Influencia de factores abióticos en la revegetación temprana tras hidrosiembra de estériles de carbón - influence of abiotic factors in early revegetation after hydroseeding of coal mines

Resumen

Open cast mining generates large environmental impacts where there are statutory or planning requirements to ensure restoration. In such damaged systems the aim of the ecological restoration should be to develop a long-term self-sustaining ecosystem, which resembles the natural ecosystems that were present before the mining operations took place. Nevertheless, the effective restoration of mines is a complex process, hampered mainly by the complete removal of vegetation and soil disturbance. As the restoration is implemented, there is an excellent opportunity to study the successional dynamics of vegetation development and its constraints in these newly-created ecosystems. This thesis analyzed the vegetation succession processes after the restoration of open cast coal mines located in the Palencia province (Spain). The study was performed at two scales: short term (1-6 years after restoration) and medium term (1-40 years after restoration or abandonment), with the aim of providing recommendations for the effective restoration of these areas. In short term the aim was mainly to analyze the success of the restoration and the factors influencing the vegetation establishment, while the medium-term aim was to describe the species turnover and the potential successional constraints. In short term, hydroseeded species were successful in slopes revegetation, mainly during the first two years. Native species, forced to colonize from the surroundings by the absence of a seed bank in the soil, increased in number and cover with age. Stochastic factors (climate and colonization) or abiotic (topography) played an important role in the composition and abundance of both native and hydroseeded species. In contrast, soil factors did not control species composition during succession, but some of them changed during the successional process (increase of organic matter, sand content), thus creating better conditions for subsequent native species establishment and development. The species composition and vegetation structure (richness, diversity and cover) was converging with the reference community in the six years after restoration. The medium-term plant succession was conditioned by the restoration method used; whether topsoil was added or not. In non-topsoiled mines, substrate-based constraints arrested succession leading to the formation of a community characterized by early-successional species. In contrast, top-soiled mines showed the classical pattern of species turnover, with annual and perennial species richness peaks and an increasing complexity in vegetation structure during succession. From environmental and soil variables only age since restoration and pH conditioned the succession, although it moved in the desired direction approaching the composition of native vegetation, developing a native shrub community in 15 years and a young forest in 30 years.