48 PLANT SUCCESSION AND CROP PRODUCTION 



entirely undisturbed. The best soil in southeastern Ohio is to be 

 found in the stream bottoms where the surface material washed 

 down from the slopes has accumulated. With the cutting of the 

 forests, however, many acres of fine bottom lands have been, for a 

 time at least, ruined since the erosion of the hills was rapid enough 

 to wash down sandy subsoils. Instead of leaving a fine deposit of 

 rich organic matter as is usually the case, floods frequently drop 

 a load of coarse sand and gravel and bury the best soil of the farm 

 several feet below the surface. 



From the standpoint of plant successions, the original compo- 

 sition of the soils has not had a great deal of influence upon the 

 plant life. Succession on clay soils and upon sandy soils is 

 much the same, though on the sandy soils the cycles require a 

 longer time from the initial stage to the completion of the cycle. 

 The structure of the soil, since it greatly influences the water con- 

 tent, has, on the other hand, a most important influence. In the 

 glaciated region of the state the soils were mixed thoroughly and a 

 good deal of material was clay. In the unglaciated regions the 

 soils are not mixed, except the alluvial soils, and have been derived 

 in situ largely from the underlying rock. The successions in the 

 glaciated regions have, except for the lake and swamp areas, ad- 

 vanced as far in the cycle in postglacial time as the succession in 

 the sandy and over-drained unglaciated region. In the latter area 

 the development of the vegetation has not been in any broad way 

 interfered with for ages preceding the advance of the several ice 

 sheets. 



C. The Climatic Conditions 



The influence of climate upon plant and animal is everywhere 

 considered to be of fundamental importance. In the broader geo- 

 graphic sense climate is more important than soil conditions. The 

 latter, however, frequently limit the local distribution. Elevation 

 above sea level, latitude, relation to large bodies of water and the 

 direction of prevailing winds are all factors which exert a con- 

 trolling influence upon the climate of a region. 



The effect of land relief and of elevation is to be seen in the 

 precipitation and in the length of the growing season, i. e., the 

 number of days between frosts in spring and fall. The least pre- 

 cipitation occurs in the flattest portion of the state — a part of the 

 Erie Plains (see Fig. 10), and in a narrow band southwest of Lake 

 Erie. Here the annual precipitation averages from 30 to 34 



