Fire Effects on Bud Viability and Growth of Stipa tenuis in Semiarid Argentina

Abstract

Numbers of total, metabolically active, dormant or dead axillary buds, and growth characteristics were determined before and after controlled burnings in Stipa tenuis Phil., a native forage grass of the Caldén District in central Argentina. One-hectare plots were burned on 25 Mar. (Burn 1) or 4 Apr. 1991 (Burn 2), or remained unburned (control). Bud metabolic activity was examined using the tetrazolium test and the vital stain Evans' blue.Before fire, more than 83% of the axillary buds on previous-season stems of S. tenuis were metabolically active in all treatments. After fire, previous-season stems that produced tiller in the control and Burn 2 plots had more than 75% of the axillary buds alive, but those that did not produce them had more than 82% of their axillary buds dead in the burned areas. This high bud mortality was associated with direct fire effects on the fate of buds; most dead buds showed visible signs of dehydration. Since more than 97% of the plant stem bases did not produce tillers after fire, tiller number per plant was reduced (P < 0·05) in the burned plots to fewer than 22% of values of controls. Plant mortality was 50% higher at the Burn 1 than at the Burn 2 site probably because the first site had a 43% lower soil moisture content (P < 0·05). At the end of the growing season, however, a different set of S. tenuis plants at both burned sites had a similar tiller number and dry weight to controls. These plants were probably in areas of lighter fuel loads and exposed to a less intense fire.