40 FORESTRY 



type constant especially when several species grow in mix- 

 ture. In some parts, one species will predominate, while 

 a different one will be in the majority in an adjoining area. 

 Out of a constantly changing forest, types are chosen by 

 deciding upon the general features of sufficient importance 

 to justify a division of the whole forest to conform with 

 the differences noted. Minor differences are neglected. 

 The basis for such divisions, or types, are usually broad 

 topographic features such as bottom land, swamp land, 

 south slopes, ridge tops, and the types so determined are 

 named from the topography. Where the type depends 

 less on topography, and more on accidental distribution 

 of species, it is named from the prevailing species or mix- 

 ture, as white pine type, Jack pine type, poplar type. Dif- 

 ferences in age do not form a basis for making different 

 types. A spruce slope type is the same type whether the 

 trees are seedlings or veterans. But if the old stand is 

 destroyed and is followed by a different species, the type 

 is changed. Thus types are recognized solely on the basis 

 of the dominant trees, which make up the bulk of the stand 

 and will produce the crop of wood. 



Forest Enemies. — The worst danger to a forest is from 

 fire. There is no region in this country free from fires, 

 and so profound is the influence of fire on the forest, that 

 the forester is forced to consider this danger before every- 

 thing else. The leaves and needles shed by trees form an 

 inflammable litter, which in dry times burns readily. Some 

 forests grow on such wet land that they seldom burn over. 

 If a swamp becomes so dry that fire runs through it every 

 tree is killed. Forests on rich soils throw a heavy shade, 

 and this with the resultant damp condition of the litter 

 prevents fire except in bad droughts. But on the drier 

 soils less shade is cast, and there is a long season each 

 year when the slightest spark will start a blaze. Sandy 

 pine lands in the South are burned over every year, and if 



