Cape National Forests. 63 
that woods are always moist; no wonder therefore that they con- 
tribute much to pools and streams.” In South Africa, on account 
of the hotter sun and more drying winds, the protective or water-. 
conserving action of forest is greater than in England. Several 
cases have been brought to my knowledge in South Africa where 
streams have dried up or diminished after clearances and have again 
increased in strength with the restoration of the forest. At Knysna 
the roads are only kept dry enough to be passable by cutting, and 
by keeping cut, at considerable expense, the forest bordering the 
roads. To produce its full moisture-conserving effect the forest 
must be dense and composed preferably of slow-growing species. 
This then is the action of forest on moisture under ordinary 
climatic conditions. Under certain extreme conditions of drought 
trees will lower and exhaust the little remaining subsoil moisture, 
while their watery exhalations will have little appreciable effect in 
moderating the parched atmosphere, and their protective covering 
to the soil is of no use since all superficial moisture has vanished. 
In America and other countries there usually exists a belt of poor 
open forest between the dense forest of the fertile country and the 
treelessness of the quite arid country. It is probable that in the 
open forest of this itermediate zone the trees exhaust more 
moisture than they conserve, at any rate during droughts, and can 
thus only subsist in a sparsely scattered condition. Scattered trees 
and open forest in most cases exhaust more moisture than they 
conserve. Hence the erroneous conclusions not infrequently drawn 
by unskilled observers as to the true action of complete, viz., dense 
forest. Very fast-growing trees such as the casuarina in India, 
the blue-gum and other eucalypts in South Africa, use up enor- 
mous quantities of water in their vegetative process, and usually 
(especially as young trees) exhaust more moisture than they con- 
serve. This has happened with the casuarina plantations in Mysore 
and the Braamfontein plantations near Johannesburg. A common 
effect of blue-gum planting may be referred to here. The blue-gum 
is a native of a cool, damp climate. When planted in a dry, warm 
climate it is singularly active in drying up marshes, wells, springs, 
and all moisture that is within reach of its powerful vegetation 
functions. We see here in fact the struggle for existence of a young 
vegetative giant too often misplaced by man ! 
To obtain the maximum water-conserving action of forest dense 
masses of slow-growing trees (preferably of the pine class) should be 
planted. All trees, the water-exhausting trees such as eucalypts 
especially, pour vast quantities of water vapour into the atmosphere. 
When and how that vapour will condense into precious rain and 
