to different volumes of overland flow routing along the slope caused by differences in up-slope structures. These slopes span a gradient of overland flow from discontinuous rilling to mild sheet flow. In this context, the influence of vegetation on the spatial heterogeneity of hydrological processes was analyzed, identifying runoff sinks and sources. Additionally, we investigated the influence of overland flow routing along the slope on hydrological heterogeneity, concluding that overland flow controls "hydrological diversity": as the overland flow volume increases, hydrological diversity decreases, developing opposite hydrological behaviours (extreme sources and sinks). We also explored the effect of the spatial distribution of soil moisture -conditioned by ecohydrological units- on vegetation composition, structure and dynamics, together with the limiting factors for vegetation colonization, related to the overland flow volume routing along the slope. The functional relationships between runoff sources and sinks were analyzed, considering the ecological effects of runoff exclusion along an overland flow gradient at the slope scale. In summary, we proved that the TTRP (Trigger Transfer Reserve Pulse) framework -which explains ecohydrological interactions in semiarid environments-, can be used in these restored environments. This conceptual framework has never been applied in restored environments, where it can have practical implications for the development of appropriate restoration strategies. The results obtained in this PhD thesis highlight that when overland flow volumes are reached, vegetation patches are highly dependent on overland flow and the control of water resources is abiotic. However, under low overland flow volumes routing along the slopes, water control is biotic, and a shrub species appears (Genista scorpius) which is able to modify runoff redistribution patterns and whose biotic interactions (facilitation) can direct the system towards a vegetated slope. In conclusion, overland flow volume influences the control of water resources, hence, it directs successional processes in these restored slopes. The identification of overland flow as a driving force in these restored environments calls for its incorporation in restoration projects. As a result, the concept of "runoff expert management" emerges, which should be delved into and applied to mining restoration projects in order to achieve a correct evolution of these restored environments.