than to forest trees, and that the damage in the former case would attract, in the latter would largely escape notice. Further, as regards storms and high winds in general, forests do, as has been seen, tend to check wind velocity, and thus to reduce the local violence of a gale. On the other hand, however, recent investigations in Germany have shown that in thunderstorms the obliquely descending component of the wind can be but slightly, if at all, affected by forests, whose trees are easily uprooted by these winds.
The Hygienic Influence of Forests
There are several ways in which forests have a hygienic significance, and the location of many of our well-known health resorts in or near extended forest areas is, therefore, well planned and logical. The reduced wind movement; the protection against the severest extremes of summer heat and of winter cold; the marked decrease of dust and of other atmospheric impurities; the grateful shade and lack of glare on sunny days; the relatively small number of microorganisms—all these are helpful, not only to those who are ill or convalescent, but to persons in good health; all these are arguments in favor of wooded parks in and in close proximity to our cities. In addition, but of non-climatic importance, there are the scenic attractions of the forests; the relief from the noise and the bustle of the city; the fragrance of the air among' the evergreen trees, and the frequent intermingling of river and lake and mountain, all of which features contribute to the popularity of forest sanitaria and pleasure resorts. So far as the composition of forest air is concerned, there is no further notable difference between it and the air outside. We can not, therefore, look for any marked curative effects on that account. The much-discussed beneficial effects of the ozone in the forest air seem to lack the support of observation.
The Influence of Forests upon Water-supply, Erosion and Floods
The preceding discussion has dealt with the influence of forests upon climate. Therefore no mention has been made of their relation to the conservation of the water-supply, to erosion and to floods, all of which are non-climatic, or at any rate only indirectly climatic effects. There is still a great deal to be learned about the use of forests in connection with water-supplies; their effects in holding back rainfall and in storing the winter snow; their relation to floods, and ground-water, and springs and erosion. The "last word" in this discussion is to be found in the "Final Report of the National Highways Commission" (Sen. Doc. No. 469, 62d Cong., 2 sess., 1912). From this report we take the following statements, which are of peculiar interest, because they represent the conclusions and recommendations which have been reached
