106 FORESTS, WOODS, AND TREES 
from adjacent arable land or pasture. Small plantations 
of this kind will scarcely produce remunerative timber, 
but their establishment can be justified as a hygienic 
measure. 
As most of the gathering grounds of water supplies lie 
in hilly or mountainous districts, and often include a good 
deal of moorland, it will be of interest to discuss at some 
length the factors that influence the growth of trees in such 
situations in the British Isles. 
The existing vegetation on an area gives the most 
important clue as regards the possibility of success or 
failure of artificial plantations. In most parts of England, 
Ireland, and Scotland three well-defined zones of vegetation 
can be readily distinguished, namely, the agrarian zone, the 
zone of hill pasture, and the moorland zone. Lowest of all 
is the agrarian zone, which comprises the farm land, includ- 
ing cultivated grazing land, as well as most parks and much 
of our woodlands. In the agrarian zone there are, however, 
great tracts that have never been brought under cultivation, 
as the heaths of southern and eastern England and the low- 
lying peat-bogs in Ireland. Nevertheless, most of this zone 
was originally covered with forest, and any part of a catch- 
ment ‘area coming within it can, as a rule, be planted, unless 
conditions of the soil, like the occurrence of deep peat, 
marsh, etc., prevent the growth of trees. In other words, 
up to a certain altitude, namely, to the line above which oats 
cease to be cultivated, plantations are usually successful and 
remunerative. 
The zone of hill pasture occurs above the farm land, and 
is mainly devoted to sheep and cattle. It is very variable 
in its composition, and includes a considerable amount of 
woodland and scrub. It extends up the slopes of the hills 
and mountains, and ends practically where the soil becomes 
peaty and the moorland begins. It is probable that the 
whole of this zone was once covered with natural woods, 
and hence its great importance in schemes of afforestation. 
It constitutes a good part of the so-called waste land, 
which, it is believed, would pay better if covered with 
