224 CLIMAX FORMATIONS OF NORTH AMERICA. 



years by ruderal mixtures, after which the bunch-grasses invade and later 

 the spear-grass again appears. When valley land with either spear-grass or 

 bunch-grass vegetation is broken, Hordeum jvbatum often comes in in great 

 abundance, so that such areas are very conspicuous. This same 'weedy 

 grass' also invades, along with Cycloloma, Amaranthus graecizans, and Salsola, 

 areas of the wire-grass transition association after breaking." 



Shantz^ (1916) summarizes the succession in abandoned roadways in eastern 

 Colorado as f oUows : 



"The roads are formed by driving over the sod until all vegetation is worn 

 off. After the vegetation is more or less completely destroyed the road is 

 usually abandoned for a new road on one side of this old road, and this new 

 road in turn, after a period of years, for another road formed usually on the 

 same side. In this way during a period of 20 or so years as many as 9 or 12 

 roadways have been formed. The successions show rather clearly defined 

 stages. 



" The first stage is an early weed stage found on roads abandoned from 1 to 

 3 years. The plants are principally: Polygonum aviculare, Salsola pestifer, 

 Verbena bradeosa, Grindelia squarrosa, Plantago purshii, Festuca odofiora. 



" The second stage, or late weed stage (from 2 to 5 years), is composed of a 

 dense stand of the same plants listed in the early weed stage, supplemented by 

 young plants of Schedonnardus paniculatus, Gutierrezia sarothrae, and Malvas- 

 trum coccineum. 



" The third stage {Schedonnardus paniculatus stage) from 4 to 8 years, con- 

 sisting almost entirely of Schedonnardus paniculatus and Gutierrezia sarothrae. 



" Fourth stage : A Gutierrezia stage from 7 to 14 years, consisting largely of 

 Gutierrezia with plants of Schedonnardus and occasional BuMoe. 



" Fifth stage : A Bv£;hloe dactyloides stage from 13 to 23 years. In this 

 stage, especisdly in the central part of the road which represents the earlier 

 stages, are found plants of Gutierrezia and Schedonnardus. 



" Sixth stage : The Buchloe dactyloides-Bouteloua oligostachya stage extends 

 from 22 to 50 years. It may never be reached under unfavorable conditions. 



" The reason for the succession is the destruction of the original vegetation, 

 which results in: 



" (1) Conservation of water, since water is lost through growing plants, and 

 the water content of the soil under the roadway is always higher than under 

 the native vegetation. 



" (2) The annual weeds, which are first to utilize the surface water and 

 increase gradually in number until they consume all the water available during 

 the season. 



" (3) Gradually short-lived perennial grasses, which are surface feeders, take 

 the place of the annuals. As they become established it is increasingly difficult 

 for seedlings to obtain a start during the early spring rains. 



" (4) perennials, deep feeders, wMch gradually become established are able 

 to take water from the deeper layers. 



" (5) Long-lived, surface-feeding, short grasses kill out the deep-feeding 

 perennials by utilizing all available water before it penetrates to the deeper 

 layers." 



'This summary of a forthcoming paper has kindly been furnished by Dr. H. L. Shantz, Plant 

 Physiologist, Alkali and Drought Resistant Plant Investigations, Bureau of Plant Industry. It 

 is published with the permission of the Secretary of Agriculture. 



