FORESTS AND CLIMATE 323 



different amounts of rainfall or of snowfall. Further, the catch of a 

 gauge is markedly influenced by the exposure. In the open field, for 

 example, where there is a free sweep of the winds across the top of the 

 gauge, more rain-drops and especially more snowflakes, are carried 

 over the gauge than in a more protected location, where the drops and 

 flakes can fall more nearly vertically. Thus, a gauge in a forest clear- 

 ing where the wind velocity is somewhat reduced by the trees, ought to 

 record more precipitation than one in the open country, although the 

 actual fall might be identical in the two cases. A difference of a few 

 feet in the elevation of a gauge will also often result in a catch varying 

 considerably in two neighboring gauges. Furthermore, forests affect 

 wind directions, and this also may influence the catch in the gauges. 

 An element of great uncertainty is thus inherent in all the earlier 

 results obtained by observation, and indeed to some extent in the later 

 ones also, but it should be distinctly emphasized that every effort is 

 now made to " correct " the results for just such errors. In the 

 majority of places where parallel stations exist, the gauges in the forest 

 have actually shown an excess over those in the surrounding open 

 country. Whether this is a real excess of rainfall, or only a difference 

 in the catch, is the disputed point. 



The Lintzel Case 



There are four cases which have been frequently cited as showing 

 an influence of forests upon rainfall. There is the famous Lintzel 

 case, first cited by Muttrich. At Lintzel, on the Luneburg Heath, in 

 Germany, the rain-gauges used to show a rainfall smaller than the 

 average at a number of the neighboring stations. In 1877 a consid- 

 erable planting of young trees was undertaken around Lintzel, until 

 several thousand acres were covered. As time went on, the rainfall 

 at the Lintzel station (in an open field surrounded by the forest) 

 showed an increase as compared with that of the surrounding stations. 1 

 There are, however, reasons against accepting these apparently conclu- 

 sive results at their face value. The probability of error, the chance 

 of discovering which is greatly diminished by the " smoothing " of the 

 generalized results; the failure to make allowance for the protective 

 effect of the increasing tree-growth; a recent change in the location of 

 the rain-gauge; the shortness of the record, and the general variability 

 and uncertainty of rainfall as a whole, are all considerations which, on 

 the best of authority, may be urged on the other side. 



The Nancy Case 



Then there is the Nancy case, from France. This is a case of four 

 stations (in two pairs), two in the forest and two in the open, within 

 a small area, the altitudes and the general condition of one pair being, 



^n 1882-86 Lintzel had about 90 per cent.; in 1887-91 it had about 102 

 per cent.; in 1892-96, about 118 per cent. 



