Individual study: The effect of sheep-grazing, phosphate addition and stone cover on productivity of Mediterranean grassland at Tel Hadya, Syria
Pagnotta M.A., Snaydon R.W. & Cocks P.S. (1997) The effects of environmental factors on components and attributes of a Mediterranean grassland. Journal of Applied Ecology, 34, 29-42
As a consequence of historic and contemporary overgrazing, many west Asian grasslands are severely degraded. The situation is particularly acute in parts of Syria. This 2-year study looked at various environmental factors influencing abundance and seed production of various plant species in a Syrian grassland, and assessed if exclusion of sheep promoted vegetation recovery.
Study area: The study was undertaken at Tel Hadya (headquarters of the International Center for Agricultural Research in the Dry Areas – ICARDA), 30 km south of Aleppo city (36º01’N, 36º56’E). The area comprised natural legume- and grass-rich pasture (127 species recorded, mostly annuals, including 56 legumes and 21 grasses). The most common legumes were woolly clover Trifolium tomentosum, starry clover T.stellatum and field clover T.campestre, most common grasses were three oat-grass Avena and three brome Bromus species.
Six treatments applied to experimental plots:
i) pre-existing conditions (control);
ii) phosphate added (0 or 25 kg/ha P2O5);
iii) low (0.8) or high grazing intensity (1.7 sheep/ha);
iv) pre-existing stone cover (low or high);
v) amended stone cover (addition or removal of stones to 20 or 80% stone cover);
vi) protected or not protected from grazing.
Measurements: At various times during the two growing seasons (1988-89 and 1989-90) the following were recorded: biomass, yield (harvested at the end of each growing season), seed bank (at the end of 1989-90 season), stone weight and volume, bare soil and ground cover, plant density, number of flowers, flowering time and seed size. Chemical analysis of various soil properties (available phosphorous, total nitrogen, organic matter, calcium carbonate and pH) was also undertaken.
Initial growing conditions (a measured by biomass) most affected subsequent plant performance, although less so in year 2. Organic matter, nitrogen and soil depth were all greatest where initial biomass was highest. In areas with greater pre-existing stone cover, growth was reduced (probably because greater stone cover was associated with shallower soils and lower soil fertility). However, experimental addition of stones increased productivity, probably as they protected vegetation from sheep grazing.
The higher sheep stocking rate clearly reduced biomass production of most plant species (M. coronata and T. tomentosum however increased, probably due to their prostrate growth habit), whilst phosphate addition increased it. Protection from sheep-grazing led to increased plant cover with improved performance of most species, but different species responded in different ways.
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