rNTLUENCE OF FOKEST ON HUMIDITY OF SOIL. 199 



fact of a change of climate, but, on the other hand, it is equally 

 insufficient to estabhsh the contrary. Meteorological stations are 

 too few, their observations, in many cases, extend over a very 

 short period, and, for reasons I have abeady given, the great ma- 

 jority of their records are entitled to little or no confidence.* 



Influence of the Forest on the Humidity of tJie Soil. 



I have hitherto confined myself to the influence of the forest 

 on meteorological conditions, a subject, as has been seen, full of 

 difficulty and uncertainty. Its comparative effects on the tem- 



* Since these pages were written, the subject of forest meteorology has received 

 the most important contribution ever made to it, in several series of observa- 

 tions at numerous stations in Bavaria, from the year 1866 to 1871, published 

 by Ebermayer, at Aschaffenburg, in 1873, under the title : Die Physikalischen 

 Einwirkungen des Waldes auf Luft und Boden, und seine KlimatologiscJie und 

 Hygienische Bedeutung. I. Band. So far as observations of only five years' 

 duration can prove anything, the following propositions, not to speak of many 

 collateral and subsidiary conclusions, seem to be established, at least for the 

 localities where the observations were made : 



1. The yearly mean temperature of wooded soils, at all depths, is lower than 

 that of open grounds, p. 35. 



This conclusion, it may be remarked, is of doubtful applicability in regions 

 of excessive climate like the Northern United States and Canada, where the 

 snow keeps the temperature of the soil in the forest above the freezing-point, 

 for a large part and sometimes the whole of the winter, while in unwooded 

 ground the earth remains deeply frozen. 



2, The yearly mean atmospheric temperature, other things being equal, is 

 lower in the forest than in cleared grounds, p. 84. 



8. Climates become excessive in consequence of extensive clearings, p. 117. 



4. The absolute humidity of the air in the forest is about the same as in open 

 ground, while the relative humidity is greater in the former than in the latter 

 case, on account of the lower temperature of the atmosphere in the wood, 

 p. 150. 



5. The evaporation from an exposed surface of water in the forest is sixty- 

 four per cent, less than in unwooded grounds, pp. 159, 161. 



6. About twenty-six per cent, of the precipitation is intercepted and pre- 

 vented from reaching the gxoimd by the foliage and branches of forest trees, 

 p. 194. 



7. In the interior of thick woods, the evaporation from water and from earth 

 is much less than the precipitation, p. 210. 



8. The loss of the water of precipitation intercepted by the trees in the forest 

 is compensated by the smaller evaporation from the ground, p. 219. 



9. In elevated regions and during the summer half of the year, "woods tend 

 to increase the precipitation, p. 202. 



