pool : the vegetation of the sandhills of nebraska 263 



The Woodland Formations 



There is an extremely small amount of woodland vegetation to 

 be found in the sandhills. The arborescent plant life found here 

 represents associations of woodland species that have migrated via 

 stream courses from the woody formations to the east or west. 

 Furthermore the species represented in these associations are greatly 

 reduced in number and the individual plants are as a rule conspicu- 

 ously smaller than those found in similar combinations nearer the 

 centers of development of the eastern and western contingent. 

 Although the woodlands of the sandhills are meagre it is a note- 

 worthy fact that the invasion of numerous secondary woodland 

 species has been made possible only along the above lines of migra- 

 tion, and that to-day we find many such species that have penetrated 

 far into the region. 



There are two kinds of forest or woodland formations to be 

 seen along the streams of the sandhill region. One of these is 

 essentially a hroadleaf combination represented by narrow belts or 

 tongues of tree growth that have pushed westward via stream 

 courses from the wooded bluff region contiguous to the Missouri 

 River. It is therefore seen that this type is related to the great 

 climax mesophytic broadleaf forests of the Mississippi-Ohio valley 

 forest complex. The other, less frequent and typical, is of a 

 coniferous nature representing the easternmost extension of the 

 coniferous forest complex of the Black Hills and Rocky Mountains. 

 Both types of woodland follow stream courses into or across the 

 hills, never wandering far from the immediate valley or canyon with 

 its narrow flats or bluffs and ridges. The topographic features of 

 the stream courses of the sandhills have already been indicated. 



The Broadleaf Forest Formation 



One of the most prominent geographic facts in regard to the 

 sandhills is that many spring-fed streams of constant volume rise 

 in the northern portions of the region, follow a northerly course, 

 and finally enter the Niobrara, while few such streams come to the 

 same drainage course from the harder land north of this main river 

 of northern Nebraska. The reason for this difference is probably 

 found in the relative absence of large areas of water-soaked sand- 

 hills to the northward. The soil there is mostly firm and clayey of 

 the nature of short-grass land so that run-off is great and soak-in 



