FIRE EFFECTS ON BUD VIABILITY AND GROWTH OF STIPA-TENUIS IN SEMIARID ARGENTINA

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 Calden 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 tillers 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. © 1993 Annals of Botany Company.