356 Forestry Quarterly. 



naturally be drawn between the influence which strips of trees, 

 such as windbreaks, and that of large bodies have upon the sur- 

 rounding land. Here also should be described the conditions 

 which exist for natural reproduction in natural parks, meadows, 

 or other openings in the forest. The forest spreads and conquers 

 new territories, first, by pushing its edge further into the open 

 ground, and, second, by the assistance of some species which are 

 endowed with peculiar silvical characteristics and thus justly 

 make them forest pioneers (aspen). From such a discussion the 

 transition is entirely natural to another phenomenon, the so- 

 called rotation of species and later to forest types. 



As a part of the silvical characteristics of stands may also be 

 considered the composition and the form of stands, pure and 

 mixed, even and uneven-aged, one-or many-storied stands. 



The discussion, then, of the silvical characteristics of stands 

 should cover more or less the following points : 



Change in the physical environment of forest trees with the formation 

 of a stand ; the effects of the formation of stands upon the amount of 

 precipitation which reaches the forest floor ; effect of stand upon wind 

 velocity ; stands as means of conserving moisture in the upper strata of 

 the soil ; temperature, humidity of the air, and light conditions under forest 

 cover; evaporation under forest cover; forest leaf litter, its importance and 

 -effects; living ground cover; struggle for existence among forest trees; 

 laws of growth of stand; division of conditions of growth into site or 

 quality classes; effect of some species in forcing the growth of others; 

 silvical characteristics of one or many storied forests ; silvical character- 

 istics of pure and mixed stands; stands of seedling origin; stands of sprout 

 •origin; even-aged stands; uneven-aged stands; importance of shrubs in 

 silviculture; natural reproduction of stands; silvical characteristics of 

 natural parks, meadows, and other openings in the forest; formation of 

 iorest types. 



In this discussion there will necessarily be used many illustra- 

 tions of specific stands. It will be shown also how the character- 

 istics of stands vary under different conditions of climate, soil, 

 etc. 



The study of forest types requires special consideration. The 

 basis or criterion for determining forest types must be the physio- 

 graphic conditions of growth. Another criterion for differentiat- 

 ing a stand into forest types is the method of regeneration which 

 is dictated by given physiographic conditions of growth. The 

 division of forest types into permanent or temporary must be 

 fully explained as well as the importance of forest types for the 

 preparation of yield tables, choice of method of reproduction. 



