FORESTS, ARIDITY AND DESERTS. 



Professor E.P. Stebbing 

 (Edinburgh) 



The Man-made desert is a stern reality which so far has rarely been faced up to. 

 Man has been the enemy of the forest and of vegetation ever since he learnt to grow 

 crops for food and to pasture flocks and herds on the countryside. The term erosion is 

 widely used but very often without a real understanding of what is meant. It is easy 

 for the public to understand one type when they see a raging torrent tearing out the 

 heart of a hillside. But there are several different types of erosion which in the end 

 may result in the same catastrophe, namely the production of desert or arid conditions, 

 the methods being different. 



I propose to confine myself here to one of the commonest and probably the oldest 

 of the types resulting purely from the acts of man. The most ancient type of cultivation 

 known to man is in nature and mainly covered with forest, being known in English by the 

 name of shifting cultivation. This type of cultivation from its very origin has many dif- 

 ferent names, even in the one country. For example in India there was a different name 

 for it in N. India, the Central Provinces, Bengal, Assam, Madras, Burma and Ceylon. In 

 Europe in olden times the same variation in nomenclature existed. But the method was 

 normally the same. A small piece of forest out of the surrounding mass was felled, the 

 material as soon as dry enough fired, and the ashes roughly spread over the ground thus 

 opened out and the seed of a crop sown. At the end of a few years, roughly three to 

 five, a dense weed growth supervened, or the soil decreased in fertility, or both. The 

 shifting cultivator then moved and repeated the operation in another piece of the forest. 

 When the world was young and the population small the forest was the enemy and to ob- 

 tain pasturage for increasing flocks the forest was fired to get rid of it. It was the in- 

 crease in population that gradually and imperceptibly had its effect on the forest. In 

 the temperate parts of the world and especially in the case of the conifers, great forests 

 were swept away. In the tropical and sub- tropical forests, however, where the forests 

 consisted of broad- leaved trees of many species intermixed, the forest did not neces- 

 sarily disappear but suffered a slow degradation. Valuable timber species susceptible 

 to fire disappeared but the forest remained. The habit of setting fire to the felled 

 material on the area to be cultivated resulted in other fires spreading into the surroun- 

 ding forest and the countryside during the hot season. This danger and damage is only 

 too well known to the modern day forester. The eventual degradation of the forest from 

 a fine dense high forest to a scrub, variously denoted scrub, bush or savannah, took 

 thousands of years and was in effect so imperceptible that it had passed unperceived — 

 in fact was lost in the past histories of the earlier nations who lived in what are now 

 deserts. Wars helped in this disappearance with the habit of a retreating army of set- 

 ting fire to the countryside to prevent pursuit. Sites of these old time nations are 

 known to us. It is suggested here that it was this degradation of the forests and the 

 drying up of the water supplies which led, in more than one instance, to the final dis- 

 appearance of the peoples. Time does not allow me to mention such instances. In many 

 parts of the world the shifting cultivator was therefore, to a certain extent nomadic. In 



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