RESULTS AND DISCUSSION 

 Species Yield and Plant Density 



All plant species examined showed a numerical in- 

 crease in yield on tree-harvested plots, although differ- 

 ences were not always statistically significant (table 1). 

 Except for squirreltail (west) and Idaho fescue (north), 

 the greater yield on tree-harvested plots was the result 

 of increased growth per plant and not increased plant 

 density. 



Squirreltail biomass and plant density increased on the 

 tree-harvested plot of the west aspect. The species was 

 barely represented on nonharvested plots but rapidly oc- 

 cupied the duff microsite following tree removal (Everett 

 and others 1984). Robust growth of squirreltail following 

 tree felling was previously reported by Clary and 

 Morrison (1973) for alligator juniper (Juniperus deppeana 

 Steud.) woodlands. Idaho fescue dominated the under- 

 story of the north aspect on nonharvested and tree- 

 harvested plots. 



Table 2.— Percentage in vitro digestibility of grass species on 

 tree - harvested and nonharvested plots for 1980 

 and 1981 by aspect 



1980 



1981 



Grass 



Nonharvest Harvest Nonharvest Harvest 



-Percent digestibility- 

 South 



Sandberg bluegrass 



63'' 



763 



62= 



66" 







West 







Sandberg bluegrass 



723 



723 



68^ 



67t' 



Squirreltail 



57a 



_2 



663 



563 



Junegrass 



673 





723 



59"^ 



Idaho fescue 



573 





523 



463 



North 



Sandberg bluegrass 72 72 

 Idaho fescue 603 643 



47b 



52'' 



^Dissimilar superscripts denote significant (p = 0.05) differences in 

 in vitro digestibility between harvested and nonharvested plots in 1980 

 and 1981 for a given species (same row/). 



^Inadequate plan-t materials available for sampling. 



Table 1.— Grass yield and plant density on tree - harvested 

 and nonharvested singleleaf pinyon-Utah juniper 

 plots by aspect 



Yield Density 



Grass Nonharvest Harvest Nonharvest Harvest 



Lb/acre Plants/ft^ 



South 



Sandberg bluegrass 



24.9 



26.7 



0.8 



0.6 







West 







Sandberg bluegrass 



14.3 



59.8*1 



2.1 



1.5 



Squirreltail 







274.8* 



.1 



A + 



Idaho fescue^ 



8.9 



10.7 



.1 



.1 







North 







Sandberg bluegrass 



4.5 



32.1* 



1.4 



1.3 



Squirreltail 



12.5 



13.4 



.1 



.1 



Idaho fescue 



39.3 



151.7* 



.4 



.8 + 



i( + ,*) significantly (p = 0.1, p = 0.05) greater yield or plant density 

 on tree -harvested than nonharvested plots. 



^Junegrass plants w/ere present but in too few numbers for statisti- 

 cal analysis. 



Species Forage Quality 



In vitro digestibility of grass on tree-harvested plots 

 was greater or equal to that on nonharvested plots for 

 Sandberg bluegrass and Idaho fescue (north). Digestibil- 

 ity of squirreltail, junegrass, and Idaho fescue (west) was 

 similar or lower on tree-harvested than on nonharvested 

 plots (table 2). Appeirent contradictory reports of digesti- 

 bility increasing (Duvall 1970), remaining unchanged 

 (Conroy and others 1982), or declining (Laycock and 

 Price 1970) following tree harvest appear justified. We 

 found digestibility increased and decreased among spe- 

 cies growing on the same site. A general decline in di- 

 gestibility of grasses on our sites occurred from 1980 to 

 1981. 



Based on averages of data, species digestibility was in 

 the general order of Sandberg bluegrass = junegrass > 

 squirreltail > Idaho fescue (table 2). Wallace and others 



(1961) reported a similar order for junegrass (67-69 per- 

 cent) > squirreltail (64-65 percent) > Idaho fescue (54-55 

 percent) in eastern Oregon. Gross energy estimates 

 derived from the bomb calorimeter followed a different 

 species order: squirreltail (4,150 ±50 cal/g) > junegrass 

 (4,030 ±90 cal/g) > Sandberg bluegrass (3,840 ±40 cal/g) 

 > Idaho fescue (3,640 ±270 cal/g). Idaho fescue on our 

 sites was low in both digestibility and gross energy. If 

 carrying capacity were estimated from yield data alone, 

 the estimate would be too high. 



Percentage nitrogen (N) was numerically greater for all 

 species on tree-harvested plots (table 3) and significantly 

 so for Sandberg bluegrass (£ill aspects), squirreltail (west 

 aspect), and Idaho fescue (west aspect). Minimum nitro- 

 gen (N) requirements for maintenance of a 1,100-lb 

 (500-kg) lactating cow (9.2 percent protein = 1.47 percent 

 N: National Research Council 1976) were met by all spe- 

 cies on tree-harvested sites and by squirreltail. 



Table 3.— Concentrations of percentage nitrogen and percent- 

 age phosphorus in grass species on tree-harvested 

 and nonharvested south, west, and north aspects 



Nitrogen Phosophorus 

 Grass Nonharvest Harvest Nonharvest Harvest 



Percent 







South 







Sandberg bluegrass 



1.04 



2.25 + ^ 



.12 



0.16 + 







West 







Sandberg bluegrass 



.85 



1.57* 



.09 



.15* 



Squirreltail 



1.50 



1.94 + 



.22 



.22 



Junegrass 



1.47 



1.64 



.24 



.31* 



Idaho fescue 



1.11 



1.43* 



.19 



.21 







North 







Sandberg bluegrass 



1.18 



1.95* 



.17 



.22 + 



Idaho fescue 



1.54 



1.64 



.20 



.21 



^Significant ('. + , p = 0.05, p = 0.1) differences between non- 

 harvested and harvested plots. 



3 



