Skip to main content
ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #120780
Title: DROUGHT AND GRAZING: IV. EFFECTS ON BLUE GRAMA AND WESTERN WHEATGRASS TILLER DYNAMICS

Author
item ENEBOE, ERIC - NRCS
item SOWELL, BOK - MONTANA STATE UNIVERSITY
item Heitschmidt, Rodney
item KARL, M - BLM
item Haferkamp, Marshall

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2001
Publication Date: 3/1/2002
Citation: ENEBOE, E.J., SOWELL, B.F., HEITSCHMIDT, R.K., KARL, M.G., HAFERKAMP, M.R. DROUGHT AND GRAZING: IV. EFFECTS ON BLUE GRAMA AND WESTERN WHEATGRASS TILLER DYNAMICS. JOURNAL OF RANGE MANAGEMENT. v. 55. p. 197-203. 2002.

Interpretive Summary: The broad objective of this research was to determine the effects of grazing during and immediately following drought on rangeland forage productivity and plant species composition. The specific objective of this research was to examine these effects as they relate to the tiller growth dynamics of western wheatgrass and bluegrama, two of the dominant grasses growing in the Northern Great Plains. Tiller growth dynamics were selected for study because differences among plants in tiller growth rates is a fundamental cause for changes in plant species productivity and composition. Study was conducted using an automated rainout shelter that controlled amount of precipitation received on drought treatment plots. The 5-month drought was imposed from late May to mid-October of 1994. Study results were somewhat less dramatic than expected because: 1) a "natural" drought occurred on the non-rainout shelter control plots during the imposed drought; and 2) the drought was imposed during the latter portion of the normal growing season. Thus, neither drought nor grazing either during the year of or the year after the imposed drought affected plant species composition. Likewise, neither drought nor grazing treatment affected the productivity of blue grama at any time although both drought and grazing reduced western wheatgrass production but then only during the year of drought or grazing. Therefore, we concluded that moderate levels of grazing during a mid- to late growing season drought or during the year after such a drought will have minimal long-term impacts on either bluegrama or western wheatgrass productivity.

Technical Abstract: An understanding of the impacts of grazing during and following drought on rangeland ecosystems is critical for developing effective drought management strategies. This study was designed to examine the effects of drought and grazing on blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] and western wheatgrass [Pascopyrum smithii Rydb. (Love)] tiller growth dynamics. Research was conducted from 1993 to 1996 at the Fort Keog Livestock and Range Research Laboratory located near Miles City, Mont. An automated rainout shelter was used during 1994 to impose a severe late spring to early fall (May to October) drought on 6 of twelve 5 X 10-m non- weighing lysimeters. Twice replicated grazing treatments were: 1) grazed both the year of (1994) and the year after (1995) drought; 2) grazed the year of and rested the year after drought; and 3) no grazing either year. Drought had minimal impact on tiller relative growth rates of plants which were grazed twice, although it reduced (P < 0.01) rates of axillary tiller emergence for blue grama (79%) and western wheatgrass (91%), respectively. Defoliation periodically increased relative growth rates (P < 0.05) and tiller emergence (P < 0.01) of both species. Neither drought nor grazing affected tiller densities or tiller replacement rates of either species nor did they affect productivity of blue grama. Drought, however, reduced (P < 0.01) productivity of western wheatgrass 50% in 1994 whereas grazing reduced productivity (P < 0.01) by 46% in 1994 and 69% in 1995. Moderate stocking levels (40-50% utilization) during and after drought did not adversely affect the sustainability of these dominant native grasses.