NOTES ON FOREST CONDITIONS IN NORTHWESTERN 



NEBRASKA. 



Raymond J. Pool. 



The position of Nebraska is unique from a phytogeo- 

 iriMphical point of view. The state lies near the geographic 

 center of the United States with its long axis of over four 

 hundred miles extending in an east and west direction. From 

 these facts it must be appreciated that there are possibilities 

 of great differences in climatic and soil conditions over the 

 two extreme ends of the state. As truly as the climate, soil 

 and general life relations of the southeastern corner of the 

 state are somewhat similar to those conditions in the Missis- 

 sippi-Ohio valley region, so these relations in the northwest 

 corner of the state, over five hundred miles away, are very 

 similar indeed to those conditions as we find them in the foot- 

 hills of the Rocky Mountains and in the Black Hills to the 

 northward. In following a line thus drawn one passes from 

 a region into which the arborescent vegetation has migrated 

 from the great southeastern hardwood forest complex, through 

 the prairie and sand-hills regions to a strikingly different 

 region characterized by arborescent vegetation that has come 

 into the state mainly from the Rocky Mountains and Black 

 Hills. In the southeast, with an average annual precipitation 

 of about 33 inches and a mean annual temperature of 53 

 degrees F. and an altitude of 850 feet, the forest vegetation 

 is composed of deciduous broadleaf species, while in the north- 

 west with an annual precipitation of about 17 inches, a mean 

 annual temperature of 44 degrees F. and an altitude ranging 

 about 4,000 feet, the forest is composed of evergreen coniferous 

 species. These two primary areas of forest invasion are in the 

 main, forever effectively separated by the great barrier inter- 

 posed in the form of prairie and arid sand-hill land. The one 

 notable case of the meeting of tree species from these two 

 opposite centers is seen along the Niobrara River in the 

 north-central portion of the state where Juglans nigra meets 

 with Pinus ponderosa. 



