A recent Forestry Commission report has indicated that there is some 6,000 hectares of damaged/derelict former industrial land in Wales (‘The Way Ahead for Welsh Forestry’, Forestry Commission). A UK Dept of the Environment report has also stated recently that there are 1900 hectares of current or ceased slate workings in the UK (‘Slate Waste Tips and Workings in Britain’, DOE, UK; Table 1). Planning permission has been granted for another 500 ha in the UK. Waste tips are found in Cornwall, Cumbria and the Highlands of Scotland but predominantly in North and Mid Wales. There are also extensive slate workings in France, Spain and Germany and general non-toxic mineral extraction sites in all EU countries. The total amount of slate waste in the UK alone has been estimated at 500 million tonnes with 6 million tonnes added each year. This is because, despite modern extraction and production techniques, 98% of quarried material is waste (usually tipped) and only 2% is saleable product.

Post-industrial land is an inevitable consequence of the extractive industry. Wales was at the forefront of the Industrial Revolution during the last century and it has many areas of derelict land dating from these activities. Currently active industries, particularly the extractive industries also create waste land, some of which, due to its location or topography, is unlikely to be used for other commercial, residential or productive activities and can therefore be restored. The restoration standards expected of mineral operators are increasing and there is an ever growing demand for technology development and guidance which will achieve these ends in the most cost-effective, environmentally friendly and socially acceptable manner. In the UK, the slate workings are predominantly in areas of extremely high landscape quality and in many areas quarrying has transformed the original landscape beyond recognition (e.g. Penrhyn Quarry).

Table 1. Summary of slate workings within the UK (source DOE, 1995)

Slate waste tips have been referred to as ‘temperate deserts’ because of their inability to support natural ‘unaided’ revegetation (DOE, 1995). Slate waste tips are generally much more resistant to natural colonization by vegetation than are most other forms of mineral extraction waste (e.g. coal spoils). This is due to the coarse particle size and extremely free drainage of slate waste, its resistance to weathering and the lack of plant nutrients. In addition, many sites are elevated and exposed, further limiting the rate of colonization. The slate waste is not contaminated by toxic chemicals and the environmental problems addressed by this project are more concerned with the physical rather than toxic problems of the substrate. On the positive side, abandoned slate workings provide breeding and roosting sites for birds, bats and other mammals and, with careful management, they can greatly enhance the biodiversity of an area. The majority of current slate-producing sites in Britain are still extracting and surface tipping on land with little or no planning for restoration while approximately 10% of the areas are abandoned (Table 1). These disused slate waste tips also present environmental hazards in that they frequently include unguarded quarry faces, deteriorating structures and unstable tip retaining walls.

Many slate workings are located within or next to National Parks, Areas of Outstanding National Beauty and Sites of Special Scientific Interest (SSSI). The visual impact of these workings can be significant despite the relatively small areas involved. Perceptions of slate workings and especially the waste tips range from an unacceptable disfigurement of otherwise beautiful landscapes with high touristic value, to an essential component of the cultural heritage of communities which only exist because of the slate industry. The restoration of slate workings will therefore require maintaining a balanced approach to these perceptions, seeking to reduce the negative impacts of workings without reducing their historical interest. Another important social factor is the apparent expectations of the general public in restoration schemes of this nature. Specifically, this refers to their apparent desire for an ‘instant landscape’ and for ‘rapid greening’ to take place. This rapid greening, however, is frequently followed by rapid deterioration and restoration failure (see below for more details).

Due to the cost of transport and the sheer volume of slate waste (500 million tonnes in the UK), its use as a ‘secondary’ mineral has been constrained. At present, the removal of slate waste is insignificant in relation to the volume being generated or the size of the existing waste tips and it is unlikely that this situation will alter in the near future. The most practical solution to this problem (and that of other non-toxic mineral workings) therefore relies on the reclamation and restoration of the site with the ultimate aim of recreating a natural landscape with high biodiversity and amenity value. The history of many slate extraction sites shows that it is unrealistic to expect the rapid natural (unaided) development of high biodiversity vegetation. Indeed, this is evidenced by the very minimal unaided regeneration which has occurred at many of the sites over the last 150 years. The main study area at Penrhyn Quarry still remains a ‘temperate desert’ with very little natural regeneration. The aim of this project is to demonstrate a method to accelerate natural regeneration and secondary successional processes such that a sustainable semi-natural vegetation of high biodiversity, conservation and amenity value can be achieved within a cost effective framework and achievable life span. The two types of habitats which we wish to recreate are Dry Heath and Mixed Deciduous Woodland. The techniques employed to achieve this will include; the use of genetic material of local provenance, cell planting strategies and substrate ameliorative techniques including the use of synthetic water retaining polyacrylamide gel polymers.

Previous attempts at restoring slate quarries have largely been unsuccessful in either achieving or maintaining a landscape of high biodiversity value (DOE, 1995). In addition, past attempts to recreate habitats akin to the surrounding environment have been even more limited as highlighted by the 1995 DOE report which states ‘….there has been a lack of concern generally for the conservation of features which today would be regarded as valuable’. The reason for these failures mainly relates to the use of inappropriate plant genetic material, an inadequate knowledge of the constraints imposed by the planting substrate and a lack of awareness of the environmental constraints. In addition, these schemes are frequently extremely expensive costing on average about £65,000 ha^-1 to restore (based on these figures, the total cost of restoring all slate waste tips in the UK alone would be £120 million [169 million ECU]). Practical, more cost effective schemes are therefore required to restore slate waste.

Typically, restoration of many mineral extraction sites and municipal waste sites has involved the spreading of a thin layer of topsoil over the site upon which grass is planted and fertilizers applied. Unfortunately, this technology cannot be applied to slate wastes as has been demonstrated in a number of trials of this nature on other slate waste quarries in the UK (DOE, 1995). Firstly, due to the porous nature of the substrate, the topsoil is frequently washed away leaving the plants exposed and vulnerable to drought and nutrient stress. In addition, the types of grass planted are frequently inappropriate for an upland exposed climate and are prone to extreme grazing pressure (oases of green attracting herbivores from km around). In addition, the supplementing of the soil with inorganic fertilizers or broiler litter suppresses the development of nitrogen fixing plants such as clover which are essential for the long term sustainability and also selects plants capable of responding to high nutrient levels which subsequently die after nutrient exhaustion. Further, the N and P fertilizers can be rapidly leached in high rainfall areas leading to pollution and loss of biodiversity in local water courses. The failure of these vulnerable swards illustrates the need to match the land use objectives and the selection of species with the resources available for management. A restoration project can only be successful if the vegetation which is established is sustainable under the environmental conditions and the conditions of use and maintenance which follow the initial scheme.