116 MISC. PUBLICATION 43 4, U. S. DEPARTMENT OF AGRICULTURE 



the trees are defoliated in early summer by insects, the large plant 

 still has enough reserve of food left in the roots to put out a second crop 

 of leaves, whereas small plants may not have the necessary reserve 

 and will suffer severely from a single defoliation. 



On the basis of field survival obtained in the experiment and a 

 knowledge of caliper-weight relationships for the various species, 



CALIPER 

 (1/16 inch) 



HEIGHT 

 (inches) 



SPECIES 



WILDING COTTONWOOD 



12-18 

 18-24 

 18-24 

 24-36 



2 a under 

 2 8t under 



2 



2 



3 



3 



4+ 



4+ 



4+ 



Under £ 

 8-12 



Under 8 

 8-12 

 8-12 

 12-18 

 18-24 



TEXAS WALNUT 



2 



3 



3 



3 

 4-5 

 4-5 

 4-5 



6 + 



6+ 



6 + 



Under 8 

 Under 8 

 8-12 

 12-18 

 12-18 

 18-24 

 24-36 

 24-36 

 36 + 



BLACK LOCUST 



60 80 100 



SURVIVAL (PERCENT) 



Figure 44. — Relation of caliper and height class to first-year survival of six 

 species of nursery stock in a drought year, in sandy soil only. 



grading recommendations have been set up for 14 species as shown in 

 table 25. Survivals to be expected of the premium grades in average 

 years are 70 to 99 percent; of the marginal grades, 40 to 70 percent; 

 and of the culls, 5 to 40 percent. In years of normal rainfall the grades 

 here classed as marginal would probably have good survival, but to 

 get consistently high first-year survivals most of the nursery stock 

 should fall in the premium grade. If it is necessary in years of low 

 nursery production to use a certain percent of trees in the marginal 

 grades, only the larger seedlings should be used, and success will then 

 depend upon exceptionally favorable moisture conditions in the field. 



