Yield of dry matter, digestible dry matter, digestible 

 energy, protein, and phosphorus was greater on tree- 

 harvested than on nonharvested plots on north and west 

 aspects (table 5). Yield was similar on tree-harvested and 

 nonharvested plots of the south aspect. O'Rourke and 

 Ogden's (1969) suggestion that high tree cover is an in- 

 dication of potentially high understory production did 

 not hold in this instance (tree cover 28 percent north vs 

 54 percent south). Tree cover had not yet stabilized on 

 the north aspect (Meeuwig and Cooper 1981). The 

 reported loss in production of cool season grasses follow- 

 ing tree harvest in Arizona (Clary and Morrison 1973) 

 did not occur here. Basic climatic differences exist be- 

 tween the two woodland systems. 



The "minimal area" required to provide the daily 

 digestible energy requirement for a 1,100-lb (500-kg) lac- 

 tating cow (24.41 M cal DE: National Research Council 

 1976) utilizing 50 percent of the grass yield varied from 

 1.43 acres (0.58 ha) on nonharvested plots to 0.15 acre 

 (0.06 ha) on tree-harvested plots (T-5). A clearcut area of 



Table 5.— Yield of dry matter, digestible dry matter, digestible 

 energy, protein, and phosphorus on nonharvested 

 and tree -harvested sites for June 1981 on south, 

 w/est, and north aspects 



Aspect 



Nonharvest 



Harvest 



South 



West 



North 



South 



West 



North 



South 



West 



North 



South 



West 



North 



South 



West 



North 



South 



West 



North 



Dry matter 



Lb/acre 

 25.3 27.2 

 24.1 345.3*'' 

 55.9 197.2 + 



Digestible dry matter 



Lb/acre 

 20.1 20.4 

 18.3 202.9* 



29.8 109.9 + 

 Digestible energy 



kca I/acre * 1(P 

 36.46 35.89 



32.09 373.82 

 51.51 188.02 



Minimal grazed area^/acres/ 

 animal/day @ 50% utilization 



1.28 

 1.43 

 .89 



2.2 

 2.1 



3.0 



0.04 

 .06 

 .07 



Protein 



Lb/acre 



Phosphorus 



Lb/acre 



1.28 

 .15 

 .25 



3.2 

 37.6* 

 17.7 



0.05 

 .27* 

 .45* 



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

 harvested and harvested plots. 



^Minimal grazed area, tfiat area providing sufficient digestible 

 energy to meet ttie maintenance requirements for a 1,100-lb (500-kg) 

 lactating cow. 



4.5 to 7.4 acres (1.8 to 3 ha) would furnish 1 animal unit 

 month (AUM) of forage on the west and north aspects. 

 Nonharvested woodlands and the harvested south aspect 

 would require 26.7 to 43.0 acres (10.8 to 17.4 ha)/AUM. 

 Nonharvested singleleaf pinyon-Utah juniper woodlands 

 provide much less forage than nonharvested alligator 

 juniper woodlands— 5.4 acres (2.2 ha)/AUM (Clary 

 1974)— but harvested plot forage production is compara- 

 ble at 3.7 acres (1.5 ha)/AUM (Clary 1974) vs 4.5 acres 

 (1.8 ha)/AUM on our sites. 



Protein increased significantly following tree harvest 

 on west and north aspects but not on the south aspect. 

 If animeils grazed until they met their maintenance 

 energy requirements, protein uptake would be adequate, 

 2.0 lb (0.91 kg)/day (National Research Council 1976), on 

 north and west tree-harvested plots and the non- 

 harvested plot on the north aspect. South (0.1 lb 

 [0.05 kg] N) and west (1.3 lb [0.60 kg] N) nonharvested 

 plots and the south tree-harvested plot do not provide 

 adequate protein levels. Minimum phosphorus intake of 

 0.6 oz (17 g)/day (National Research Council 1976) would 

 not be met grazing either nonharvested (0.4 to 0.7 oz 

 [13 to 20 g]/day) or tree-harvested (0.5 to 0.9 oz [15 to 

 25 g]/day) plots. 



CONCLUSIONS 



Grass cover, yield, and nutrient content increased sub- 

 stantially following tree harvest on north and west 

 aspects, but there was minimal response on the south as- 

 pect. These results require verification on other sites. 

 South aspects should not be tree-harvested for increased 

 forage for livestock. But increased forage quality follow- 

 ing tree removal may provide improved deer habitat. 



Fully stocked woodlands provide little forage, approxi- 

 mately 42 acres (11 to 17 ha)/ AUM. This can be sub- 

 stantially increased by tree harvesting (4.5 to 7.4 acres 

 [1.8 to 3 ha]/ AUM) on more mesic aspects. In early sum- 

 mer, nitrogen levels are generally adequate for livestock 

 on tree-harvested plots but inadequate on nonharvested 

 plots. Grass on nonharvested and tree-harvested plots 

 provides inadequate nitrogen and phosphorus levels for 

 deer. 



In undisturbed stands tree competition effectively 

 equalized grass yield among soil microsites and aspects. 

 Grass production and quality increased more on tree- 

 associated microsites (duff and transition) than in the 

 interspace following tree removal. We speculate this was 

 the result of greater soil nutrients under the tree crown 

 and greater preharvest plant density adjacent to the tree 

 crown edge (Everett 1984). Selective feeders, like deer, 

 that maximize nutritional quality would benefit from the 

 more nutritious forage of tree-harvested sites and espe- 

 cially forage on tree-associated microsites. 



The lack of greater nitrogen and phosphorus concen- 

 trations in grass plants associated with overstory was at 

 variance with previous reports from more arid and mesic 

 plant communities (Duvall 1970; Rickard and others 

 1973; Holecheck and others 1981). We can only speculate 

 that overstory competitive effects are uniform across our 

 site and prohibit understory from utilizing increased soil 

 nutrients associated with the tree crown. 



5 



