The introduction of native plant species on industrial waste heaps: a test of immigration and other factors affecting primary succession.
Industrial waste heaps in NW England have become colonized by interesting floras which include regionally uncommon species. However, the range of species is restricted and the vegetation remains open even after 100 years. This appears to be due to the chemical and physical characteristics of the sites, and difficulties of immigration for appropriate species. To test these hypotheses and to explore the improvement of such areas for creative nature conservation and amenity, introduction of further native species was undertaken. Plant species from calcareous grassland were successfully established on alkaline chemical waste (17 out of 36 species introduced were permanently established) and blast furnace slag (21 out of 41 species introduced), and species from acidic heathland (10 out of 17 species introduced) were established on colliery shale. Some species were established on pulverized fuel ash, but the successful ones had no obvious characteristics in common. This demonstrated the limitations that can be set in isolated sites by problems of immigration. When suitably adapted species are introduced, appropriate niches for their establishment appear to be available. Failure of more nutrient demanding species showed that nutrient deficiency can also be a major factor controlling colonization. Factors affecting primary succession are discussed. They indicate the limitations faced by species which might require to migrate in the face of climatic or other environmental changes, and show that it is practicable to diversify the species composition of such derelict sites for creative conservation or amenity purposes.