118 Report 8.A.A. Advancemknt of Science. 



tion duriny eight moiitlis — April to Nuveiiiber — was 25'6 per cent, 

 when under cover and exposed to the wind, but only 108 per cent, 

 when protected from air curi'ents.* 



The effect of this decrease of evaporation is that a large quantity 

 of water st)aks into tlie soil ft»r the supply of the subterranean reservoirs 

 and springs. 



Effect oa Sjjriuyf^. — Another important function of forests is tlie 

 creation and preservation of springs. Tliese naturally affect the per- 

 manence of the flow in rivers : but they also have a direct economic 

 Aalue for irrigation. In South Africa it often happens that the only 

 available water a farmer has for irrigation or stock raising is the 

 supply drawn from small springs. As these not infrequently cease 

 running during prolonged droughts, the problem of increasing their 

 stal)ility and flow is one of considerable importance. In such cases, 

 where the physical conditions are favourable, the autlior is suggesting 

 afforestation, or l>ui^sonneinetit,'\ as a method of obtaining this end. 

 Forests do not necessarily produce springs, as they exist in many 

 places away from forest influence ; but there is no doubt that forests 

 have an enormous effect on them. Instead of the I'ainfall running off 

 the surface in a few minutes or hours, the water filters into the soil 

 to fill the underground reservoirs. Madon in his report on the Ee- 

 planting of the Island of Cyprus states that one cutting of a wood 

 is sometimes sufficient to dry up a stream, which recommences to 

 flow some years afterwards when the forest has grown again. He 

 says he knows of hundreds of cases, and mentions that at Ventoux 

 (Provence) springs ha%e reappeai-ed since the replanting began in 

 1863. He also cites an instance in the neighbourhood of Hyeres 

 where, by setting free only a portion of the superficial springs of a 

 very imperfectly ^\ ooded forest of 2000 hectares, he was able to furnish 

 during the summer of 1877 the necessary water for the supply of 

 several villages whose springs had entirely dried up. The soil was 

 of the same nature, and the topography absolutely similar ; but fitful 

 cultivation had destroyed all the forest vegetation. ^^ In the State of 

 Iowa many old residents positively assert that springs and small 

 streams now exist where none were found before the tree-planting 

 that has lately been encouiaged by federal and state laws. The 

 settlement of the State has done away with all prairie fires, and hea^■y 

 thick beds of humus and litter have formed, which are of great value 

 in retaining the moisture from rain and snow.ji According io a 

 French writer, springs have often been known to disappear, and 

 extremely dangerous torrents formed, as the I'esult of thoughtless 

 wood cutting, but that, after the reboii<e)Hmt of the mountains, the 

 torrents ha\e disappeared and been replaced by permanent springs 



* Irriqotidii in Thnraii, l»y W. Maxwell, C.S. l)e|iartin(>iit of AiiHcnlturc, 

 Hulletiii \(.. !«». 



1 'IMk' ])laiiLiii;4 ot sliiul)N or huslies. 



X Hf/thmrDiff of fit! [sldiid iif ('i//iriis, jt. S. 



§ Fnioidiatidii supplied l>y ^ir. \\. V. Baker, Koiester of low.i St;tte College. 



