VEGETATIVE SUCCESSION UNDER IRRIGATION 



By J. Francis Macbride 1 

 Agricultural Experiment Station of the University of Wyoming 



INTRODUCTION 



The data given in the following pages are compiled from observations 

 made during the growing seasons of 1912, 1913, and 1914, on a ranch 

 situated near Rock River, Albany County, Wyo., in the southeastern part 

 of the State. The Union Pacific Railroad makes the altitude at the 

 station 2,105 meters. As the part of the ranch with which we are con- 

 cerned lies about 3 miles up Rock Creek, the altitude will approximate 

 2 , 1 34 meters, a figure that corresponds very well with the general elevation 

 of the Laramie Plains (including the Laramie Basin), of which this is a 

 section. 



Several years ago the hay yield of the ranch, obtained entirely from 

 the natural meadow lands, fell short of the consumption. Means were 

 taken to increase the hay acreage by the transformation of bench land 

 to meadow, a transformation accomplished simply by flooding during 

 the successive growing seasons. This method has proved so success- 

 ful that each succeeding year has seen greater and greater areas flooded 

 until now large reservoirs (PL CI, fig. 2) are required to augment the 

 water supply during the midsummer season. 



Of course it takes several seasons to complete this change, and the 

 following notes are the result of a study of the various phases of vege- 

 tation through which the bench land passes in this transition to meadow. 

 At the time these observations were made (1913 and 1914) several ad- 

 joining tracts, each flooded for the first time in a different season, fur- 

 nished an unusual opportunity for the comparison and study of their devel- 

 opment from year to year and at the same time gave striking physical 

 evidence of actual differences in the vegetation present. I refer to the 

 varying tones of green which the different tracts assumed as the season 

 advanced — a condition so marked that with a very little practice one 

 could ride over the ranch and state authoritatively that this section has 

 been under water for four years, this for two, and so on. Indeed, it 

 was this beautiful blotching of the landscape with various shades of 

 green and brown that led to the discover)^ of what was really happening. 



1 This work was done under the direction of Dr. Aven Nelson, of the Wyoming Experiment Station. 

 If the conclusions, based on a study that was conceived in a spirit of helpfulness, prove of value, the credit 

 can not be too largely assigned to the active interest and kindly encouragement of my adviser. The dis- 

 tressing difficulties under which the photographs -were secured could not have been overcome except 

 by Dr. Nelson's perseverance and constant help. I wish to thank Prof. A. S. Hitchcock, of the United 

 States Department of Agriculture, for determining my material of the genus Agropyron; also Mr. V. H. 

 Rowland, who furnished the determinations of the difficult genus Carex. 



A collection of plants illustrating the salient features of the Rock Creek upland and meadow floras and 

 substantiating the points brought out in this study is deposited in the Rocky Mountain Herbarium at 

 Laramie, Wyo. 



Journal of Agricultural Research, Vol. VI, No. 19 



Dept. of Agriculture, Washington, D. C. Aug. 7, 1916 



ew Wyo. — 1 



(741) 



