Restoration of ecosystems on post-mining and post-industrial sites represents an important part of contemporary restoration ecology. Over the globe, about 1 % of land surface was directly influenced by mining activities (Walker 1999) and if we include various post-industrial sites, such as, for example, ash and other waste deposits, the figure may increase. Mining is known to have dramatic environmental impacts. Besides that it strongly degrades or destroys natural ecosystems, the impacts may be reflected to human health, e.g., through the contamination of water and air (Palmer et al. 2010). Restoration and reclamation of post-mining and post-industrial sites aim at mitigating the adverse impacts of mining on the environment and human health. Regeneration is, however, a long process, as affected ecosystems have lost their biodiversity and most of their ecosystem functions and services. Several approaches and measures are therefore used to bring back the lost ecosystems or to replace them by alternative ecosystems that withstand the degraded conditions (Bradshaw 2000).
Restoration of biodiversity and ecosystem services in post-mining and post-industrial sites has received wide attention among restoration scientists. The 9th European Conference on Ecological Restoration (SER 2014) held in Oulu, Finland, on August 2014, was not an exception. Almost 400 participants from 36 countries from science, EU policy, management, private companies, consultancy firms, and NGOs gathered together to discuss the integration of ecosystem service and land use questions to the context of ecological restoration. Many papers in this volume were presented in the conference session “Mineral extraction sites: restoring biodiversity and ecosystem services” where in a total of 12 oral presentations and five posters were shown. By collecting an edited selection of SER2014 conference presentations and other selected papers, this special issue provides an overview and appraisal on how the biodiversity and ecosystem services concepts have been incorporated into the restoration and reclamation of post-mining and post-industrial sites.
Biodiversity and ecosystem services
Ecological restoration aims at increasing the biodiversity and ecosystem functions or services (Whisenant 1999; Farber et al. 2006). Ecosystem services targeted initially in post-mining and post-industrial sites are related to soil physical characteristics, such as erosion control, water filtration, and the improvement of the micro- and mesoclimate, which are prerequisites for the establishment of permanent vegetation. Thereafter, the target services can be the re-establishment of productive sites, carbon sequestration, and the increase of the aesthetic value of the site or the landscape. Ecologists preferably emphasize the re-establishment or increase of biodiversity as a goal of restoration. Because biodiversity is seen to be associated with the increase in ecosystem functions or ecosystem services (Rey Benayas et al. 2008), it is commonly used as a core criterion or as a surrogate of ecosystem “health.” The term biodiversity can be understood as the diversity of species, functional groups, food webs, or genetic structure of populations (Gaston and Spicer 2004). Although species diversity is a useful and often easily measured criterion in restoration projects, it may be insufficient and even misleading in some cases. For example, high species diversity may indicate that there are both target species (SER 2004) and competitive generalists, sometimes alien species, at the restored site. The latter may signal an unwanted regeneration pathway (Kopeć et al. 2015). Selecting biodiversity indicators in mining and restoration projects implies making choices based upon values and focusing on some aspects that can be managed (Pitz et al. 2015).
Ecological restoration and reclamation
Passive restoration (Holl and Aide 2011), also known as spontaneous succession (Prach and Pyšek 2001), forms one end of a continuum of ecological restoration intervention levels (Prach and Hobbs 2008; Holl and Aide 2011; Walker et al. 2014). Passive restoration involves no or few active restoration measures, and the ecosystem is expected to recover principally through natural succession. The other end of the continuum is technical reclamation which is often applied to heavily disturbed sites such as mining and other industrial sites. Technical reclamation involves heavy interventions such as the restructuring of landforms, importing soil, and planting or sowing of plants. The target ecosystem may not always be the originalecosystem lost by mining or industrial activities, but a system that is considered useful for some purpose (SER 2004), for example forest management (Metslaid et al. 2015). Intermediate interventions are called assisted restoration and may include an ecologically justified enhancement of abiotic site conditions, the suppression of undesirable species, planting or sowing target species, and creating microsite heterogeneity. At mining and industrial sites, assisted restoration aims at speeding up the natural regeneration of the ecosystem, which might otherwise be very slow, for example, due to adverse (cold, dry, wet, nutrient poor, polluted) conditions.
In the papers of this issue, attention is given to passive restoration and the factors influencing spontaneous succession (e.g., Nikolic et al. 2015; Tropek et al. 2015; Horáčková et al. 2015; Alday et al. 2015), to field experiments comparing ecological restoration measures (Tarvainen and Tolvanen 2015; Karofeld et al. 2015), to the comparison between reclamation and passive restoration (Řehounková et al. 2016; Šebelíková et al. 2015), and to the reclamation by afforestation (Metslaid et al. 2015). Based on the results, passive restoration seems to be an effective approach at many post-mining and post-industrial sites (but see Kopeć et al. 2015), whereas technical reclamation may have negative effects on the biodiversity, since it decreases the amount of habitats for specialized threatened species (Tropek et al. 2015; Řehounková et al. 2016) or maintains the pool of seeded alien species that may spread to the surrounding environment (Rydgren et al. 2015). On the other hand, technical reclamation can be justified through the economic profit as in the case of timber production of afforested sites (Metslaid et al. 2015). Experimentally tested ecological restoration measures (Tarvainen and Tolvanen 2015; Karofeld et al. 2015) and analyses of environmental and plant characteristics influencing the regeneration and succession (Boisson et al. 2015; Alday et al. 2015; Nikolic et al. 2015) provide scientific information that can be used in developing effective ecological restoration under adverse conditions. A special and, in some cases, the only possible restoration measure is the ex situ conservation of endangered species which can be later used in ecological restoration projects (Le Stradic et al. 2015).
What is the restoration target?
Undisturbed neighboring ecosystems such as forests (Alday et al. 2015; Tarvainen and Tolvanen 2015), peatlands (Karofeld et al. 2015), and the tundra (Rydgren et al. 2015) may be used as a reference for ecological restoration, but they may not always be a valid reference for large-scale mining or industrial sites. An alternative stable state should also be considered (Alday and Marrs 2014). Advanced, late successional ecosystem stages may not always be the target of restoration, as also early successional stages may exhibit a high conservation value for some specialized species (Řehounková et al. 2016; Tropek et al. 2015). Hence, their maintenance can also be a goal of restoration projects. Generally, it is easier to set targets to generalized plant community characteristics, such as total vegetation cover, and the presence of species functional groups than to species composition (Horáčková et al. 2015).
Conclusions and perspectives
In effort to restore the sites disturbed by mining and industrial activities, restoration projects should involve ecologically suitable and economically viable measures which will produce multiple social and ecological benefits. A challenge is that a general consensus of biodiversity indicators is difficult to reach due to the complexity of the biodiversity concept (Pitz et al. 2015). This may influence the restoration target, which is partially dependent on the values of the stakeholders. Besides the principally perceived negative environmental impacts of mining and industrial sites, post-mining and post-industrial sites are not only negative products of human disturbances. They may provide refugia for specialized wildlife (Prach et al. 2011; Heneberg et al. 2013; Mata et al. 2016; Řehounková et al. 2016; Tropek et al. 2015). Unless mining and other industrial activities destroy valuable sites with high natural, historical, or aesthetic value, they may increase, under certain conditions, biodiversity and geodiversity of a landscape. Some examples are given also in this special issue.
Spontaneous succession (passive restoration) per se often leads to the re-establishment of target ecosystem.
Natural processes can be assisted to speed up the recovery under adverse environmental conditions.
Adverse environmental conditions, contamination of the surroundings, or economic reasons may also favor technical reclamation.
Scientific information on various measures and approaches, and factors influencing the regeneration is a basis for the planning of effective ecological restoration at mining and post-industrial sites.