Development of technical possibilities to restore the ecosystems of quarry heaps

The increased global demand for energy has led to the opening of large mining areas worldwide. The largest commercially exploited oil shale deposit in the world (total amount of resources 7x10⁹ tons) is located in North-East Estonia. Mining is essential to provide the resources for industries but can result in a destruction of pre-mining and post-mining ecosystem. Restoring ecosystems is one of the most important aspects of contemporary environmental conservation. Naturally, vegetation and soil develop slowly in quarry areas, and so far, quarry reclamation has been in use. One of the primary challenges encountered in the reclamation of mined areas is the low water retention of the soil, known as hydrophobicity, which hinders the establishment of vegetation and soil development. The aim of current work is to find out the suitable technique and technology for the crust material to cover the planting surface that retains moisture and nutrients, which can be used in plant cultivation and ecosystem restoration when covering quarry areas. The goal is to promote plant growth and thus accelerate forest ecosystem establishment. Four test areas were selected: a technically reclaimed oil shale quarry, an unrecultivated sand quarry, a reclaimed gravel quarry, and an unrecultivated gravel quarry.The tree species used were pine (Picea abies), spruce (Pinus sylvestris), and hybrid aspen (Populus tremula × Populus tremuloides Michx). Planting density was calculated according to the recommendations of the Estonian State Forest Management Centre. In each quarry, 100 pines, 100 spruces, and 100 hybrid aspens were planted. The experimental design included a control variant, biochar, sheep wool pellets, sheep wool discs (that are used as mulching material), and two types of biodegradable mulch film, in two replications. The trees were planted in May 2023, and the monitoring of their survival is still ongoing. However, based on the preliminary results, it can be stated that biochar, sheep wool discs, and various biodegradable mulch films had a positive impact on the survival of forest trees. This research is supported by the Circular Economy program of the Environmental Investment Centre through a project with the number RE.4.09.22-0034 and by developmental project of Estonian University of Life Sciences “Valorization of sheep wool for agricultural utilization”.