^ 10 20 30 40 50 60 70 80 



SEEDED GRASS IN THE COMPOSITION, % 



Figure 1 — Relationship of percent seeded grassses 

 and total production. 



1200 I- 



1000 - 



a DC 



z u 



< < 



111 m 



1955 TREATMENT 

 1977 TREATMENT 



800 



600 - 



400 - 



200 - 



SWALE BOTTOM 



SIDE SLOPE 



RIDGE CREST 



TOPOGRAPHIC POSITION 



Figure 4 — Effect of topography on herbage and shrub 

 production. Bars represent a mean for 3 years of data. 



8 12 16 20 24 

 YEARS AFTER TREATMENT 



Figure 2 — Percent seeded grasses and year after 

 treatment. 



lOOOi- 



8 12 16 20 24 

 YEARS AFTER TREATMENT 



Figure 3 — Production time trend. 



Total production was closely correlated to the propor- 

 tion of the seeded wheatgrasses (fig. 1). This suggests 

 that many of the other plants present following tree re- 

 moval, both natives and exotics, are inefficient in the use 

 of the existing site productivity, or at least they are slow 

 in developing the densities necessary to fully utilize the 

 site. The older stands tended to be dominated by interme- 

 diate and pubescent wheatgrasses that are rhizomatous 

 and sod-formers (Asay and Knowles 1985; Wasser 1982). 

 These seeded grasses have the capability to increase 

 stand densities over time by vegetative means. The data 

 from Oak Creek suggest that about 8 to 10 years are re- 

 quired for these grasses to reach a stable proportion of the 

 composition, which may be over 80 percent (fig. 2). Simi- 

 lar to this trend, the total production of herbage and 

 shrubs appeared to increase for as much as 8 years 

 (fig. 3). Previous results from the Utah area have demon- 

 strated that the level of total herbage production in the 

 early years after seeding is strongly affected by the pro- 

 portion of seeded grass in the plant community (Clary and 

 Wagstaff 1987; Phillips 1977). 



There was a substantial difference among swale bottom, 

 side slope, and ridge crest areas of topography (fig. 4, 

 tables 5 and 6). Herbage and shrub production in the 

 swale bottom portions of the topography with its deeper 

 soil and more favorable soil moisture condition was a 

 third and two-thirds greater than the side slope and ridge 

 crest portions of the area, respectively. 



Comparison With Assumptions 



The RPA assumptions for herbage and shrub produc- 

 tion under intensive management vary from 1,200 down 

 to 100 lb per acre depending upon productivity class and 

 condition class (table 3). The older treatment areas, con- 

 sidered to represent the long-term production potential 

 for seeded stands, have a strong dominance of seeded 

 grasses and therefore were considered in "good" condition. 

 These areas (tables 5 and 6) averaged 740 lb per acre of 

 herbage and shrub production with a 95 percent 



6 



