14 



ment of light, these are dominated trees ; others are so suppressed that they are 

 actually deprived of direct light, and eventually die. Even the dominant trees are 

 not all able to develop to the fullest extent, and form good timber ; and therefore 

 the forester has to thin the wood before the trees grow weak and lanky, and provide 

 a suitable growing space for them. The following table may be taken as an illustra- 

 tion of the increasing amount of space required for trees as they grow older. It 

 is the result of statistics collected in the Black Forest for mixed woods of Spruce, 

 Silver Fir, Scotch Pine, and Beech : — 



Age of wood in years. Number of trees per acre. Mean growing space per 



tree in square feet. 



20 3,960 11 



40 1,013 43 



60 449 97 



80 346 126 



100 262 166 



" A. tree growing in a free position, in complete enjoyment of vertical and lateral 

 light, will develop a full crown and root system, and lay on a maximum of vol- 

 ume. This is no doubt a great point, but it is counterbalanced by serious draw- 

 backs : — 



" In the first place a wood grown in this fashion does by no means always pro- 

 duce the greatest volume per acre, as the total production is represented by the 

 average volume per tree multiplied by the number of trees per acre. Although 

 each tree in a crowded wood, has a smaller volume than one grown isolated, yet 

 owing to the greater number of trees per acre, a crowded wood may have, and 

 generally has, a greater total volume per acre than one in which the trees grow 

 isolated. Secondly, isolated trees are liable to suffer in height-growth and in 

 straightness. In the third place, such trees are frequently covered with branches 

 low down, and in consequence they produce less valuable timber. In the case of 

 Conifers the timber is also liable to be of an inferior quality, owing to the 

 greater breadth of the concentric rings. Last, but not least, open woods can- 

 not preserve the fertility of the locality ; hence they are only admissible on fer- 

 tile localities, or special measures must be taken to preserve the fertility of the 

 soil. 



" These considerations govern the most profitable growing space in any parti- 

 cular case. It is conceivable that under certain conditions the correct policy is 

 to remove all dead, suppressed, and dominated trees, and even a portion of the 

 dominant trees, while in others the dominated and even suppressed trees may have 

 to be carefully husbanded, so as to realise the objects of management in the high- 

 est possible degree." 



The forester, in judging of the amount of thinning required, besides giving full 

 weight to the objects of management, the density of the crop, and the age of 

 the wood, has also to take into consideration the species, for light-demanding 

 trees must have more space than shade-bearers, and also the character of the lo- 

 cality. " The average growing space per tree is greater in old woods, in the case 

 of light-demanding species, on good soil, and in low elevation, than under reverse 

 conditions." 



Dead trees should be removed at every thinning, as they are a constant source 

 of danger from harbouring insects and developing fungi ; and suppressed trees 

 should also as a rule be removed. The dominated trees should be retained for a 

 time if they are necessary for the purpose of preserving a complete leaf-canopy. 

 But in time even some of the dominant trees will have to be removed, as soon as 

 they begin to interf re with each other's proper development, or if they are liable 

 in a mixed wood to suppress a tree of another species which has to be 'preserved 

 for the sake of the mixture. 



With such a tree as the Cedar, on fertile soil, it will be advisable, as soon as it 

 has attained its principal height-growth to select the most promising trees, isolate 

 these by thinning heavily, at the same time establishing an underwood of a shade- 

 bearing species. As soon as the underwood is so far advanced as to be capable 

 of protecting the soil, another thinning completely isolates the trees, leading to 

 a great extension of the crown and a consequent large increase in the diameter of 

 the tree. As the crown expands, more thinning can be made. 



