Effects of Single and Sequential Defoliations on the Carbohydrate Reserves of Four Range Species

Abstract

Four range species, fourwing saltbush (A triplex canescens), antelope bitterbrush (Purshia tridentata), scarlet globemallow (Sphaeralcea coccinea), and blue grama (Bouteloua gracilis) were defoliated heavily (removing 90% of the foliage) at 1 of 5 phenological stages. In addition, other plants were clipped from 1 to 6 times at 3 phenological stages over a 2-year period. Total nonstructural carbohydrate (TNC) reserves of fourwing saltbush and antelope bitterbrush were most sensitive to a single defoliation at the seedshatter phenological stage. Blue grama was affected most at the rapid growth stage, whereas scarlet globemallow was not significantly affected by any of the single defoliations. A single defoliation proved adequate for determination of the most sensitive season for defoliation. Antelope bitterbrush was affected more by 6 successive intense defoliations than were the other 3 species: scarlet globemallow < blue grama < fourwing saltbush. TNC reserve cycles were severely dampened in antelope bitterbrush, and less so in fourwing saltbush. A number of early studies on rangeland plants of the arid and semiarid western USA established that carbohydrate reserves were related to the intensity, frequency, or season of defoliation (Sampson and McCarty 1930, Graber 1931, Bukey and Weaver 1939, Hanson and Stoddart 1940, McCarty and Price 1942, and Mcllvanie 1942). Albertson et al. (1953) found that root weights of 2 shortgrass prairie range plants, including blue grama, were depressed by clipping close to the ground. Crider (1955) demonstrated that harvesting half or more of the foliage from a grass plant caused root growth to stop for 6 to 18 days, and removing 90% of the foliage stopped root growth for 17 days. Blaisdell and Pechanec (1949) found that herbage removal is most injurious after the date when substantial regrowth is impossible and before maturity. De Bano (1957) showed that season of clipping affected the vigor of desert range plants more than did intensity of clipping. We initiated this study to provide information on the effect of season of defoliation on 4 range species, and document the timing and magnitude of the departure of the total nonstructural carbohydrate (TNC) cycle of heavily defoliated plants from those of control plants.