EDITORIAL 



341 



and everywhere steps are being taken to increase the 

 productivity of the forest. Even England, which has 

 hitherto been most backward in this respect, has recently 

 adopted a comprehensive program for the planting of 

 1,700,000 acres. Is it not high time for the United 

 States to adopt a similar policy and to pass from the stage 

 of mere forest domination to that of forest restoration 



and improvement? Already we are feeling the effects 

 of forest neglect in depleted supplies and increased prices. 

 Why not follow the dictates of common sense and justify 

 our reputation for practicality by taking immediate steps 

 to stop the present indiscriminate devastation of our 

 forests and to provide for their perpetuation and in- 

 creased production? 



FORESTS AND STREAMFLOW 



rPHE beneficial influence of forests upon streamflow in 

 * hilly and mountainous regions has long been recog- 

 nized by foresters and other observers throughout the 

 world. So general indeed has recognition of this influ- 

 ence become that, in order to safeguard their water sup- 

 plies, many European countries have enacted legislation 

 for the preservation of their mountain forests, and the 

 United States has embarked on a program for the acquisi- 

 tion by the Federal Government of forest lands on the 

 watersheds of navigable streams. There have, however, 

 always been skeptics who have remained unconvinced by 

 the theoretical considerations and general observations on 

 which belief in the influence of the forest has been based. 

 A striking answer to these skeptics is furnished by the 

 recently published results of the streamflow investigation 

 that has been under way since 1900 at the Swiss Forest 

 Experiment Station. 



This investigation was undertaken in order to settle 

 beyond dispute just what, if any, influence was exerted 

 by forests upon run-off in the mountains of Switzerland. 

 Two small watersheds of 137 and 172 acres, the first 

 of which was almost wholly forested and the other slight- 

 ly less than one-third forested, were selected for the 

 purpose. With the single exception of the forest cover, 

 the two watersheds were strictly comparable in other 

 respects, such as form, topography, geology, and climate. 

 For eighteen years complete meteorological observations 

 have been made and accurate records of run-off main- 

 tained in the two basins. These have yielded the most 

 complete and convincing data yet available as to the 

 precise part played by the forest in the regulation of 

 streamflow. The conclusions established will, therefore, 

 be received with the keenest interest and respect by all 

 those interested in the problem. 



The results show that the proportion of the yearly 

 run-off to the total precipitation averaged practically the 

 same, approximately 60 per cent in the two watersheds. 

 The distribution of the run-off was, however, very differ- 

 ent. In general the discharge of the stream from the 

 well forested watershed was much more uniform than 

 that from the poorly forested one, with higher minima 

 and lower maxima. This difference is due to the greater 

 absorptive capacity of the forest soil, resulting from its 

 porosity and permeability, and not, as was formerly 

 thought, from its humus cover. The latter can, it is 

 true, retain a very large quantity of water, but it does 

 not give this up readily to the underlying soil. In fact, 

 a thick cover of raw humus and moss may, after it once 

 becomes saturated, actually promote surface run-off and 

 thus prevent the water from soaking into the soil. 



The water from melting snow and from short, heavy 

 downpours of rain was absorbed far more effectively by 

 the soil of the well forested area than by that of the 

 poorly forested one. Indeed the maximum discharge 

 from the former after such rains was seldom more than 

 one-third to one-half as much as from the latter. After 

 prolonged rains the effect of the forest cover upon 

 streamflow depended on the moisture content of the soil 

 at the beginning of the rain. If the soil was compara- 

 tively dry at that time its effect in preventing surface 

 run-off was quite noticeable, while if it was already 

 thoroughly soaked there was little difference in the dis- 

 charge of the two streams. Although the forest cover 

 was thus unable to prevent all floods, equally heavy dis- 

 charges from the well forested watershed did less dam- 

 age than those from the other because their velocity was 

 lower and they carried a smaller amount of eroded 

 material. All of the differences noted would have been 

 more pronounced had the well forested watershed not 

 had steeper slopes than the other, and had the latter been 

 completely deforested. 



The prevailing view as to the effect of forests on 

 streamflow is thus corroborated by the results of a care- 

 fully conducted and thoroughly scientific investigation. 

 It will be most interesting to compare these results with 

 those obtained from the very similar study now under 

 way at Wagon Wheel Gap, Colorado. The clearing of 

 the area took place a year ago, so that it will soon be pos- 

 sible to draw tentative conclusions. 



Meanwhile, the results of the Swiss investigation will 

 greatly strengthen the hands of those who are urging the 

 protection of our mountain forests as a means of safe- 

 guarding our water supplies. While the precise rela- 

 tions determined to exist there are strictly applicable 

 only to other areas with the same physical conditions, 

 careful analysis of the factors concerned leaves no doubt 

 that the demonstrated tendency of a forest cover in hilly 

 countries to check surface run-off and to equalize stream- 

 flow is universal. Added strength is thus given to the 

 policy of Federal acquisition of mountain forests, inaugu- 

 rated nearly ten years ago by the passage of the Weeks 

 Law. It is highly important that adequate funds should 

 be appropriated for the enlargement of the areas already 

 acquired. It is almost equally important that this policy 

 should be supplemented by public control of all "pro- 

 tection forests." Experience both here and abroad has 

 shown all too clearly that only in this way can the con- 

 servation of our water resources, one ,of our most 

 valuable natural assets, be assured. 



