IMPROVEMENT THINNING. 



seeded naturally with pine trees at approximately the same 

 distance, there will be 1,200 trees on the acre at the time 

 of starting. Each tree will have 36 square feet of space in 

 which to spread its branches. Trees, being like some men, 

 take all that their neighbors will allow ; so each of these 

 trees, provided that no accident happens to it, will grow 

 and spread out its branches until they touch those of the 

 surrounding trees. Then we have what is known in forestry 

 as a "closed stand," that is, a stand that completely 

 shades the ground. As soon as the stand is closed the trees 

 begin to crowd one another. The fight for existence is now 

 on, and those trees which, by some little accidental advan- 

 tage, manage to get ahead, are the ones that will survive. 

 By the time the stand is fifty years old there will be approx- 

 imately 400 trees standing on the acre where there were 

 1,200 at the start. The rest have perished in the fight, and 

 some of those that are still living are destined to succumb 

 within a few years. 



By interfering in this struggle at the proper time and in 

 the proper way, it is possible to avert the injury which may 

 come from too fierce a conflict, and at the same time to play 

 the trees off against one another, so that the struggle be- 

 comes a stimulating source of benefit to the individual trees 

 and to the stand as a whole. The proper way to interfere 

 is to execute moderate improvement thinnings from time to 

 time, while the trees are growing. 



The extent to which a stand of trees will respond to such 

 treatment is remarkable. The writer wishes that those to 

 whom these words are addressed could see the celebrated 

 city forest (Sihlwald) of Zurich, Switzerland. Some of the 

 stands in that forest have been thinned about once in seven 

 years since the early stages of their development. Their 

 long, straight, symmetrical trunks embody the energy that 

 might have been wasted in useless competition with their 

 neighbors. Their growth has been rapid. There are no 

 undesirable species in the stand. The ground is fully 

 utilized. 



