400 



PRACTICAL BOTANY 



by wind, or their being felled by the lumber- 

 man, enables the seedling to grow up rapidly 

 into a large tree. Properly to show this change 

 in rate of growth would require a series of pho- 

 tographs taken at intervals of several years, 

 with increasing amounts of light supplied to 

 the young tree ; but there is often a most 

 interesting record of changed rates of growth 

 in the wood of the trunk itself (Fig. 322). 



The behavior of trees as regards tolerance 

 of shade has to be carefully considered by the 

 forester, since he must not try to start seed- 

 lings in places where they cannot continue 

 to grow. White pines would not succeed 

 under the shade of hemlocks, but the hem- 

 locks can grow under pines and may thus 

 succeed them in a wood lot. 1 



371. Problems of forestry. Forestry has to 

 do chiefly with tree planting on unforested 

 areas, and with the maintenance of existing 

 forests in the most productive condition. Suc- 

 cessful management requires much attention 

 to the choice of desirable kinds of trees for 

 planting, adapted to the region where they are 

 to grow. Single trees or portions of the forest 

 should be selected when in suitable condition 

 to be felled. Standing timber must be pro- 

 tected from all kinds of destructive agencies, 

 such as forest fires and animal or plant para- 

 sites. Felled trees must be protected from 

 decay and from attacks of boring insects, and 

 the most economical methods must be chosen 

 for felling, transporting, and working up the 

 various kinds of timber. 



1 See Pinchot, "A Primer of Forestry," Part I, Bul- 

 letin 24, Division of Forestry, U. S. Dept. Agr. 



FIG. 322. Effect 

 of thinning out 

 on forest growth 



Part of the cross 

 section of a fir 

 tree, about half 

 natural size; the 

 early growth from 

 a to 6 was very 

 slow, as the young 

 tree was shaded 

 by spruces; from 

 6 to c the growth 

 was more rapid , as 

 part of the spruces 

 were blown down 

 by a storm in 1871; 

 from c to d the 

 growth was still 

 more rapid, as the 

 remaining spruces 

 were destroyed by 

 a storm in 1885- 

 1886. After Hop- 

 kins, Division of 

 Entomology, U. S. 

 Dept. Agr. 



