Traditionally, ancient polder embankments (about 500 km in total length) in the Zak van Zuid-Beveland, Zeeland province (Netherlands) were sheep-grazed, but this ended in 1959. Tall herbs increased, some areas became invaded by shrub and overall plant species diversity decreased. In order to maintain herb-rich grassland flora, in 1980 sheep grazing was reinstated on 50 km of embankment. Other management included mowing and cattle-grazing, and some stretches were burned regularly. In 1986, vegetation was compared with that of 1972 to evaluate the effect of the various management practices (and no management), in particular sheep grazing.
In 1972, 84 sample plots (mostly 5 x 5 m) were established and vegetation recorded (Braun-Blanquet method). Surveys were repeated in 1986. Various topographical/environmental parameters that might effect vegetation development were recorded. There were 11 main management practices considered:
1) early July mowing and hay removal;
2) October mowing and hay removal;
3) light sheep grazing (<8 hour/month/500 m of embankment with about 200 sheep);
4) moderate sheep grazing (8-11 h/month/500 m);
5) fairly intensive sheep grazing (11-15 h/month per 500m);
6) intensive sheep grazing (>15h/month/500m);
7) light cattle grazing;
8) summer mowing and hay removal, light aftermath sheep grazing;
9) annual late winter burning;
10) irregular management, i.e. a mix of uncontrolled management including mowing, burning, grazing, herbicides etc;
11) no management.
Due to the scale and variation in embankment characteristics and management practices investigated, embankment vegetation developed in many directions. However, changes in species composition and structure were clearly related to management. In general, moderate to intensive sheep grazing achieved the best improvements to, or maintenance of, the conservation value of the embankment floras.
Irregular management, light grazing, mowing late in the season and burning, were generally less effective with ruderal species dominating and development of species-poor fragmented grassland communities.
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