CHAP, x.] Stimulation of Increment 219 



already far past their normal maturity, and have begun to show 

 signs of the loss of energy in growth due to a foreshadowing 

 of the approach of senile decay, they must receive a fillip from 

 admission to larger growing-space and freer exposure to light 

 and warmth. When, however, the vital energies of the trees 

 are weakened by age or disease, normal enhancement of 

 increment need not be looked for. The circulation of the sap 

 throughout the stem must already be to a greater or less extent 

 interfered with ; whilst the root-system is also unfitted to 

 discharge the extra duties it is called upon to perform. Trees, 

 that are not very far past the period at which their current 

 annual increment has culminated, as well as such as have not 

 yet attained the culminating point, are, however, unquestion- 

 ably stimulated to livelier energy, which manifests itself in 

 enhanced increment. But, in practice, this system of partial 

 clearance, for the speedy formation of the more valuable 

 assortments of timber, is seldom applicable to very young 

 woods, or to crops that are already much older than the usual 

 periods of rotation. It generally finds proper scope only in 

 mature crops of high forest and in those approaching maturity. 

 And in these cases the age of the crop has little influence on 

 the length of time throughout which the enhancement of 

 increment is maintained ; for this is determined rather by the 

 length of time which it takes the crop to form close canopy 

 once more. The nature of the development of the crown is, 

 however, of greater importance than the age of the crop. If 

 the previous thinnings have been neglected, and if the canopy 

 has been allowed to remain so dense that the woods are 

 crowded, it often happens that, on receiving increased growing- 

 space, the trees with their weakly crowns are unable to avail 

 themselves of the advantages thereby offered, and exhibit, 

 as may so often be seen in the case of Oaks, a tendency 

 to the development of dormant buds, which leads to ' stag- 

 headedness' or death of the crown, and malformation of 

 the bole. 



