REVIEWS 67 



vary in general directly with the order of the communities in succes- 

 sion, the communities nearest the climax heing the most nicsophytic 

 in hoth respects. 



"The prairie and woodlands in the vicinity of Lincoln are consid- 

 erably more xerophytic than those in the neighborhood of T*eru. This 

 fact is strikingly revealed in a comparison of the ecological factor data 

 from the two areas, and it is also strongly reflected in the composition 

 of the plant communities in the two places, although the two areas are 

 only about (iO miles ai)art. Available soil moisture was (^^xhausted in 

 the i)rairie station at various dej)ths in the vicinity of Liricoln on 

 eighteen different dates in 1J)1T, from May to September, while the 

 same condition was recorded for only four dates, late in July and 

 August, in the prairie station at Peru. 



"Ecological conditions are shown to change rapidly as the forest- 

 prairie ecotone is traversed in Nebraska. Habitats rapidly become 

 more xerophilous and many of the more mesophytic species drop out 

 entirely between Peru and Lincoln. It is thus shown that the natural 

 extension of our native woodlands is greatly hindered, possibly alto- 

 gether prevented in so far as any significant permanent extension is 

 concerned, by the increasing severity of natural environmental condi- 

 tions as we move westward away from the woodland type? of i-.outri- 

 eastern Nebraska. 



"The high saturation deficit and the low soil moisture content (often 

 reaching the non-available point) of the prairie sites in eastern 

 Xebraska constitute barriers over which forest trees can scarcely pass. 

 We probably have herein the most ready explanation as to why our 

 natural Nebraska woodlands are confined to the moist slopes of rather 

 narrow valleys, and also the most probable answer to the oft-repeated 

 question as to the treelessness of the prairies in general. 



"The common forest types or communities of the region about Peru 

 in order of their place in succession are as follows, beginning with 

 the most meso])hytic : The linden-ironwood type, the red oak type. 

 the black oak-hickory type, the bur oak-yellow oak type. A bur oak- 

 vellow oak-black oak combination is also quite common. The common 

 forest type near Lincoln is the bur oak-hickory type, often mixed with 

 elm and black walnut." 



These investigations add in no small way to the heretofore meagre 

 knowledg-e as to the cause of the treelessness of the prairies and the 

 shar]) definition of the tension zone between the prairies and the 

 adjoining woodlands. The studies also stand out in bold relief against 

 a great many purely ecological researches in that they contain funda- 

 mental conclusions welcomed by forest investigators because they are 

 directly applicable to forest problems. Anyone interested in the silvics 

 of the central hardwood species and in the treelessness of the prairies 

 would profit materially by a perusal of the original data presented in 

 these monographs. C. F. Korsti.\n. 



