Effects of Rest Following Defoliations on the Recovery of Several Range Species

Abstract

Seven range species, western wheatgrass (Agropyron smithii), blue grama (Bouteloua gracilis), fourwing saltbush (Artiplex canescens), antelope bitterbrush (Purshia tridentata), fringed sagewort (Artemisia frigida), scarlet globemallow (Sphaeralcea coccinea), and little rabbitbrush (Chrysothamnus vicidiflorus) were heavily defoliated once to remove 90% of the foliage during each of four different phenological stages. Defoliation effects were evaluated in the fall after the defoliated plants had received from 14 to 26 months of rest. Western wheatgrass, little rabbitbrush, and scarlet globemallow made good recovery in herbage yield, vigor, and total nonstructural carbohydrates (TNC) after a single heavy defoliation followed by 14 to 26 months of rest. Vigor and TNC levels of defoliated blue grama plants were similar to those of the control plants after the rest period, but the rest period was insufficient for the recovery of herbage yield. Herbage yield, vigor, and TNC levels of antelope bitterbrush and fourwing saltbush plants were still less than those of the control plants after the rest period when plants had been previously defoliated during the seed shatter or near maturity phenological stage. A 14- to 26-month rest period was insufficient for complete recovery of herbage yield, vigor, and TNC levels of fringed sagewort subjected to a single heavy defoliation at any phenological stage. After 26 months of rest, antelope bitterbrush and fourwing saltbush previously subjected to three heavy defoliations during quiescence, fruit developing, and fall regrowth showed some recovery. However, six heavy defoliations were detrimental and plants made little recovery in herbage yield, vigor, and TNC even after more than 2 years of rest. Blue grama plants that received three heavy defoliations made fair recovery after 2 years of rest. However, more than 2 years of nonuse would be necessary before blue grama plants subjected to six heavy multiple defoliations could completely recover. Scarlet globemallow subjected to either three or six heavy defoliations and then given 26 months of rest had herbage yields, vigor, and TNC levels that were fairly similar to that of the control plants.