Individual study: The effect of mowing regimes on the bryophyte layer in a calcareous grassland, Nismes, Hainaut, Belgium
Vanderpoorten A., Delescaille L.M. & Jacquemart A.L. (2004) The bryophyte layer in a calcareous grassland after a decade of contrasting mowing regimes. Biological Conservation, 117, 11-18
Calcareous grasslands are a semi-natural habitat with high biological value. In Europe, much grassland has been lost due to conversion to arable, and reduction of grazing in many areas has led to further declines as they succeed to woodland. Consequently, many calcareous grasslands are now managed in nature reserves, and the emphasis has been placed on maintaining vascular floral diversity. However, other taxa such as bryophytes and lichens, which contain a number of rare species restricted to this habitat, have been largely ignored by management strategies. In this study, the effect of different mowing regimes on the bryophyte community of a calcareous grassland is investigated.
Study site: The effect of different mowing regimes on the bryophyte community of a calcareous grassland was investigated in calcareous grassland nature reserve at Nismes, Belgium. The reserve is situated on a flat top hill of Devonian limestone, at an altitude of 225 m.a.s.l. The study area within the reserve is 175 x 50 m in area, and surrounded by oak Quercus and pine Pinus plantations. The area comprised tor grass Brachypodium pinnatum dominated grassland, with sparsely scattered shrubs (sloe Prunus spinosa) and small trees (oak and pine).
Mowing regimes: In the winter 1988/9, the invading shrubs and trees were cut. Plots of two sizes were delineated, six larger 100 m² plots, and smaller 30 x 80 m plots homogenous in topography and vegetation. Over the following years (1989-2002), parts of the grassland was mowed following one of two mowing regimes, or left unmown. The three mowing regimes were applied, two plots each:
1) Once a year outside the growing season (in March or October)
2) Once a year in the growing season (in May or July)
3) Non-mowed control
In mowed plots, litter was raked from the inside of the plot to the outside.
Vegetation survey: In each 100 m² plot, ten 1 m² quadrats were studied along a 10 m long transect. In each quadrat, species cover was recorded as follows: 0.25 for an individual shoot; 0.50 for two to several shoots with <1% cover; 2.5 for cover between 1 and 4.9%; 15 for cover between 5 and 24.9%; 37.5 for cover between 25 and 49.9%; 62.5 for cover between 50 and 74.9%; 85 for cover between 75 and 94.9%; and 97.5% for cover between 95 and 100%. Bryophytes surveys were conducted in March and April 2002.
Number of bryophytes: The average number of bryophyte species per quadrat did not differ significantly depending on mowing regime. Plots mowed outside of the growing season had 7.5 species/quadrat, plots mowed in the growing season had 7.1 species/quadrat, and control plots had 5.8 species/quadrat. Additionally, of the eleven bryophyte species recorded in the study, all species were recorded (at least once) in plots mowed outside the growing season, and ten species were recorded in plots mowed in the growth season and in control plots.
Bryophyte cover: Average cover of each bryophyte species did not differ between the three regimes, except for Scleropodium purum which reached about 80% in mowed plots compared to 25% in control plots and Plagiomnium affine which exhibited the reverse trend with significantly more in control plots (1%), compared to plots mowed outside (<1%) and in (0%) the growing season.
Conclusions: As a mangement technique, mowing and removal of the cut vegetation proved ineffective in promoting growth of many annual bryophytes (several species of which are of high conservation concern), as mowing promoted a continuous dense sward cover of herbs, grasses and mosses. This afforded little opportunity for establishment of annual bryophytes. The authors (from previous experience) suggest that grazing should be considered the best management strategy for promoting bryophyte growth as this, and the associated disturbance, results in a less homogeneous sward cover which creates suitable more-open patches which facilitates the growth of annuals.
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