PLANT ECOLOGICAL PROBLEMS IN INCREASING THE PRODUCTIVITY OF 



ARID AREAS 



Dr H. Boyko.* 

 (Jerusalem) 



Approximately a third of the surface of the earth (Sears states 31%) is located in 

 arid zones, yet only a relatively small part of this area can be eliminated from this dis- 

 cussion on the basis of being climatically absolute desert. By far the largest parts of 

 the area can be classified as semi- deserts or man- made deserts. If we face the issue 

 of increasing productivity from the point of view of the plant ecologist, we must occupy 

 ourselves primarily with these regions. 



Among the tasks of ecology, pasture ecology occupies a position of major impor- 

 tance. I deliberately use the term 'pasture' in order to avoid use of the word 'grass- 

 lands', for it is precisely the steppe and prairie regions which constitute the second 

 boundary to the scope of any topic, both objectively and geographically. Though these 

 may also be in an arid region, they are nevertheless always covered by a dense blanket 

 of vegetation, alive or dead, even during the dry season. Between the areas completely 

 under vegetative cover and those of absolute desert which is climatically caused, lies 

 the main area subject to discussion here. Israel provides a very good example. Driv- 

 ing through this small country, we pass within several hours through the majority of the 

 global vegetative zones located in the Northern Hemisphere, namely the forest belt, the 

 steppe belt, the semi-desert belt, and the climatically- caused absolute desert. 



From the North - Mediterranean Laurel forest climax we pass through the Eu-\dedi- 

 terranean, semi- arid Quercetum cocciferae, and through the more arid sub -Mediterra- 

 nean forest association of Ceratonietum soliquae into that belt, which occurs globally 

 between the dense forest climax and the steppes, to which the above mentioned asso- 

 ciation is already a transition stage. This zone I call the arid border forest belt. In 

 south-west Asia it is divided into the Anatolian- Iranian Quercus Aegilops belt and the 

 Mauretanian- Iranian Pistacia mutica belt. These two intersect in Israel, from whence 

 they strike a wide arc round the Mesopotamian lowlands, the Pistacia further inland 

 than the oaks. Adjacent to this border forest belt is the Stipa steppe belt, followed by 

 semi-desert and desert. Analogous conditions occur all round the globe in both hemi- 

 spheres, with the possible exception of Australia. There we find a considerable amouni 

 of trees in a climatic zone where elsewhere we would expect only a treeless semi- 

 desert. 



This surprising phenomenon may indicate that in Australia tall, woody species 

 have had a much longer geological period in which to adapt themselves to drought resis 

 tance than is the case in other continents. In the steppe regions of south-west Asia 

 perennial herbs predominate, after grasses, as in the Anatolian steppe, then the tall 

 feather grasses gain dominance, the cover becomes ever sparser, the bunches are far- 

 ther apart, and we pass from steppe to semi-desert. Here woody plants, bushes, and 

 bushy perennials predominate, and between them there grow bunches of low grasses of 

 varying density. In the spring, depending on the rainfall of the preceeding weeks, 



• Chief Ecologist, Ministry of Agriculture and Development, Israel. 



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