NA TURE 



[February i, 1906 



rain is caused. This condition of forest land has 

 been remarked on by aeronauts, who find that a 

 balloon is invariably affected, and drops when passing 

 over forests. 



The advantages claimed for forests with regard to 

 water supply are that the trees act as regulators of 

 the rainfall; that the average quantity of rain 

 falling on land covered with forests is greater than 

 in the open ground to the extent of about one-sixth ; 

 that it holds up the water for a time and discharges 

 it later on when water is most required in river basins, 

 the rain being held back by the leaves of the trees 

 and coming to the ground more gradually ; the rain 

 that falls on the surface is also taken up bv the layer 

 ol dead leaves on the ground, which permits of a 

 gradual percolation to the subsoil. Observations show 

 that in summer the ground of the forest is damper 

 than that of the adjacent cleared land, and snow re- 

 mains for a much longer period in forest land before 

 melting than in cleared land. 



On the other hand, it has been contended by some 

 of those who have made a study of sylviculture that 

 forests do not increase the quantitv of water flowing 

 to the springs and rivers, but" reduce it. The 

 numerous striking facts quoted do not bear out this 

 contention, which is mainly based on the fact that 

 the substratum water stands at a lower level on 

 forest land than in the adjacent cleared ground. 

 This fact is generally admitted to be the case 

 at one period of the year. As the result of many 

 years' observations, it has been found that the maxi- 

 mum level of underground water is reached in May, 

 that the water accumulates in the ground from 

 August to January; and that the rivers are supplied 

 by this reserve, and were it not for this accumu- 

 lation many brooks and river feeders would cease to 

 flow in summer. 



Several very striking examples are given by the 

 authors of the papers as to the deleterious effect of 

 cutting down forests, especiallv in hilly districts. In 

 the commune of La Bruguiere, the "forests on the 

 slopes of the Black Mountain were cut down ; the 

 consequence of this removal of the trees was that a 

 brook which ran at the foot, and the water from 

 which was used for driving some fulling mills, be- 

 came so dried up in summer as no longer to be of 

 any use, while in winter the sudden floods caused 

 very great damage in the valley. The forests were 

 re-planted, and as the trees grew up the water coming 

 to the brook was so regulated as to serve its former 

 useful purpose in driving the mills, and the torrents 

 in winter were moderated. Several other examples 

 <>l a similar character are given. 



In Switzerland, amongst other examples is quoted 

 one that occurred in the canton of Berne, where, 

 owing to the re-planting of the mountain-side witli 

 fir trees, the water again appeared at a spring which 

 had ceased to flow. After a period the trees were cut 

 down and the land converted into pasturage, since 

 when the spring has almost disappeared, only open- 

 ing nut at occasional intervals. 



In the Kazan district of Russia, once celebrated for 

 us forests of oaks and linden, which are now nearly 

 all cut down, there were formerly seventy water-mills 

 constantly at work. Less than half now can be 

 worked, and even they only run half time, and are 

 idle in summer for want of water; while in winter 

 the little rivers that worked these mills are converted 

 into impetuous torrents, breaking up the mill dams 

 and doing other damage. These abandoned water- 

 mills stand out as a striking proof of tin con- 

 sequences of tine destruction of forests. 



In Sardinia, where the surface consists of plutonic 

 rocks covered with a thin layer of earth, all the 

 NO. 1892, VOL. 73I 



streams have a rapid slope. The woods, which 

 occupied in 1870 an area of more than j\ million 

 acres, or about 43 per cent, of the whole surface of 

 the island, now are reduced to about one-sixteenth of 

 this area. Since the removal of the trees the floods 

 in the rivers rise with a rapidity and flow with a 

 velocity never known before, and a great number of 

 bridges have been destroyed by the floods. The beds 

 of the channels have been raised in some places above 

 the surface of the land, owing to the detritus brought 

 down in floods. 



In Wisconsin, U.S.A., the settlers cut down the 

 forests and converted the land into tillage and pasture. 

 During a period of about seventy years nearly the 

 whole of the forest land was thus cleared, with the 

 result that, as the forest disappeared, the water in 

 the river became lower; finally thirtv miles of 

 the channel entirely dried up, and many water-mills 

 that were formerly worked bv the stream are now 

 deserted and useless, owing to the want of water 

 to run them. 



In Sicily, owing to the cutting down of the forests 

 on a vast scale in the province of Messina, the bed 

 of the river has been raised by the stones and earth 

 carried down by the torrents so as to stop all drainage 

 from the land, and great damage has been done bv 

 the floods. Several other examples are given to the 

 same effect where forests have been cleared in the 

 same district, and these are compared with other 

 streams where the forests still exist and their con- 

 dition remains unaltered. In the former case, land- 

 slides from the mountains have become very frequent. 



VARIATION OF GLACIERS. 1 



THIS interesting report of the Commission Inter- 

 nationale des Glaciers shows that these ice- 

 streams still continue to diminish in those parts of 

 the world which it has been possible to examine. 

 In the Swiss Alps, of ninety glaciers observed, not 

 one shows an advance, which fully confirms the 

 general results of the last seven years, and indicates 

 that any slight variation is now at an end; the same is 

 true of the Italian Alps, though some of them give 

 sie-ns of increase in their upper parts. In the French 

 Alps (Pelvoux district), the Glacier Noir has steadily 

 decreased since i860; the Glacier Blanc, after de- 

 creasing from 1865 to 1886, advanced from about 

 1S89 to 1896, but is now again retiring. It is note- 

 worthy that the average elevation of the supply basin 

 of the former is from 2500 to 2800 metres, and of 

 the latter from 3000 to 3300 metres. In the Savoy 

 Alps the shrinkage continues, some small glaciers 

 having disappeared. The same is true in the 

 Pyrenees. 



In Norway both snowfall and temperature were 

 rather variable in 1904, but the glaciers, with a few 

 exceptions, have retreated; and in Greenland the 

 Jakobshavn Glacier has shrunk, sometimes rather 

 considerably. In the Caucasus (central) the glaciers 

 continue to retreat; less is known of the eastern 

 district, but the same apparently is true of it. During 

 the past year M. Fedtchenko visited more than no 

 glaciers in the Pamir, and has stated that all appeared 

 to be diminishing. The same is true, with a few excep- 

 tions, of the north-western part of the L'nited States, 

 as well as of the mountain region of western Canada. 

 In Africa, though the rainfall had been unusually 

 heavy in the Kilimanjaro district, the amount of 

 snow in the crater of Kibo had not, according to 



1 " Les Variations pcriodiques des Glaciers." Dixteme Rapport, 1904- 

 Rddige par H. F. Reid et E. Muret (Extrait des Archives des Sciences 

 phystgues et naturelles, t. xx., juillet et aoiit.) Pp. 34. (Geneve: Georg 

 et Cie, 1905 ) 



