On heath pasture in Montseny Biosphere Reserve and Natural Park (northeast Spain), replacement of traditional burning by shrub harvesting has led to encroachment onto dry Festuca-Agrostis grasslands of conservation value, by besom heath Erica scoparia (a common ericaceous shrub in the region). A study was undertaken to describe population dynamics (e.g. recruitment, mortality and growth rates of seedlings) of E. scoparia, and to assess if continuation of traditional sheep and goat grazing can control ericaceous shrub spread.
At two study sites on La Cortada estate dominated by E. scoparia and heather Calluna vulgaris, intermixed with grassland patches, 64 (1 m²) quadrats per site, were arranged (1 to 4 m from the heath edge) to determine ericaceous shrub colonisation patterns.
Burning of small patches (several hectares) of shrubs on an approximately 10 year rotation was undertaken until the area was declared a Natural Park in 1977 and a Biosphere Reserve in 1978. Subsequently E. scoparia has been harvested (cut near ground level) on an 8-10 year rotation.
Moderate intensity grazing by a flock of sheep (200 individuals) and goats (70) equivalent to a stocking rate of about 2.8 animals/ha has continued.
From spring 2001 to spring 2003, vegetation censuses were undertaken.
After cutting, E. scoparia vigorously re-grows, reaching a canopy cover equivalent to pre-cutting levels after 3-4 years, resulting in dense homogeneous E. scoparia stands. E. scoparia seedlings were most abundant nearest the heath edge, density declining to the grassland interior. Seedling density was highest when grass cover ranged between 10 and 50%, above 50% grass cover, E. scoparia seedling density was greatly reduced.
Sheep did not eat E. scoparia and goats only occasionally so. Although 12% of E. scoparia stems showed signs of trampling damage, this did not inhibit colonisation.
C. vulgaris was common in the shrubland (16% cover) but seedlings (highly palatable to sheep and goats) were almost absent in the grassland patches.
The results indicate that current grazing and E. scoparia harvesting regimes are not effective in preventing E. scoparia encroachment.
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