192 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
4. TO WHAT EXTENT DOES ForREST AUGMENT THE 
RAINFALL OF A REGION? 
It is impossible to answer this question precisely, but at 
places where observations have been made, an augmentation of 
8 to 15 per cent. in the annual rainfall has been found. The 
matter is one which has received considerable attention from 
those who are interested in reforestation; some of them 
declaring that forests have “‘znjfinitely little” influence on the 
rainfall of a district—others asserting with truth that forest is 
of great importance. It promotes the fall of rain by increasing 
the weight of clouds with the watery vapour which it supplies; 
by chilling the atmosphere, and thus inducing condensation ; 
and by squeezing passing clouds, and thus causing precipita- 
tion. 
5. FoRESTS FEED SPRINGS. 
In hilly and mountainous country, where springs exist and the 
subterranean waters are in motion, forest plays a very different 
part. It augments and prolongs the supply of springs that have 
a deep source, and dries up superficial springs. For this there 
are two reasons :— 
1. In forests furnished with a proper layer of humus, all 
surface flow of water ts stopped by the leaves and roots on the 
ground, even though the slope may be considerable. ‘Thus, at 
the time of the melting of the winter snows, for instance, the 
water on a wooded mountain disappears in a different way from 
that on a bare or grassy one. On the bare mountain, on the 
occurrence of thaw, the snow, exposed freely to sun or to warm 
wind, melts quickly and runs down at once, having no time to 
sink into the ground. This is often the cause of great floods. 
On a wooded mountain the snow melts much more slowly, and 
even if there is not much obstruction in the way of dead leaves, 
the slowness of the thaw gives the water time to sink into the 
ground. And this ground, which is always enriched by decom- 
posed leaves and mould, acts like a sponge. It can absorb 
water up to four or five times its own weight; the soil 
immediately beneath it is also very absorbent, and the roots, 
while obstructing flow, do not drink up much moisture in winter. 
The water thus sinks s/ozw/y into the ground, and finds its way 
to impermeable strata of rock, from which springs rise. 
