Experiments on the effects of fertilizer and rabbit grazing treatments upon the vegetation of a limestone quarry floor

Published source details Davis B.N.K., Lakhani K.H. & Brown M.C. (1993) Experiments on the effects of fertilizer and rabbit grazing treatments upon the vegetation of a limestone quarry floor. Journal of Applied Ecology, 30, 615-628.
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Summary

Abandoned limestone quarries in Britain can develop vegetation communities of high conservation interest as they may support many local and rare species. However, low seed inputs, low nutrient levels and grazing by rabbits Oryctolagus cuniculus have all been cited as factors constraining colonization by plants. This study describes the effects of two very low levels of fertilizer application and three levels of rabbit grazing treatments that were used to accelerate the colonization of a limestone quarry floor from an initial average vegetation cover of 21%.

Study site: The study was carried out at Clipsham Old Quarry (National Grid ref: SK 980152) in Leicestershire, eastern England. Limestone quarrying here ended in 1941 producing a pit about 160 m long by 40-80 m wide. A sparse vegetation had since developed, with surrounding banks of clay overburden well vegetated with tor grass Brachypodium pinnatum and yellow oat-grass Trisetum flavescens (UK National Vegetation Classification CG4 black knapweed Centaurea nigra- rough hawkbit Leontodon hispidus subcommunity, Rodwell 1992). The quarry was suurounded by a mix of arableland, ley grassland, active quarry workings and woodland. There was a well established rabbit population, and fallow deer Cervus dama were present (tracks recorded).

Experimental design and treatments: The area selected was a sparse, herb-dominated community with 70-85% bare ground, with friable material (broken limestone rubble etc.) to about 15 cm in depth. In 1980 a 13 x 11.5 m area was marked out with nails and string and divided into six blocks each containing six plots. The plots were divided into two 1 m² split-plots. All blocks and plots had a 50 cm wide buffer zone.

Treatments were:

i) Summer caging - covering plots with wire mesh cages to exclude rabbits and deer during the growing season (April-September inclusive);

ii) Year-round caging - covering plots with cages to exclude rabbits during the whole year;

iii) Fertilizer – adding fertilizer in spring (26 March 1981: N 0.7; P 0.7; K 0.35; Mg 0.35 g/m². 1 April 1982: N 1.2; P 1.8; K 1.6; Mg 1.0 g/m²);

iv) Control plots – no caging, no fertilizer addition;

From 1983 onwards an 'extra-fertilizer' treatment was added by splitting the plots (17 May 1983: N 2.5; P 1.35; K 1.2; Mg 0.75 g/m². 2 April 1984: N 2.5; P 0.9; K 1.6 g/m²).

All treatment combinations were studied over 5 years for their effects upon the percentage cover of vegetation, species richness, species frequency and the number of species in flower.

There was virtually no change in average percentage vegetation cover in the control plots (no fertilizer, unrestricted grazing), but all the other treatments produced some increase. This was especially evident with all-year protection from grazing with an increase to 52% recoded, and with combinations of protection plus fertilizers (increases to 35-84%).

There was a gradual increase in species richness over the whole experimental area during this period from 34/m² to 39/m², but the effects of particular treatment combinations were less distinct. Species frequency within plots increased significantly under 8 of the 12 treatments. Highest values resulted from double fertilizer applications with or without protection from summer grazing by rabbits and deer. The double fertilizer combination also gave the greatest number of species in flower (average 11.1/m²), whilst all year caging with no fertilizer (6.8/m²) and controls (6.4/m²) had the fewest species in flower.

Conclusions: Vegetation monitoring showed that there was little or no discernible change in vegetation cover over 4 years in control plots. The authors consider that natural succession to a closed sward under present conditions would probably depend on slow atmospheric deposition of nutrients and from N-fixation by two legumes, bird’s-foot trefoil Lotus corniculatus and black medick Medicago lupulina present in the quarry. Artificial addition of very small amounts of fertilizer as undertaken in this experiment, coupled with protection from rabbit grazing greatly enhanced vegetation cover and encouraged flowering.

References
Rodwell J.S. (Ed.) (1992) British Plant Communities 3. Grasslands and Montane Communities. Cambridge University Press, Cambridge, UK.

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