BOOKS AND CURRENT LITERATURE 



The Ecology of Prairie and Woodland. — After a hiatus of 

 eighteen years the activity of the Botanical Survey of Nebraska has 

 been resumed under the direction of Raymond J. Pool, and the 

 first of a new series of papers on the vegetation of the state has ap- 

 peared. This is a study by J. E. Weaver and Albert F. Thiel of the 

 conditions existing in the tension zone between prairie and woodland, 

 and is based on work in both Minnesota and Nebraska. ^ Throughout 

 the summer months weekly or fortnightly readings were taken of the 

 moisture of the soil at to 10 cm. and 10 to 30 cm., and measurements 

 of the evaporation. These data were secured in parallel series for 

 high prairie, low prairie, hazel thicket and oak forest, a series of com- 

 munities progressing from xerophytic to mesophytic in the order named. 

 The graphs displayed show that for several weeks the soil moisture in 

 the high prairie falls below the amount required by plants, as indicated 

 by the somewhat hypothetical wilting coefficient. In the hazel scrub 

 the moisture falls for a briefer period to an amount somewhat below 

 the requirements of plants. In the low prairie and oak forest the 

 moisture remains well above the minimum requirement of plants. 

 The evaporation graphs show that the readings for this condition are 

 progressively lower as we pass from the more xerophytic to the more 

 mesophytic communities. Measurements were made of the rates of 

 transpiration of the prairie rose in the prairie and scrub conditions, 

 and of oak seedlings in prairie, scrub, and forest conditions. These 

 show that lower rates prevail in the more mesophytic conditions, the 

 seedlings transpiring more than twice as much in the hazel scrub as in 

 the forest, and over eight times as much in the prairie as in the forest. 



The evidence presented by the authors leads them to the conclusion 

 that the conditions of the high prairie are such as to make invasion by 

 plants of the scrub dependent on a concurrence of favorable summers. 

 The success that attends the planting of trees on the prairies has led 

 the authors to an investigation of the fate of tree seedlings, which is 

 still in progress. 



1 Weaver, J. E., and Thiel, Albert F. Ecological studies in the tension zone 

 between prairie and woodUxnd. Bot. Surv. Neb. New Series No. 1, pp. 60, figs. 

 38. Lincohi, 1917. 



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