PRUNING 199 



kept growing at their fastest rate, artificial pruning often will 

 be required. In plantations the argument has especial weight. 

 Here in order to save expense trees are set out at the rate of 

 800 to 2500 per acre, with the average number around 1000 

 to 1200. As compared with the stands of several thousand 

 trees per acre frequently starting on areas naturally repro- 

 duced, this is a small number and results in a stand not very 

 densely stocked. Such plantations, if they are to yield clear 

 lumber in appreciable amount, demand artificial pruning. 



The inherent ability of the species to prune naturally is of 

 fundamental importance in determining the need of artificial 

 pruning. Light demanding species on the whole prune more 

 quickly and completely than shade endurers; but this is not 

 an infallible rule. Certain species, of which red oak (Quercus 

 r ubra) is one, prune naturally much better than other species 

 which are more light demanding. 



Forest pruning may consist in the removal of either dead 

 limbs or live limbs. It is evident that there can be no harm 

 to the tree through pruning dead limbs. The removal of 

 live limbs may be the source of injury in two ways: 



(a) Fungi and insects are afforded opportunity to enter the 

 tree through the branch scars. Where only small branches 

 are cut the wounds may heal over quickly and injury be 

 prevented. 



(b) The balance existing between the crown and the root 

 systems is disturbed and as a consequence the growth is 

 likely to be retarded. The extent to which this may occur 

 depends upon the proportion of the live crown which is 

 removed in the pruning. 



As an example of the effect of live pruning on height growth 

 the following figures relating to an experiment conducted by 

 the author in a white pine (Pinus Strobus) plantation are 



