Paul Richardson and Shannon Tomlinson, graduate students of Dr. Doug Larson (with the Cliff Ecology Research Group at the University of Guelph), began work in 2003 to evaluate whether limestone quarries could be restored to a target habitat known as alvar. Alvars are globally imperiled ecosystems; hence answering this question could have benefits both to the conservation of alvars and the restoration of abandoned quarries. At abandoned quarry sites across southern Ontario the species composition of vascular vegetation, bryophytes and lichens, and the composition of the seedbank were determined and compared to information collected at alvar sites. An experimental study evaluating constraints of spontaneous succession to alvar was also begun.

Researchers from the University of Guelph identify the vegetation that has established on abandoned quarry floors to test the idea that alvar creation may be a suitable restoration target for quarry rehabilitation

Alvars are characterized by thin, patchy soil cover overlying limestone bedrock. However, these thin soils support a tremendous diversity of plant life including grasses, flowering plants, mosses, lichens and algae.

Two research questions were posed:

(1) To what degree are abandoned limestone quarries similar to alvars in their ecological structure?

(2) What factors limit the ability of alvar species to colonize abandoned quarry floors?

Question (1) was answered by a two-pronged approach. First, 13 abandoned quarries were sampled for their existing vegetation and environmental features. An analysis was carried out that characterized each site and examined the differences among sites. Next, the quarry floor biophysical environment was compared to the naturally occurring biophysical environment on 7 alvars. Question (2) was answered by carrying out manipulative work in 4 abandoned quarry sites. In a field experiment, plots were seeded with alvar and quarry floor species, and also provided soil amendments such as silica sand addition, organic carbon addition, competition removal and nutrient addition.

It was discovered that the individual quarry floors were quite variable in terms of species composition, but less so in terms of the physical environment. Despite this variability, quarry floors and alvars were strikingly similar. Seventy-seven of the 246 species of vascular plants, bryophytes, and lichens found on quarry floors are also found on alvars, and 24 of the 200 vascular plant species, or 12%, are 'characteristic' of alvars (meaning they are found on more than half of the alvars in Ontario). Comparatively, natural alvar surveys show they support a community composition with 20-25% of plant species ‘characteristic’ of alvars. Quarry floors are much more similar to naturally occurring alvars than was expected, with natural processes responsible for roughly a 50-60% conversion of quarry to alvar in terms of species composition. Strong evidence was found for seed limitation as the principal factor limiting the colonization of quarry floors by alvar species.

In the manipulative experiment, the establishment of both quarry and alvar species was similar, and soil amendments or other treatments had very minimal effects, though silica sand addition increased species establishment success, and nitrogen fertilization decreased establishment. In addition to the results from the planned research, the catastrophic drought in the early summer of 2005 provided even better information regarding the suitability of alvar as restoration target for abandoned quarries. Over the summer the rainfall was the lowest on record in 57 years. Despite the severity of the drought, survival of plants that were established on the quarry floors was high, with planted alvar species having even higher survival rates than the resident and planted quarry floor species. Another interesting result was that the persistence of the community of plants was found to increase with increasing species richness. Plots that had greater species diversity better survived the drought conditions.

In summary, abandoned limestone quarry floors in Ontario are more structurally and functionally similar to alvar ecosystems than has been appreciated before. Natural processes have taken control of soil development and species recruitment, leading to ecosystems that have moved about halfway to becoming legitimate alvars.
A more rapid development of quarry floors into these real alvars seems to require nothing more than seed and silica sand addition.

On the basis of the work done in this project, four steps will accomplish the restoration and management of abandoned limestone quarries to new alvar habitat:

(1) Bring in alvar seeds.

While the whole array of alvar species was not tested in this work, we predict that the broader the array of alvar species used in plantings, the greater the chance that the quarries can be used to extend the range of alvar endemics. Seed of alvar plants should be collected and/or grown by experienced people and we have approached the Royal Botanical Gardens to establish a collaborative program to that end. Success of planted species should be monitored at each site, and the range of 'best performers' should be expanded at each site. An emphasis should be placed on making as diverse a planting as possible. All seeding should take place in spring. Sites undergoing restoration using alvar species should, if the populations take hold adequately, also be used as seed sources for additional plantings.

(2) Do not removing existing vegetation or soil.

The existing vegetation should not in any way be removed or interfered with. Operators need not worry about the plants already growing on the quarry floor. Even the weedy plants have had a rock outcrop origin and hence may contribute to the stability of the site. Soil amendments are largely unnecessary on sites older than 10 years. If a newly abandoned quarry is to be rehabilitated, a mixture of sand and compost will add nutrients, fines and carbon. Amended soil depth in vegetated areas should not exceed 2 cm. The existing soil should not be tampered with. Do not fertilize - especially with nitrogen.

(3) Increase spatial heterogeneity and reduce disturbance.

Spatial heterogeneity (crevices, fractures, rock piles, etc.) should be manufactured at small and large scales. The use of rocky debris to create different microsites will provide greater habitat diversity, encourage soil development and aid in trapping seeds and retaining moisture. Human traffic should be discouraged to reduce mortality due to trampling. Once the vegetation has established and human traffic is lessened, other species may colonize more rapidly. This may be especially important for herptiles and birds. Signage should be posted to indicate that former quarry sites rehabilitated in this fashion are nature preserves.

(4) Monitor and report on your restoration results.

Records of the restoration work should be kept and successes or failures communicated to other property owners. This will form the basis of adaptive management in the future. Quarry operators should advertise restoration activities in order to derive appropriate credit for their work.

Be sure to communicate that the success of the restoration not be judged by percent vegetation cover, since open rock is itself a feature of alvars.