Opencast mine restoration in a Mediterranean semi-arid environment: Failure of some common practices

Abstract

Restoration works in opencast mining are mostly done with fast-growing herbaceous species to control the erosion of embankments during rainfall, especially immediately after their construction. Such species often exhibit a high demand for water and their survival is therefore associated to an adequate hydric supply. If this fails, these species can rapidly disappear when water is scarce. This paper shows the results of a restoration experiment where two stony mineral substrates were used in a quarry area (NE Spain). The experiment was carried out at lysimeter scale and the aim was to evaluate the short time vegetation response to common restoration practices in semiarid areas with two types of substrates and two types of irrigation practices. Lysimeter results were used to indirectly draw implications for the usual irrigation practices in the area.During periods of the first year after sowing, irrigated and non-irrigated lysimeters were monitored for substrate humidity, water leachates and plant development. The population cover of sown plants fluctuated according to the water availability in the substrate before drought. Density of total basal shoots decreased dramatically during the period of water stress, reaching negligible cover values on both types of substrates.Water content in the top substrate (0–20cm) was dramatically reduced in June, just after the maximum plant cover and water demand were reached (May).According with our results, it is not advisable to aim at a continuous and dense herbaceous cover composed of species that are not drought tolerant in restoration works, especially if embankments are constructed with spoil mine substrates. The restoration of opencast areas should include the use of water stress-resistant plants and careful irrigation plans.