Ecological Restoration of Limestone Quarries: a Case Study

摘要

Quarrying activities have extremely strong environmental impact resulting in a loss of ecosystem functioning. Limestone extraction entails significant visual impacts and degradation problems as a result of soil depletion and deep alteration to the original topography. The common method of quarry exploitation in platforms increases drainage and the physical and chemical erosion of the substrate, hindering natural germination and establishment of young plants, and thus delaying recolonisation. In addition, high dust deposition due to quarrying activity can hinder the development of intact plant communities. Natural colonisation of abandoned limestone quarries is slow. The time scales involved in the creation of new communities are not considered acceptable for reclamation or restoration. A reclamation project was conducted in a limestone quarry of the Serra da Arrabida (South-west Portugal), a natural park with a dense evergreen sclerophyllous shrub community, one example of well-preserved Mediterranean vegetation in Europe. The successive revegetation of quarry terraces results in distinct plant communities of different age and cover. We compare the revegetation of 5 abandoned platforms sequentially revegetated over the last 22 years, at 3 year intervals, to evaluate the establishment and growth of introduced species as well as colonization and succession of natural vegetation. The successive revegetation of each platform resulted in distinct plant communities, differing in age and cover. The evolution of soil characteristics was also evaluated as well as the contribution of different species to soil formation on the platforms. To evaluate the impact of dust deposition due to mining activity, the vegetation structure of the oldest platform was compared to a revegetated site of similar age but heavily affected by dust deposition. The obtained results allowed us to recommend strategies and to establish criteria for evaluation of the success of the revegetation in these degraded areas. The main purpose of this work was to obtain biological and ecological information about mediterranean species able to colonise these degraded areas through the evaluation of plant cover and composition in revegetated quarries. To fulfil this objective we developed studies: (ⅰ) to compare the establishment of plants on different platforms with different age, (ⅱ) to evaluate the development of the soils, (ⅲ) to assess the importance of these plantings for migration and establishment of other indigenous species, and (ⅳ) to evaluate the effect of high dust deposition on the vegetation succession.