l84 ECONOMICS OF FORESTRY. 



necessary to protect it against damage of various 

 kinds. The young seedlings of some species are 

 apt to suffer from frost or drouth, which is avoided 

 by growing them under shelter of older trees, 

 by draining wet places, securing opportunity for 

 cold air to draw off, etc., — mostly preventive 

 measures. In prairie and plain it may be possible 

 to assist their resistance to such damage by culti- 

 vating the ground as the farmer does, but in the 

 real forest country such means are excluded by the 

 character of the ground, and the expense. Alto- 

 gether the only practical remedies lie in the di- 

 rection of foreseeing the damage and guarding 

 against it. 



Animals, and especially insects, are frequently in- 

 jurious to the young crop, and insects also to old 

 trees, by their defoliation. This damage, too, can be 

 largely obviated by preventive measures. 



Since many, if not most, injurious insects are 

 monophagous, i.e. feed on one species, or at least 

 one genus, mixed forests resist their damage better, 

 since the number of host plants is reduced and the 

 intermixed trees impede progress and development 

 of the pest. Fewer insects develop in the dense 

 shade and on vigorous, healthy plants, hence they 

 can be kept in check to some extent by keeping 

 the crop dense and in vigorous development, when 

 it can resist the attacks ; and also by keeping the 

 woods clean of debris, dead and dying trees, in 

 which insects develop ; finally, as ultima ratio, 



