42 CIRCULAR 912, U. S. DEPARTMENT OF AGRICULTURE 



recorded during the severe drought years. The species has a good 

 form of growth and the data indicate that it is highly satisfactory for 

 windbreak planting. 



Ulmus parvifolia. — Testing of this species was confined to the 

 Mandan station. The trees suffered severe winter injury almost 

 every year. During the period this species was under test, it showed 

 no promise for planting in the area. 



Ulmus pumila.— This species has been extensively planted on the 

 northern Great Plains for both windbreak and ornamental purposes. 

 Its behavior has been somewhat erratic in that very heavy killing 

 back and losses occur in some years for no apparent reason. Severe 

 freezing temperatures early in the fall, such as occurred in 1942, 

 resulted in heavy killing back and loss. Heavy losses that occurred 

 in some years cannot be traced to any climatic factor. The species 

 seldom sets terminal buds before late in the fall. The late retention 

 of leaves and brittleness of the wood makes exposed trees subject 

 to wind and sleet breakage. Young trees are quite susceptible to 

 damage by rabbits. Despite the unfavorable factors, the species is 

 recommended for windbreak planting on all except wet sites. Trees 

 should not be irrigated in late August or in September and they 

 should always be planted among other species. U. pumila was 

 introduced from China in 1908 as Chinese elm. It is now generally 

 known as Siberian elm. 



Ulmus hybrids. — These trees are natural hybrids. U. pumila is 

 one parent and U. julva is possibly the other. The hybrids were 

 selected from a nursery field of the Soil Conservation Service at 

 Vermillion, S. Dak. In the test block, four of the trees lacked vigor 

 and suffered repeated winter injury before dying between the fifth 

 and eleventh years. The other trees suffered no injury and maintained 

 a vigorous condition. A high percentage of these trees have an 

 excellent growth form (fig. 12) that is free of the heavy branching and 

 sharp crotches so characteristic of U. pumila. Most of the trees 

 drop their leaves and set terminal buds before the advent of cold 

 weather. Hybrid trees with U. pumila as one parent are believed to 

 have considerable promise for windbreak and ornamental purposes 

 in the area. 



Zelkova serrata. — Testing of this species was confined to the Mandan 

 station. Some winter injury occurred each year but was severe in 

 the drought years of 1934 and 1936 only. Young trees of the species 

 are highly susceptible to rabbit injury. The species has some promise 

 for windbreak planting in the area. 



Zelkova sinica. — Testing of this species was confined to the Mandan 

 station. Some winter injury occurred in most years and was severe 

 following a heavy freeze in September 1942. The data indicate that 

 the species is suitable for planting in the area. 



RECOMMENDED SPECIES 



Tree and shrub species recommended for planting on the northern 

 Great Plains must be highly resistant to long periods of freezing- 

 weather, during which time the temperature may sometimes drop 

 to as low as —63° F. A very limited amount of moisture is usually 

 available to species in dry-land plantings. In some years the total 



