Influence of forest site on total nonstructural carbohydrate levels of pinegrass, elk sedge, and snowberry

Abstract

Seasonal trends in total nonstructural carbohydrates (TNC) were studied in pinegrass (Calamagrostis rubescens Buckl.), elk sedge (Carex geyeri Boott), and snowberry (Symphoricarpos albus (L.) Blake) in western Montana in 1983 and 1984. Plants were collected from 4 forest sites at approximate 2-week intervals throughout the growing season. The sites were a clearcut and forested area in 2 different habitat types. Total nonstructrual carbohydrates were determined using an enzyme digestion technique and acid hydrolysis. Total nonstructural carbohydrates in pinegrass rhizomes exhibited a U-shaped curve with reduced levels during growth initiation in the spring and increased levels after growth cessation in late summer. Snowberry root crown TNC exhibited a V-shaped curve with rapid drawdown caused by spring growth followed by rapid replenishment of TNC levels. Elk sedge, an evergreen, did not have a stage of development which resulted in large fluctuations in TNC content of roots or root crowns. In general, TNC levels in elk sedge roots and root crowns and snowberry root crowns were greater on forested sites than clearcuts while the opposite was found in pinegrass rhizomes. Phenological development of plants growing under the forest canopy was delayed by 2 to 3 weeks compared to plants growing in the clearcuts. The influence of clipping pinegrass and elk sedge to a 5-cm or 10-cm stubble height in late May and late June was also studied. Elk sedge TNC levels were least affected when plants were clipped to a 10-cm height in late May and most affected when clipped to a 5-cm height in either May or June. Pinegrass rhizome TNC levels were lower than controls 2 weeks after clipping to 5-cm stubble heights in late May and late June, but after 4 weeks TNC levels of 5-cm clipped plants were not different from controls. Clipping to a 10-cm stubble height in late May did not cause a reduction in TNC levels. The 10-cm clipping treatment reduced pinegrass rhizome TNC levels compared to the control 2 weeks after clipping in late June. The replenishment of TNC reserves of elk sedge and pinegrass to moderate foliage removal during the spring suggests that these species may be moderately grazed in early spring when they are more palatable to livestock.