Multiple Defoliation Effects on Herbage Yield, Vigor, and Total Nonstructural Carbohydrates of Five Range Species

Abstract

Western wheatgrass (Agropyron smithii), blue grama (Bouteloua gracilis), and fourwing saltbush (Atriplex canescens) were subjected to multiple defoliations at moderate and heavy intensities during a 2-year period. Most heavy defoliation treatments drastically reduced herbage yield, vigor, and total nonstructural carbohydrates (TNC) of western wheatgrass. Multiple defoliations were detrimental to vigor and herbage yield of blue grama; however, defoliation treatments did not detrimentally affect root TNC levels. All defoliation treatments severely reduced the number of seedstalks, live crown cover, and TNC of fourwing saltbush, but seedstalk length and live crown diameter were less affected by the defoliation treatments. Both fringed sagewort (Artemisia frigida) and antelope bitterbrush (Purshia tridentata) subjected to two moderate defoliations during quiescence and rapid growth (or flowers developing) remained in fair to good vigor at the end of the growing season. However, both species were detrimentally affected if utilized during the later part of the growing season. Defoliation effects were generally more severe when plants were defoliated at a heavy intensity than when defoliated at a moderate intensity during the same phenological stages. Five- and six-pasture rest-rotation grazing systems were proposed to ensure that grazed plants would receive rest following critical late summer foliage utilization.