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

Four range species, fourwing saltbush (Atriplex 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 seed-shatter 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.