1 68 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



for investigation. Its solution will probably lie in a type of 

 systematic and regular thinnings, so that the year rings, although 

 wide, will be regular in size and the increment concentrated on 

 the straightest and best formed trees 



The third point is the relation between thinning methods 

 and the health of the crop. The regular removal not only of 

 diseased (where possible) and backward or weak trees will 

 decrease both actual and potential centres of infection. Further, 

 if a thinning method succeeds in increasing the food, water and 

 liorht supply of the trees that remain, this will be reflected in 

 increased vigour and probably less liability to certain diseases. 



The last angle from which it is desired to view the problem is 

 the influence of thinnings on the forest floor. It is usually 

 recognised that the excessive weed growth which results from 

 too open a canopy is bad, but it is not always realised that the 

 opposite extreme is harmful also. Under too close canopy 

 conditions, especially under certain climatic conditions, the leaf 

 fall does not disintegrate and raw humus accumulates. What 

 should be an important source of food-supply is lost, indeed 

 becomes harmful owing to its effect on the soil. Investigations 

 on the Continent, such as Oppermann's in Denmark, have shown 

 that for certain species and conditions, heavy thinnings are 

 necessary to ensure the continuous oxidation of the humus. 

 It is essential, however, that they be carried out at regular 

 intervals and directed to secure this object. Consideration of 

 this aspect of the thinning problem is required for our country, 

 both from the point of view of the growth of existing woods 

 and the future problem of natural regeneration, which is 

 influenced notably by the condition of the humus at the end 

 of the rotation. 



Having now endeavoured to indicate the thinning problems 

 awaiting study, a short account will be given of how the 

 investigation is being carried out by the Forestry Commission. 

 As yet the Forestry Commission has few woods old enough 

 for the above purpose, hence the investigation is being carried 

 out largely in privately-owned woods with the co-operation 

 of their owners. To date, the work has been limited to pure 

 or almost pure even-aged coniferous stands. As a rule only 

 young woods about 15 years and upwards requiring a first 

 thinning are selected, so that the whole history of the thinnings 

 mav be known. A uniform and fully stocked piece of such 



