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The Role of Competition as a Factor in Determining the Distribution of Dwarf Shrub Communities in the Mediterranean Territory of Israel
M. Litav, G. Kupernik and G. Orshan
Journal of Ecology
Vol. 51, No. 2 (Jul., 1963), pp. 467-480
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2257698
Page Count: 14
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1. The role of competition as a factor in determining the distribution of dwarf shrub communities in the Mediterranean territory of Israel was examined in field plots and in pot experiments. 2. Avena sterilis L., the most common annual, was found to strongly inhibit the development of the young seedlings of Poterium spinosum L., which is the most common among the dominant dwarf shrubs. 3. A very high mortality was observed among the competition-affected Poterium seedlings during the summer when Avena has already finished its life cycle. Competition-free seedlings, on the other hand, survived throughout the summer, adding appreciably to their dry weight. 4. Partial or total elimination of Avena during the experiments resulted in a better development of Poterium seedlings. 5. Irrigation and fertilization did not improve the development and survival of Poterium seedlings, sometimes supressing it even further. These treatments markedly increased the growth rate and final weight of Avena. 6. The strong competition effect of Avena on Poterium seedlings is in good agreement with the fact, known from field observations, that penetration of Poterium and many other dwarf shrubs into habitats supporting a rich annual vegetation is either retarded or prevented, while Poterium spinosum invades rapidly abandoned fields on soils unfavourable for annual vegetation. 7. It is suggested that in the past the distribution of dwarf shrub communities was restricted to sharply inclined slopes, rocky ledges and chalky soil supporting a poor annual vegetation. Their penetration into extensive areas after the destruction of the climax was a consequence of soil erosion with its resultant rock denudation as well as of a high grazing pressure, both processes acting mainly against the larger-sized annual species.
Journal of Ecology © 1963 British Ecological Society