106 FOEESTS, 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 wliere 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 



