PRODUCTION ASSUMPTIONS 



Assumptions Based on a Soil Survey 



Production assumptions were garnered from one na- 

 tional source — the RPA management scenario — and local 

 sources — National Forests' environmental statement and 

 a soil survey. 



National RPA Assumptions 



The RPA management scenario prepared for the pinyon- 

 juniper ecosystem described four productivity classes sub- 

 divided by condition class and range management strategy 

 (table 3). A copy of RPA management scenarios and as- 

 sumptions is on file at the Forestry Sciences Laboratory, 

 Boise, ID. The management strategy of the Oak Creek 

 area was similar to strategy D of the scenario. This con- 

 sisted of intensive management to increase livestock forage 

 consistent with constraints of maintaining the environ- 

 ment and providing for multiple use. Practices such as 

 pinyon-juniper removal and seeding with forage species 

 were a part of this strategy, as were the installation of 

 fencing and water developments to obtain a more uniform 

 distribution of livestock. 



No definition or description of the condition classes was 

 provided in the scenerio. Desirable perennial forage plants 

 on the study sites before treatment made up only 13 to 40 

 percent of the herbage and shrub production, and the den- 

 sity of the tree stand limited the herbage and shrub under- 

 story production to about 100 lb per acre. 



Assumptions for National Forests 



In the chaining environmental statement, the assump- 

 tion for change in herbage ("forage") production was an 

 increase of 500 to 700 lb per acre "under favorable condi- 

 tions" on National Forests in Utah after removal of pinyon- 

 juniper stands (USDA 1973). 



Table 3 — RPA assumptions for herbage and shrub productivity for 

 the D level management strategy 



Productivity 



Condition 



Pounds per 



class 



class 



acre per year 



1 High 



1 Good 



1,200 





2 Fair 



1,100 





3 Poor 



1,000 





4 Very poor 



800 



2 Mod. high 



1 



1,000 





2 



900 





3 



800 





4 



700 



3 Med. low 



1 



700 





2 



600 





3 



500 





4 



400 



4 Low 



1 



300 





2 



200 





3 



100 





4 



100 



A contract soil survey report prepared for the Forest 

 Service provided estimates of potential vegetation produc- 

 tivity (Stoneman and others 1979). The production of air- 

 dry vegetation in pounds per acre was estimated for both 

 unfavorable (less than average precipitation) and favorable 

 (greater than average precipitation) years. The soils of 

 three study areas had similar estimated herbage and 

 shrub productivity — 660 lb per acre in unfavorable years 

 and 1,415 lb per acre in favorable years. The estimates for 

 the Clay Springs area were less — 460 and 780 lb/acre — 

 apparently because of the sandy eolian soils that were 

 poorly developed and excessively drained. 



VEGETATION TREATMENT 



The three most recent vegetation treatments were simi- 

 lar in that the trees were removed by pulling an anchor 

 chain between two crawler tractors and the areas were 

 seeded from the air. The areas were chained a second time 

 to cover the seed and to improve the effectiveness of tree 

 removal. 



The seed mixture for the Church Hills chaining was: 



Crested wheatgrass (Agropyron 



cristatum and A desertorum) 2.0 lb per acre 



Intermediate wheatgrass 



(A intermedium) 0.6 

 Pubescent wheatgrass 



(A trichophorum) 0.6 

 Russian wildrye (Elymus 



junceus) 1.2 

 Hard sheep fescue {Festuca 



ouina ssp. duriuscula) 0.2 

 Ladak alfalfa {Medicago 



sativa var. ladak) 1.2 

 Yellow sweetclover 



(Melilotus officinalis) 0.2 

 Small bumet 



{Sanguisorba minor) 2.0 



Total 8.0 lb per acre 



A small amount of bitterbrush (Purshia tridentata), 

 cliffrose (Cowania mexicana), and fourwing saltbush 

 (Atriplex canescens) seed was also applied by dribblers 

 on the crawler tractors during the second chaining. 

 The seed mixture for the Clay Springs chaining was: 



Crested wheatgrass 2.6 lb per acre 



Intermediate wheatgrass 4.0 



Pubescent wheatgrass 1.5 



Russian v*dldrye 0.8 



Smooth brome {Bromus inermis) 2.9 

 Indian ricegrass (Oryzopsis 



hymenoides) 0.1 



Total 11.9 lb per acre 



3 



