Soil and vegetation development during early succession on restored coal wastes: a six-year permanent plot study

Aims Little is known about how soil parameters change during early stages of revegetation dynamics on newly-restored coal mines, particularly in a Mediterranean climate. Our aim was to explore the short-term interactions of changes in soil physico-chemical properties and vegetation succession (composition and structure) in these newly-forming ecosystems, and discuss potential functional relationships. Methods Between 2004 and 2009, we monitored soil and vegetation changes in nine permanent plots (20 m2 each one) at a restored open-pit coal mine annually; these plots were set up in a structured way to account for site aspect (north, south and flat). We used linear mixed models and multivariate analysis to derive patterns of soil parameters changes through time and to relate soil variables with vegetation structure or floristic compositional changes. Results Soil variables showed a general trend over time of increasing soil organic matter, total carbon and nitrogen, sand content and exchangeable calcium, but a reduction in soil pH, clay and lime contents, whereas electrical conductivity, P, Mg2+ and K+ showed no change through time. More importantly, these changes in soil properties were independent of aspect, whereas vegetation functional/structural changes were related to the accumulation of organic matter and sand content, and pH reduction. Surprisingly, floristic compositional changes had little relationship with soil factors. Conclusions The results indicate that age since restoration was the main driving agent, at least in the short-term, of soil and vegetation compositional changes during ecosystem development through the restoration of a coal mine, whereas vegetation functional/structural changes are involved in the mechanism that induce some soil changes, favouring the increase of plant community complexity in such mined areas. Finally, these results suggest that if soil-forming material is sufficiently good for vegetation development, floristic compositional differences are mainly driven by a combination of abiotic and stochastic factors in the short-term.