Response of Grass Species to 

 Tree Harvesting in Singieieaf 

 Pinyon-Utaii Juniper Stands 



Richard L. Everett 

 Steven i-l. Sharrow 



r 



INTRODUCTION 



An inverse relationship between tree cover and forage 

 production is well established for severEil forest systems 

 including the pinyon-juniper woodlands of the West 

 (Jameson 1967; Clary 1969). Thinning or clearcutting 

 small patches of trees has been suggested to increase 

 production and quality of forage for wildlife and live- 

 stock (Patton 1974), but cutting must be balanced with 

 the appropriate management of the wood resource. Cur- 

 rently little is known about understory response follow- 

 ing tree harvest in the pinyon-juniper woodlands of the 

 Great Basin. Understory production has increased fol- 

 lowing removal of juniper species in the Southwest, but 

 there are large variations due to soils and climate 

 (Jameson and Dodd 1969; Clary 1974). 



Understory species composition and cover vary among 

 soil microsites found within pinyon-juniper stands 

 (Harner and Harper 1976; Everett and Koniak 1981). 

 Understory composition and distribution patterns are 

 closely tied to tree cover and associated soil characteris- 

 tics (Everett and others 1984). Barth (1980) demon- 

 strated nutrient enrichment in soil microsites under the 

 tree crown of pinyon (Pinus edulis Engelm.) and the 

 depletion of nutrients from the interspace microsites 

 among tree stems. 



Understory production, protein levels, and mineral con- 

 centrations may increase under the crowns of semiarid 

 shrubs in response to increased soil nutrients and shad- 

 ing effects (Rickard and others 1973). Under mesic forest 

 conditions, forage production and digestibility may de- 

 cline with increasing overstory cover, but protein concen- 

 trations may increase (Laycock and Price 1970). Climate 

 of the singieieaf pinyon {Pinus monophylla Torr. and 

 Frem.)-Utah juniper (Juniperus osteosperma [Torr.] 

 Little) woodland is intermediate between these two vege- 

 tation types, and forage quality and quantity differences 

 among soil microsites are unknown. 



Microsites that produce more nutritious forage are 

 particularly important to selective feeders like deer 

 (Odocoileus sp.) that must depend on high quality forage 

 because of their limited rumen capacity (Hartley 1982). 

 Utilization of forage by livestock and wildlife is directly 

 related to nitrogen and phosphorus levels in plants and 

 soils (Van Soest 1982). Increases in nutrient concentra- 

 tions of forage among soil microsites may increase in- 

 take and animal gains. 



Protein, phosphorus, and energy usually limit animal 

 nutrition on western ranges (Halls 1970; Cook and 

 Harris 1977). Ruminants feed until energy requirements 



are met or their rumen is full. Consequently nitrogen 

 and phosphorus uptake depends on their concentrations 

 in consumed forage. 



Grass yield from woodland sites is a hierarchial 

 phenomenon: (1) individual species yield, (2) composite 

 species yield by soil microsite, and (3) composite micro- 

 site yield by site. This study assessed forage quality 

 differences of grass species on tree-harvested and non- 

 harvested plots and among soil microsites that occur on 

 those plots. We chose to sample yield at plant maturity 

 and forage quality at the anthesis phenologic stage. We 

 asked: (1) What effect does tree harvesting have on in- 

 dividual species yield and nutritional quality? (2) What 

 changes in grass yield and quality occur on individual 

 soil microsites? (3) What is the total nonharvested and 

 harvested plot yield available to cow/calf pairs and wild- 

 life that use the sites? 



Change in forage quality over time has been ade- 

 quately documented for many of the grass species in 

 this study (Murray and others 1978). Although exact 

 timing of nutrient changes may differ between study 

 areas, decline in forage quality over time has been suffi- 

 ciently established in the literature to have already been 

 made into a basic range management concept (Vavra 

 and Raleigh 1976), and therefore these trends need not 

 be restudied here. 



METHODS 

 Study Site 



We chose a study area with a simple floristic composi- 

 tion and sufficient grass understory to demonstrate a re- 

 sponse to tree release. The study area was a singieieaf 

 pinyon-Utah juniper woodland approximately 2.5 mi 

 (4 km) northeast of lone in the Shoshone Mountain 

 range of west-central Nevada. Similar areas occur on 

 several mountain ranges in western Nevada. 



Basalt-andesitic derived soils were classified as clayey, 

 skeletal, mixed, frigid, Lithic Xerollic Haplargids (USDA 

 1975). These soils are depleted of nutrients in the inter- 

 space between trees and are enriched under the tree 

 crowns (Everett 1984). Precipitation during the study 

 was: 



Year Inches (mm) 



1979 9.5 240 



1980 12.6 320 



1981 11.8 300 



1982 13.0 330 



1983 17.3 439 



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