PRUNING. 285 



It is essential, therefore, that the wound should be closed as 

 quickly as possible and made impermeable to the spores of 

 fungi and to water. This is effected liy nature through the 

 process of occlusion, provided the wound does not exceed a 

 certain size. The time required for this operation depends on 

 the size of the wound, the vigour of the tree, the manner in 

 which the wound is made, and above all the species. 



Pruning green branches is least dangerous and objectionable 

 in the case of oak and most conifers which are in vigorous 

 health, provided the operation is carefully done and the wound 

 does not exceed 3 inches in diameter. Oak closes the wound 

 rapidly by occlusion, while wounds on conifers exude turpen- 

 tine, which protects them to a considerable extent. 



As regards other European species the evidence is at present 

 conflicting. Pruning green branches of poplars, birch and 

 willows is undesirable, because their wood is liable to rot 

 quickly. According to Hess some of the important species 

 may be arranged in the following descending series in respect 

 of the activity of occlusion : — Broad leaved speeiea : Oak, 

 beech, hornbeam, lime, ash, maple, birch. Conifers : larch, 

 silver lir, Scotch pine, spruce. In the case of the last- 

 mentioned species the pruning away of green branches is, 

 in the opinion of most foresters, altogether undesirable. 



Under any circumstances, the pruning of green branches 

 should not be undertaken without due consideration of the 

 advantages which are likely to be realised and the dis- 

 advantages connected with the operation; this is of special 

 importance in all cases where the objects of management 

 centre in the production of large sized timber, which can only 

 be obtained by permitting the trees to grow and increase for 

 many years after the pruning has been carried out. 



3. Execution of Pruning. 



Where the object is to produce valuable timber trees, the 

 branches should in all cases be cut off close to the main stem, 

 but without injuring the bark of the latter ; only in this way 



