Shrub clearance and livestock grazing benefits restoration of the flora in calcareous grasslands of Vercors Regional Park, Rhone-Alps, France
The conservation of dry calcareous grasslands in the French Prealps strongly depends on the maintenance of traditional low-intensity agro-pastoralism. The impact of current agro-pastoral practices on the conservation of the highly valued biodiversity of prealpine dry grasslands of south-eastern France was investigated during a six-year permanent plot survey in four sites with contrasting habitat conditions (mesic to xeric).The focus was to assess if a combination of shrub-clearing and grazing significantly affects species richness and floristic composition, especially species of conservation interest.
Study site: The study was undertaken in the limestone massif of the Vercors (Drôme and Isère districts), southwestern France. Four calcareous grasslands with contrasting habitat conditions (mesic to xeric) were chosen for restoration.
Experimental design: In each site, three permanent plots of 10 x 10 m located within dense shrubland patches were established in 1992. At each site, one plot had 25% initial shrub cover and two plots had 50% initial shrub cover.
Shrub clearance: Shrub clearing was undertaken manually between autumn 1992 and early spring 1993, in order to increase sward accessibility for livestock. Scrub was removed until a final cover of less than 5% was obtained. Cuttings were removed from the plots, stumps were left, so that some re-sprouting of shrubs (e.g. box Buxus sempervirens, broom Genista cinerea, sloe Prunus spinosa) occurred.
Grazing: Grazing management varied for each site, from mesic grasslands grazed by cattle at higher stocking rate (400 Livestock-Units (LU) days/ha to xeric grasslands grazed by a mixed flock of sheep and hardy goats at lower stocking rates (260 LU days/ha). Mesoxeric marly grasslands were grazed by either cattle (180 LU days/ha) or sheep (220 LU days/ha) at low stocking rates. The grazing season was from spring to autumn except at the driest site, which was from late summer to early winter.
Vegetation surveys: Vegetation was surveyed annually in late spring from 1992 (before shrub clearance) to 1997 with a permanent transect across the diagonal of each plot. Species frequency and percentage cover of bare ground was measured.
The scrub clearance and grazing had beneficial effects on the grassland flora. There was a strong increase in species richness and open grassland species frequencies four years after shrub-clearing; the average number of species was doubled 4 years after shrub-clearing for all sites.
Rare annuals and perennials of special conservation interest, re-established in barer patches created by the livestock grazing. At all four sites, there were similar positive trajectories of vegetation changes during restoration despite different habitat conditions and grazing regimes between sites.
The successful restoration of these alpine foothill calcareous grasslands was at least partially explained by the abundant availability of seed sources in adjacent grazed or mown grasslands.
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