TREES AND SHRUBS FOR THE NORTHERN PLAINS 43 



.; *, 



Figure 12. — A high percentage of Ulmus hybrids with U. pumila as one parent 

 have an excellent growth form. It is believed that the hybrids hold consider- 

 able promise for windbreak and ornamental purposes in the area. 



rainfall may not exceed 6 or 7 inches. Also, the evaporation rate 

 during the growing season is generally very high. 



Not all of the species listed in table 4 can be recommended for 

 planting in the area. Some died shortly after passing the 10-year 

 mark; others survived for much longer periods but exhibited unfavor- 

 able characteristics. A few species were tested for only a short time. 



Most of the data are based on trees grown under dry-land conditions. 

 However, observations were made of a number of species (not in test 

 plots but corresponding to test species) that were under irrigation 

 or were growing under favorable moisture conditions. These ob- 

 servations as well as the test data have been drawn upon in making 

 up the recommended list of trees and shrubs and their suggested uses 

 that are presented in table 5. 



Many species that killed back repeatedly or failed under dry-land 

 conditions were found to be hardy and of long life when given supple- 

 mental water. Examples of such species are those of Populus and 

 Salix, which under dry-land conditions killed out at comparatively 

 early ages and suffered heavy winter injury during the period they 

 were alive. Identical species planted a short distance away at ap- 

 proximately the same time, and under irrigation, did very well in 

 their 35 to 40 years of growth. 



The application of irrigation water at the proper seasons of the 

 year was highly beneficial to most trees and shrubs; its use is highly 

 recommended. Irrigation early in the fall may sometimes prove 

 harmful to species of indeterminate growth habits in that it tends to 



