140. 



and transpiration from plant , nnd therefore affects the moisture 

 contents and condition of soil. A warmer slope dries more and there- 

 fore grows wanner. This may often reach an aggravated condition. 



jf. Topography affects transportation of soil. It is the 

 gre^ t influence. 



. Topography determines drainage and water distributiona and 

 levels, the abundance of moisture, and therefore the moisture contents. 

 Topography locates swamps, and it may fill them up bodily with soil 

 material, also lakes, and peat bogs, 



3.. Climate ( temperRture.moisture, wind) affects soil. 



ii. Arid soils are rich in salts regardless of temperature. 



To. Humid soils are constantly leached and must rebuild. In 

 deep sands rebuilding is a precarious process: there is little to build 

 from, and the soil must stay poor, often too poor for any vegetation, 



. Low temperature and low (great?) soil moisture aggravate 

 the c?se and give cold sour dead soils. 



cl. Wind affects soils in arid countries and with very poor 

 soils it transports and drifts the soil. In mountains with&i&fc S# expo- 

 sures the wind aids drying, especially in the upper soil layers and 

 therefore it affects most the reproduction of growth. Keating aggravate 

 wind circulation, 



e,. Snow affects soil temperature in winter and spring, pre- 

 v-ints frost and affects percolation and saturation of the soil, and the: 

 fore Mffectn the underground runoff. 



. otony material left by water &&a& protects the soil from 

 erosion, and evaporation, and tends to raise the soil temperature. In 

 Pennsylvania and the Appalachians it tends to warm the soils. 



0) Biotic Factors of Site. 



Here will be discussed the effects of plants and animals. 



]L. Plants and animals may help, hinder, and sometimes prevent 

 forest growth. 



a,. Plants and animals bearing some relation to the fertility 

 of the soiT have been discussed before, and so here we will discuss 

 only those? -.-hich are not connected with the soil but which affect 

 trees and their development directly, 



la. livery forest tree 100 years old has probably been attacked 

 somewhere by insecis and fuftgi for more than 75 years. 



. ivery forest tree 100 years old has shed leaves, baric, roo 

 and has beeri mutilated by the wind, and therefore portions have been 

 broken away and destroyed, 



ci. .iSvery kind of forest tree is suoject to attacks of many 

 fungi and insects, and most trees are eaten in parts by animals. 



. More than ?00 species of insects attacks the oaks in the 

 United 8t*T*s They destroyed completely the tamarack, and the pine in 



