IMPROVEMENT THINNING. 13 



tions separated in theory, though they may be combined in 

 practice. Another case, and a common one, is the prepara- 

 tion of a partially grown-up abandoned field for planting. 

 In such places there are often small groups of excellent 

 natural growth that can be thinned to advantage, while the 

 ground is being cleared of scattering, limby trees as a 

 preparation for planting. 



IV. RESULTS OF THE THINNING. 

 More Trees and Better Lumber. 



As improvement thinnings tend to the better spacing of 

 the trees on a given area, their tendency is to a more 

 complete utilization of the soil. If, when twenty trees are 

 struggling with each other for survival, and so fiercely that 

 all but five would be more or less injured, the forester can 

 step in and make ten healthy, vigorous trees grow, then the 

 soil over a given area will be made to produce much more 

 per unit of area than when thinnings are not practised. 



It is a self-evident truth that a stand in which the better 

 timber trees are given the advantage will produce a higher 

 percentage of good lumber than a stand in which the better 

 trees are not given the advantage. 



., Shorter Rotation. 



One of the principal advantages that are derived from im- 

 provement thinnings is that the rapidity of growth is in- 

 creased, and hence the time that it takes to grow a crop of 

 trees of a certain size is shortened. 



Improvement thinnings are of comparatively recent intro- 

 duction in this country, and it is not definitely known how 

 much the rotation of crops can be shortened ; but, judging 

 from many years' trial in the forests of Europe and from a 

 brief experience in America, it is safe to say that the rotation 

 can be materially shortened. 



This means a great saving in the long run. Suppose, for 

 illustration, that it takes fifty years to grow a crop of pine 

 boxboards on a given piece of land without the stand being 

 thinned. Now, such a crop should be produced in forty- 



