years aridity had definitely increased in the eastern part of Cape Province and Nor- 

 thern Transvaal following the removal of evergreen forest. Although it could not be 

 proved that tree planting increased the rainfall or that forest clearance reduced it, 

 the availability of water was certainly increased by the presence of trees. 



Commenting on Professor Stebbing's remarks, Dr A. S. Thomas said that a deep 

 humus layer was seldom to be found in tropical forest: indeed there was usually 

 more organic matter in grassland soils. He did not believe that fire had a dele- 

 terious effect on grassland - the worst factor was compacting of the soil surface by 

 stock animals. Tramping had produced desert -like conditions in Karamoza where 

 there was an annual rainfall of 25 inches. When tse-tse fly invaded the land how- 

 ever, and the stock went away, the vegetation soon recovered. He agreed with Pro- 

 fessor Phillips that tse-tse had a beneficial effect in preserving Africa. 



Fire was a useful agent in the right place and at the right time, provided that 

 the ground was allowed to rest afterwards, said Professor Phillips: and much had 

 been learned about mechanized agriculture from experience in Tanganyika. The 

 removal of deciduous scrub at Kongwa had not resulted in a 'dust- bowl* or 'tennis 

 court'; and acres thrown back to nature had produced a crop of grass at the end of 

 a year. Africa needed a few years to rehabilitate herself he suggested. 



The impossibility of countering the rape of the earth by overgrazing, when the 

 entire population was clamouring for food, was mentioned by another speaker with 

 experience of the problems in Somaliland Protectorate. 



The paper by Professor H. C. Trumble and Mr K. Woodruffe was presented by 

 Professor J. A. Prescott, F.R.S. in the absence of the authors. In a short introduc- 

 tion, the latter said that the University of Adelaide possessed two field stations in 

 the semi- arid fringe to the southern margin of the Australian desert. Koonamore 

 dealt with the natural regeneration of native shrub steppe and was in charge of the 

 School of Botany. Yudnapinna had been endowed since 1938 for the special study 

 of pastoral management in this environment and was the responsibility of the Waite 

 Agricultural Research Institute. There had been pastoral occupation in the regions 

 for nearly one hundred years, and overstocking with sheep during drought periods 

 had resulted in an estimated loss of 80% of the original perennial shrubs. It was 

 expected that these studies by the Waite Institute would lead to a basis for the es- 

 tablishment of scientific principles of pastoral husbandry. 



In the discussion following the paper, Dr H. Boyko enquired about competition 

 between bushes and grasses in areas where Atriplex and Kochia were the dominant 

 plants. This was a subject of very great importance in large areas of North Ameri- 

 ca. North Africa and South-west Asia. In North America Artemisia tridentata cov- 

 ered large areas as a result of overgrazing. He had recently seen large scale ex- 

 periments from Montana to Texas that were designed to establish methods for con- 

 trolling this undesirable shrub. In North Africa and South-west Asia, a related 

 species A, herba alba covered nearly the whole area between the isohyetals of 200 

 and 400 mm. from Morocco to Afghanistan where there were cool winters. The latter 



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