214 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY 



production of timber ensues from adherence to this policy, for it 

 is quite conceivable that greater crops might be obtained by 

 planting in other media. The claim, however, is advanced that 

 under optimum natural conditions there is produced maximum 

 yield compatible with maximum vitality. The farmer and 

 gardener by suitable additions to the soil increase the yield, not 

 however without undermining the resistant capacity of the plants 

 concerned. To safeguard their crops control is extended and 

 various artificial means are adopted to prevent, or to remedy, an 

 outbreak of disease. The extensive area of forests, the height 

 of the trees, the inferior value of the crop do not warrant the 

 expenditure involved in such control. Circumstances for the 

 time compel us to endow, as far as lies in our power, the con- 

 stituent members of our woods with the maximum resistant 

 capacity to disease. Mycologists and entomologists well know 

 how many fungi and insects revel in the opportunity for 

 dissolution and disorganisation afforded by suppressed and 

 sickly trees in a wood. " Indisposition " in a tree occurs when 

 some factor or factors of the environment become limiting, when 

 they are present in quantities outside the range required for 

 normal health. Under such conditions the resistant capacity 

 of the tree to ever-present enemies is impaired, and the latter, 

 finding conditions favourable, gain a foothold, with the result 

 that the tree languishes and eventually succumbs. It is then at 

 all times advisable to have the tree's maximum resistant 

 capacities developed, and this is achieved by compliance with 

 nature's laws. While we cannot hope to eliminate disease, we can 

 at least establish conditions inhibiting such from becoming 

 epidemic. If by adopting this method we do not get maximum 

 yield of crop, the difference or loss is more than counterbalanced 

 by the expenditure involved in protection. 



In our consideration of a habitat we must include, besides the 

 soil and climatic factors, an analysis of the living environment of 

 plants and animals. Trees vary in their equipment for fighting 

 other species of trees and non-arboreal vegetation, and in their 

 capacity to resist animal attack. The occupancy of any habitat, 

 therefore, may be determined not by inability of any species of 

 tree to grow and flourish there, but by its inferior competitive 

 qualities which compel retreat to localities less desirable. 



The foregoing considerations in any well thought out scheme 

 of afforestation will influence the choice of species for a par- 



