446 



NATURE 



[August 2, 19 17 



opinion that an investigation of the influence of 

 forests on rainfall would be very difficult and un- 

 likely to lead to any definite result. Nevertheless, 

 the Government of India sent out to all the local 

 Governments a request that the subject should be 

 inquired into and all available information col- 

 lected. In due time the local Governments sent 

 in reports on their owrr provinces, and these are 

 tersely summarised by Mr. Hill. with an admir- 

 able neutrality, which nevertheless fails to conceal 

 the fact that the reports differed widely in quality. 

 The general result is stated officially as follows : — 



"After a careful examination of the replies re- 

 ceived from local Governments, as summarised 

 above, and after consultation with the Director- 

 General of Observatories, the conclusions arrived 

 at by the Government of India were briefly that 

 the influence of forest on rainfall was probably 

 small, but that the denudation of the soil, owing 

 to the destruction of forests, might, as far as 

 India is concerned, be looked upon as an estab- 

 lished fact ; while as regards the effect of forest 

 preservation on rainfall and the underground 

 water supply, the papers forwarded did not pro- 

 vide sufficient information to justify any change 

 in the principles on which the forest policy of the 

 Government has hitherto been based. It was re- 

 marked that these principles were founded mainly 

 on considerations of a directly economic character, 

 connected with the conservation of the grazing 

 resources and forest produce of the country, and 

 that the climatological considerations did not in 

 any way affect these well-established principles." 

 The Government of India forthwith sent a second 

 series of questions to the local Governments with 

 the view of ascertaining whether experiments might 

 not be instituted in order to obtain fresh data. 

 These dealt with the local differences within and 

 without forest areas in rainfall, soil water level, 

 and height and duration of floods. The local 

 Governments duly prepared and sent in reports, 

 which were considered by the Government of India 

 in consultation with the Board of Scientific Advice, 

 and the final decision, expressed in five para- 

 graphs, may be summarised thus : — (i) Meteoro- 

 logical stations in specially selected positions in- 

 side and outside forest areas would probably yield 

 valuable results, and "if it be found possible .to 

 initiate inquiries of this nature further action would 

 be taken." (2) Observations on soil water level 

 need not be initiated, as the data would be of little 

 value in showing forest influence. (3) Satisfactory 

 experiments on floods could not easily be under- 

 taken, but the belief that forests are beneficial in 

 this respect is confident and almost universal. 

 (4) No material change in the forest area of any 

 province seemed to be contemplated, but if such 

 changes should be made the Government of India 

 desired that local Governments should make efforts 

 to ascertain the effect of such changes on average 

 rainfall. (5) The system of shifting cultivation, by 

 which large areas of forest are annually destroyed 

 In Native States and elsewhere, should be dis- 

 couraged. 



To our mind the method adopted could produce 



NO. 2492, VOL. 99] 



no better result than it appears to have done. In 

 a scientific problem such as was set forth, the only 

 function of the State seems to us to be to decide 

 that such an inquiry shall be carried out at the 

 public expense, and that every facility for obtain- 

 ing data shall be given by all the departments of 

 all the Governments concerned, local and central. 

 It should then be handed over to a competent 

 man of science set free from all other duties and 

 supplied with necessary assistants. His report 

 when complete would be authoritative and epoch- 

 making, if not final, and incidentally his own 

 reputation would be made or marred by his hand- 

 ling of the facts. The total expense would probably 

 be no greater, and the labour of many public 

 servants would not be diverted from the work for 

 which they were trained. 



Dr. Gilbert Walker's contributions on the rela- 

 tion of forests and rainfall are given as appendices, 

 but are deprived of most of their scientific value 

 by the omission of the tables and diagrams to 

 which constant reference is made. These, of 

 course, have been published in the memoirs of the 

 Indian Meteorological Department. Dr. Walker 

 fully grasps the difficulty of the inquiry. He shows 

 that in India, as elsewhere, the annual rainfall 

 has a tendency to run in spells of excessive and 

 deficient years, and that if this fact is neglected 

 totally false conclusions as to the influence of 

 forest growth or destruction could easily be arrived 

 at. He lays stress also on the short period avail- 

 able for comparisons on account of the very un- 

 trustworthy nature of the Indian rainfall statistics 

 ni the earlier years of the work of the Meteoro- 

 logical Department. 



Dr. Walker considers that, as Blanford pointed 

 out in 1887, "the only satisfactory evidence 

 would be that obtained by comparing the rainfall 

 of a district when well supplied with forests with 

 that of the same district when the trees were very 

 few." In our opinion the comparison should not 

 be that of a district A at the time t with the same 

 district at the time f' ; but to compare the relation 

 of district A to a contiguous district B at the time 

 t with the relation of A to B at time i\ where A 

 is a district that has undergone a great change as 

 regards forest covering, while B has remained un- 

 changed. The reason for this indirect comparison 

 is, of course, to eliminate the effect of the two 

 periods falling in what Prof. H. H. Turner calls 

 different climatic chapters. Another method would 

 be to determine the relation of the isohyetal lines 

 to the configuration of the land on wooded and 

 treeless districts of similar character. As pointed 

 out in the report on the rainfall in the Geological 

 Survey's "Water Supply Memoirs of Hampshire," 

 the district of the New Forest shows a consider- 

 ably higher general rainfall than its elevation 

 above sea-level appears to suggest. The subject 

 is both fascinating and important, and the time 

 will no doubt come when increase of accurate 

 observations will enable the vague belief in the 

 beneficial influence of forests on climate to be sup- 

 ported or corrected by definite meteorological 



evidence. 



Hugh Robert Mill. 



