FOREST IN RELATION TO AGRICULTURE 489 
another way of clearly proving the beneficial effect of the forest, or 
ameliorating the condition and plant-food content of the soil. On the 
comparatively worn-out and poor soil near Ibadan a firewood planta- 
tion was started some years ago; now already, in the shade of 
the Ayin, Anogeissus letocarpus and Cassia Siamea trees, the fallen 
leaves have decayed and formed a layer of humus, killing out the 
lalang grass at the same time. Needless to say, it is a very expensive 
method to wait until the forest has been destroyed, the soil impover- 
ished, and trees again planted, before an improvement in the soil 
conditions can be expected. 
5. Individual trees, and thus trees in the aggregate, viz. forests, 
take less mineral matter out of the soil than agricultural crops covering 
a similar area. It has been calculated that the trees on an acre of 
land only take one-twelfth of the amount of mineral matter out of 
the ground which is required by an agricultural crop on the same area. 
It follows from this that trees, and in the same way forests, may be 
left standing upon or be grown on land which is nearly or absolutely 
worthless from an agricultural point of view. In the more civilized 
countries this is seen, for instance, in the way in which the mountain 
ranges of Germany have remained covered with forest and the sandy 
Landes district of France has been planted with forests of pine. 
In Canada, the Spruce Hills Reserve, near the Canadian Pacific Railway 
in Manitoba, is another example of the setting aside of poor, almost 
worthless agricultural land as a permanent forest area. In Nigeria, 
the Oban Forest Reserve and the forest-covered hills of Olokemeji 
are further examples of the practice of this principle. 
Generally speaking, in fact, in most civilized countries there are 
really three types of land, viz. : 
(a) Absolute farm-land, which comprises the very richest and best 
land of the country, in which forests should only be allowed to 
stand, as an exception. 
(6) Relative forest-land, comprising land which can be used 
permanently for agriculture, but requiring a great deal to be spent 
on improvements or manures to make it suitable for the purposes, 
but which in its natural state carries a heavy stand of timber, could 
be used for forests indefinitely. 
(c) Absolute forest-land, comprising land which, owing either to 
its elevation, aspect, soil or position, cannot be used for the permanent 
cultivation, or in some cases even the temporary cultivation, of 
crops. 
6. The forest protects agricultural land against storms and insect 
pests. In many places, owing to very strong winds, certain crops 
cannot be grown. For instance, it is said bananas cannot be grown 
at Zaria owing to the prevalent strong winds. In the Chang district 
of the Cameroons the natives only plant plantains near their houses 
