Periodical Literature. 3^7 



differences in composition which in a given locality are produced by 

 the influences of soil, species, density, age and habitus dependent 

 on biological characteristics of the species. Climate must be consid- 

 ered as not capable of being influenced ; other factors, like soil sur- 

 face, air movement, water, chemical, physical and mechanical con- 

 ditions of soil and soil cover, on the other hand, although mostly 

 capable of being influenced only in a small degree, may become the 

 cause of considerable differences in the form of stands. 



Soil. The great topographic variation which is possible even 

 on a limited area is pointed out as calling forth notable variations in 

 soil quality. Differences in humus contents may produce consider- 

 able differences of development in the younger stages, while later 

 mainly the light and the physical and chemical conditions of soil are 

 important, and especially drainage conditions. 



Species. The species influence form of stand by making differ- 

 ent demands on the soil and at the same time influencing its physi- 

 cal condition by character of shade, density, and fall of litter. Again 

 their biological characteristics are so different, that even though 

 equally adapted to the soil their development in mixed stands 

 change its form considerably. 



Little is really precisely known as to adaptation of species to 

 soils. Root systems and their variations in different soils give indi- 

 cations as to demand on depth and moisture. Just as in the crowns, 

 there are physiolological peculiarities in the habitus of the root 

 systems, like the well known taproot and tracing root habit. 



Since broad-leaf trees make, generally speaking, greater demands 

 on soil fertility and humidity than conifers, the locally varying con- 

 tents of soil in sand, gravel, stones, may in the former produce 

 greater variation of development. The surface conditions which fa- 

 vor or retard rapid surface drainage will have similar effect, and in 

 a mixed forest difference of shade will also accentuate these varia- 

 tions. 



Another factor not to be underestimated is the retention of water 

 by the crowns, which varies with species, age, density, soil quality, 

 etc., and similarly their influence on frost conditions. 



Even-aged stands may in consequence of these variations become 

 irregular in height and development. The judgment as to whether 

 such irregularity is to be attributed to site or to species and density 



