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SCIENCE-GOSSIP. 



FORESTS AND CLIMATE. 

 By Herbert C. Fyfe. 



T T is only within the last twenty years or so that 

 the question of the climatic influence of forests 

 has been discussed from a scientific standpoint. 

 As is the case in so many other branches of science, 

 the best work has been done in Germany ; Weber, 

 Ebermayer, Zolluz, and Muttrich having all con- 

 tributed to the subject. In England, Mr. John 

 Nisbet, and in America, Mr. B. E. Fernow, have 

 also done good work. But though we have 

 numerous observations, extending over several 

 years, it is not safe, for the present, to draw any 

 deductions as to the influence of forests on the 

 precipitation of aqueous vapour, owing to the con- 

 flicting nature of the results of these observations. 



The Russian peasants declare that since the 

 Steppes have been planted up the summer rainfall 

 has considerably increased. On the other hand, 

 American observers say that the re-wooding of a 

 tract exerts no perceptible difference on the amount 

 of the aqueous precipitations. One observer, 

 Lendenfeld, has endeavoured to prove that the 

 clearance of woodlands in Australia has resulted 

 in a better climate and an increase of rainfall, as 

 the soil under eucalyptus remains hard as stone 

 and unabsorptive, while it is rendered lighter and 

 more porous by grass. 



Weber draws the conclusion from an examina- 

 tion of readings at 192 points of observation in 

 Germany that " At high altitudes large extents of 

 forest may considerably increase the local rainfall." 



It will be seen from the foregoing remarks that 

 there is much to bewilder the mind of the average 

 reader who is endeavouring to arrive at a clear 

 understanding of the subject. Mr. Fernow says 

 in his book on " Forest Influences," published at 

 Washington last year: "As a consequence of 

 deforestation we should expect an effect on the 

 climate of the deforested area in three directions 

 — (a) extremes of temperature of air as well as soil 

 are aggravated ; (b) the average humidity of the air 

 is lessened, and possibly (c) the distribution of pre- 

 cipitation throughout the year, if not its quantity, 

 is changed." 



Of the value of woodlands from a national- 

 economic point of view, we think there can be no 

 doubt. Lessened streams must inevitably come 

 with lessened forests. Observations made in 

 Switzerland, Prussia, and Bavaria, show that 

 nearly one-fourth of all the precipitations of aqueous 

 vapour is intercepted by the forest trees, and is 

 given off again by evaporation, or is gradually 

 conducted down the stems to the soil. 



The great value of the forest lies in the fact 

 that it acts as a barrier against the floods, 



which, but for their kindly intervention, would 

 carry away the banks of the rivers, and swamp 

 the richest pasturage. In Russia such disastrous 

 results occurred from the devastation of forests 

 that the Government issued a law for their pro- 

 tection. This, of course, is not directly connected 

 with the question, " Do forests affect rainfall ? " but 

 they are nevertheless interesting facts indirectly 

 bearing on the subject. The only true way of 

 arriving at a solution of this most important 

 question is by carefully observing the rain-gauges 

 kept at different stations. So long ago as 1769 

 Heberden showed, in a paper printed in the 

 " Transactions of the Royal Society of London," the 

 remarkable influence of altitude on rainfall. He 

 stated that a gauge on Westminster Abbey, over 

 150 feet above the ground, caught less than half as 

 much as a gauge on the ground. This diminution 

 was due to the influence of the eddies of wind 

 around the building and the mouth of the gauge. 

 Quite recently Brandis and Blandford, from ex- 

 periments with guages in the forests of the central 

 provinces of India of different altitudes, showed 

 that the high gauges in the forests gave four per 

 cent, more rain than the high ones in the open fields. 

 Another gauge at lower altitude gave two per cent. 

 greater catch in the forest than in the open land. 

 People might at first think this definitely established 

 the fact that forests do influence climate, but it 

 ought to be remembered that the high forest 

 gauges experience less wind and consequently catch 

 more rain than the high open land gauges, owing 

 to the fact that the former were at a height de- 

 cidedly less than the ninety feet by which the 

 gauges in the open lands were elevated above the 

 ground. 



Before closing these remarks a few words as to 

 the sanitary influence of forests may not be out of 

 place. Forest conditions, as far as we know, are 

 unfavourable to bacteria growth. The germs of 

 cholera and enteric fever can be carried by water. 

 These diseases, when epidemic, usually break out 

 in thickly populated towns, where it is impossible 

 to submit the soil-moisture or the water supply to 

 the filtrating action of belts of woodland. The 

 value of larger parks in cities is inestimable. They 

 establish air currents that bring fresher air to the 

 ground ; they reduce the temperature by their 

 shade ; they purify the soil by absorbing the results 

 of decomposition from animal matter ; and lastly, 

 they prevent, or at least in great manner reduce 

 the dust and bacteria in the air, and thus keep it 

 purer than it would otherwise be. 



80, Elsham Road, London, W. ; March, 1894. 



