Revegetation Dynamics of Cliff Faces in Abandoned Limestone Quarries

1. Revegetation dynamics on vertical cliff faces in abandoned limestone quarries were examined at 18 sites in southern Ontario, Canada. 2. A wide range of biotic and abiotic variables were measured in randomly positioned plots at each site. 3. Quarry walls ranged in age from 17 to 92 years since abandonment and this known chronosequence was used to investigate successional patterns in the vegetation. 4. Site age and the density of trees adjacent to the quarry walls had the strongest influence on vegetation community composition and abundance. 5. During the first 70 years of abandonment, species richness was high and variable. Community composition was also extremely variable during this period. 6. After 70 years, species richness on quarry walls dropped suddenly and the variation in vegetation composition was reduced. 7. This period of sudden change correlates with the growth of neighbouring trees on the quarry floor that start to shade the quarry walls at about 60 years since abandonment. 8. The final form of the vegetation community on the vertical cliffs in long-abandoned quarries is similar to the naturally occurring community on cliffs of the Niagara Escarpment. 9. The results of this study suggest that natural successional processes can be used to rehabilitate the vertical cliff faces that are produced in limestone quarry operations. 10. The benefits of allowing natural processes to rehabilitate the walls of abandoned limestone quarries are: the recruitment of an uncommon, but native component of biodiversity; a reduced initial cost; and a reduced long-term maintenance cost. 11. It is recommended that abandoned limestone quarries should not be rehabilitated by backfilling of exposed quarry walls.