In restoration, emphasis is given first to build soil organic matter, nutrients and vegetation cover to accelerate natural recovery process. Tree plantations can be used as a tool for mine spoil restoration as they have ability to restore soil fertility and ameliorate microclimatic conditions.
Strip-mining can cause soil compaction, changes in soil texture, loss of soil structure and reduced water infiltration.
Sparse vegetation growth on abandoned mine soils also results from low organic matter.
Plantations can play a critical role in restoring productivity, ecosystem stability and biological diversity to degraded areas. Relative to unplanted sites, plantations have a marked catalytic effect on native forest development (succession) on severely degraded sites.
Trees can potentially improve soils through numerous processes, including maintenance or increase of soil organic matter, biological nitrogen fixation, uptake of nutrients from below the reach of roots of understory herbaceous vegetation, increase water infiltration and storage, reduce loss of nutrients by erosions and leaching, improve soil physical properties, . . . and improve soil biological activity. Given time, new self-sustaining top-soils are created by trees.
Numerous studies have demonstrated that land rehabilitation benefits from plantations because it allows to jump-start succession. The catalytic effects of plantations are due to changes in understory microclimatic conditions (increased soil moisture, reduced temperature, etc.), increased vegetational-structured complexity, and development of litter and humus layers that occur during the early years of plantation growth. The development of a plantation canopy can alter the understory microclimate and the soil physical and chemical environment to facilitate recruitment, survival and growth of native forest species. Otherwise, native species would only very slowly, if ever, regenerate on degraded sites. Thus plantations may act as “foster ecosystems’, accelerating development of genetic and biochemical diversity on degraded sites.
Plantations have an important role in protecting the soil surface from erosion and allowing the accumulation of fine particles. They can reverse degradation process by stabilizing soils through development of extensive root systems. Once they are established, plants increase soil organic matter, lower soil bulk density, moderate soil pH and bring mineral nutrients to the surface and accumulate them in available form. Their root systems allow them to act as scavengers of nutrients not readily available. The plants accumulate these nutrients and re-deposit them on the soil surface in organic matter, from which nutrients are much more readily available microbial breakdown.
Most importantly, some species can fix and accumulate nitrogen rapidly in sufficient quantities to provide a nitrogen capital, where none previously existed, more than adequate for normal ecosystem functioning. Once the soil characteristics have been restored, it is not difficult to restore a full suit of plant species to form the required vegetation. According to Faulconer et al, other advantages are that establishment of desirable tree species capable of maintaining the site will slow or prohibit invasion of less desirable weed species, will provide economic returns in the long term, will aid in developing wildlife habitat and will promote hydrologic balance in the watershed.
Reclamation is the process by which derelict or highly degraded lands are returned to productivity, and by which some measure of biotic function and productivity is restored. Long-term mine spoil reclamation requires the establishment of stable nutrient cycles from plant growth and microbial processes. However, the reclamation process often becomes arrested because of severe limitations in the site or the biota.
Ecological restoration concentrates on processes such as persistence of species through natural recruitment and survival, functioning food webs, system-wide nutrient conservation via relationships among plants, animals and the detrivore community.
The process of natural succession on surface-mined soils is slow due to the removal of topsoil, resulting in elimination of soil seed bank and root stocks and due to soil profile disturbances. As many as 50 or 100 years can elapse before a satisfactory vegetation cover develops on mine waste. Redevelopment of advanced communities may take a millennium or more.
An important goal of ecological rehabilitation is to accelerate natural successional processes so as to increase biological productivity, reduce rates of soil erosion, increase soil fertility and increase biotic control over biogeochemical fluxes within the recovering ecosystems. Analysis of different natural successions on natural and artificial substrates suggests that one of the important factors limiting the rate of development is the process of immigration of taxa. There are genuine difficulties in appropriate species reaching a particular site. Artificial re-vegetation is often used to facilitate the generally slow natural rehabilitation process.