488 WEST AFRICAN FORESTS AND FORESTRY 
evaporation ; whereas the greater part of it might have been stored 
up in the forest to form perennial, almost unaltering springs, streams 
and rivers. Two interesting examples of this are seen in the slight, 
almost negligible rise in the Okwo and the Igbagon streams of the 
Benin province. Both of these rivers rise in thick forest, and thick 
forest is also found on their banks. 
In a similar way, instead of the water of the rivers being used for 
irrigating land which is sandy and dry in the dry season, it rushes 
away into the ocean for nothing. The flooding of much of the land 
near the rivers also kills many large forest trees and causes a rank 
growth of shrubs, creepers and grass, which form the breeding-places 
for tsetse and other harmful flies. It is rare to find any infected tsetse 
flies near a clear perennial stream in the forest. 
4. The forest improves the soil of a locality, whether in the 
primeval or the planted forest. The trees stand at least eighty years, and 
sometimes for several hundred, on the same land, before being cut down. 
During this period the tree roots with their root-hairs are penetrating 
far and wide into the soil, subsoil, and even underlying rock, gradually 
causing the two latter to weather into finer and better constituent 
parts. For instance, nothing appears so solid as a mountain of 
granite ; nevertheless, at the base and to the lee-side of each boulder, 
more especially if there is any tree-growth there, a beautiful little 
bed or pocket of blackish soil will be found. Then, again, besides this 
weathering of the subsoil and rock, the tree leaves, even from ever- 
green trees, fall down, gradually decay, and form a. thick layer of humus. 
This in itself forms an almost ideal seed-bed. At the edge of forests 
this humus is washed out on to the agricultural lands and thus enriches 
them ; furthermore, dry leaves are blown out of the edge of the forest 
on to neighbouring agrcultural land, become dug in, or drawn into 
the land by insects, and so tend to enrich it. In many civilized 
countries a regular business is done in taking litter and leaf-mould 
out of the forest to neighbouring garden and farm lands. 
It is a well-known fact that when a forest is cut down after some 
hundreds of years many plants appear in the clearing which did not 
exist in the forest before, or, in fact, were not known in that locality, 
the seeds having lain dormant during the whole period of time. This 
clearly shows that the forest soil is an ideal medium for preserving 
seeds, and that it improves rather than deteriorates, which is the 
case with bare land. An instance of this from the Tropics is seen 
in the way in which the Corkwood or Umbrella Tree (Musanga Smithit) 
comes up after the mahogany and evergreen forest has been cleared. 
No Musanga trees are usually found in the primeval forest. A parallel 
example from Europe is seen in the way in which Atropa belladonna 
almost invariably appears when a beech forest is cut down. 
Planting trees and thus forming a forest, though expensive, is 
