Ganskopp conducted a study on the Squaw Butte Experimental Range to determine the response of containerized Thurber needlegrass (Stipa thurberiana) to single defoliations (2.5-cm stubble) throughout the growing season. Thurber needlegrass was most effected by defoliation during the early-boot stage of development with reductions of 63% and 45% in shoot and root biomass, respectively, the first year, and 38%, 34% in the second year. Overall regrowth potential declined as the season progressed and soil water content was gradually depleted. Thus, regrowth exceeded pretreatment production only when plants were clipped at the vegetative stage (first defoliation treatment). Herbage production of control plants and phenological development were similar between years, but there were differences in the "growth curve" and response to treatments (for example spring growth was not effected after the first year treatments, but was lower after the second), which may be the result of an interaction with temperature and precipitation differences between the two years of the study.
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