Individual study: Effect of protection and controlled grazing on the vegetation of a Mediterranean desert ecosystem near the village of Omayed, northern Egypt
Ayyad M.A. & H. F. El-Kadi (1982) Effect of protection and controlled grazing on the vegetation of a Mediterranean desert ecosystem in Northern Egypt. Vegetatio (now Plant Ecology). Plant Ecology, 129-139
The Mediterranean desert of Egypt is an arid region with a long history of intensive land use, mainly grazing and rain-fed farming. Over-exploitation, coupled with a severe environment and uncertainty of rainfall, has resulted in land degradation and desertification. The present study provides preliminary assessments of the effect of i) protection of areas of land from livestock grazing and ii) controlled grazing, on the vegetation composition and phytomass in a Mediterranean desert ecosystem in northern Egypt.
Study area: The study was conducted near the village of Omayed, 12 km south of the sea coast (29º12'15"E, 30º45'45"N) about 80 km west of the city of Alexandria, northern Egypt. The study was carried out in a 1 x 1 kmÂ² plot in a large non-saline depression (45-75 m altitude). The soils are generally sandy and often compact at depths below 25 cm. The vegetation in the study area generally belongs to the Plantagineto-Asphodeletum microcarpae association (Thymelaeion hirsutae alliance)
The area has a rainy season (mainly October and November) with a average annual rainfall of 150 mm. Monthly average temperature varies between 13ºC in January and 26ºC in August. During the period of investigation (August 1977 to July 1979) temperatures were about normal, but rainfall was low: about 55 mm in the 1977-1978 season (falling mainly in December and January) and about 76 mm in the 1978-1979 season (mainly in November and December).
Study plots: Four plots of 175 x 800 m and one (plot 4 treatment, see below) of 70 x 800 m were established. Treatment applied were:
Plot 1 - fenced in July 1974, from May 1977 subjected to 50% of the grazing intensity practiced in the surroundings;
Plot 2 - fenced in 1977 and subjected to 50% of the free grazing intensity since May 1977;
Plot 3 - fenced in 1977 and subjected to 25% of the free grazing intensity since May 1977;
Plot 4 - fenced in July 1974 with no grazing until the end of the study;
Plot 5 - an area outside the fence with free grazing, c.6 heads/10 ha.
Grazing was presumably by sheep or goats (as 'flock size' mentioned) but not specified in original paper.
Changes in density, cover, frequency, phytomass and the phenological sequence of species were recorded and compared to those of the same species outside the fenced plots.
Density and cover of perennials, frequency and presence of annuals, and total phytomass increased as a result of protection and controlled grazing. Data analysis indicated that the distribution of plant species in the study area was more related to overgrazing than to other important factors, such as rainfall.
Outside the fenced area: The total density of the vegetation outside the fenced area decreased by >15% (mainly due to decrease in two perennial herbs, Asphodelus microcarpus by >20% and Plantago albicans by >33%) from 1974 to 1979, while total cover increased by about 38% due mainly to perennial shrubs, and succulents: Thyrnelaea hirsuta (44%) and Anabasis articulata (c.75%).
No grazing: In the fenced plot with no grazing since 1974, total density increased by about 105% (due mainly to increases in the perennial herbs: Carduncellus sp. (c.96%) and P.albicans (c.465%), and the perennial shrubs: Echiochilon fruticosurn (c.100%) and Helianthemurn lippii (618 %). Total cover increased by about 137%, again mainly due to Carduncellus sp. (c.96%), P.albicans (c.465%), E.fruticosurn (c.100%) and H.lippii (618 %). Two species, Artemisia monosperma and Launaea resedifolia hardly evident in 1974, contributed greatly to the increase in density (c.17 of the total percentage) and cover (c.21 of the total percentage).
50% of free grazing intensity: In the 50% of free grazing plot, the increase in density and cover by 1979 was even greater than in the no grazing plot. In the plot fenced in 1974, and subject to controlled grazing since 1977, total density increased by 138% and total cover by 172%. In the plot fenced in 1977, the increases were 249% for total density and 138% for total cover. (The 25% of free grazing intensity is not discussed in the original paper).
Conclusions: The study indicates that no or reduced livestock grazing intensity for five years resulted in remarkable increases in density and cover of perennials, and in frequency and presence of annuals. That the increases are mainly due to reduced or no grazing, and not to variations in rainfall, is indicated by the small relative changes that occurred outside the exclosure. Whilst, it may be imprudent to draw firm conclusions from this short-term experiment as the effects of the inconsistency of rainfall and the degree of degradation may surpass the effect of protection over only a few years, it is clear from these results that to instigate vegetation recovery requires relief from heavy grazing.
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