Fire, growth and survivorship in a Neotropical savanna grass Andropogon semiberbis in Venezuela

Abstract

This study was conducted in a woodland savanna in western Venezuela exclosed from grazing and burnt once a year towards the end of the dry season. Mean annual rainfall is 1500 mm, with a strong seasonality.Two cohorts of seedlings of Andropogon semiberbis were tagged and monitored for up to three years. Several variables such as survivorship, plant size, seedling density, fire damage and distance to the nearest adult were measured or estimated. Two burning experiments to measure survivorship before and after fire, and two seedling-growth experiments to assess competitive interference from adult plants of three grass species were performed.The highest mortality takes place during the dry season and is due to fire. This decreases as the plants get bigger due to increasing structural complexity of the clump by growth which gives added protection to the meristems. Other mortality factors such as desiccation, uprooting and shading seem to be important during the wet season, when mortality rate is relatively constant. Survivorship during the first year and after three years is strongly correlated to the size attained by the end of the first growing season.Seedling densities are rather low and do not seem to play any role in survivorship in this population. Adult interference with seedling growth decreases with distance and seems to be due to root competition, although there is a tendency toward increased foliage interference related to the canopy structure of adult plants.

Effect of fire regimes on the demographic parameters of the perennial tussock grasses of a humid savanna

“…Grass mortality decreased with tussock circumference irrespective of the fire treatment and the species showing that small individuals are more likely to die than larger ones, as reported by other studies that considered basal diameter as a measure of size for grass tussocks (Garnier & Dajoz, ; O'Connor, ; Silva, Raventos, & Caswell, ). Overall, this confirms that the size of plant individuals allows predicting their fate (Silva & Castro, ). The causes of the death of tussocks are not precisely identified but, most probably, small tussocks are more vulnerable to accidents (e.g.…”

Adaptive strategies in burned subtropical grassland in southern Brazil

“…The majority of the caespitose grasses found in the study on Morro Santana also occur in the Brazilian Cerrado, including most of the dominant species (e.g., Andropogon lateralis, Leptochoryphium lanatum, Elyonurus muticus). Tussock grasses present densely packed basal shoots that allow for survival of fire despite aboveground location of meristems (Gill 1981); young plants, however, may be seriously affected by fire in their survival (e.g., Silva and Castro 1989). Some tussock grasses depend on regular burns on the long run: without periodic removal of biomass through fire, shading by dead biomass inhibits survival and tillering and higher humidity under the litter may cause death and decay of underground plant parts within a few years (e.g., Bond et al 2003;Morgan and Lunt 1999;Silva et al 1990Silva et al , 1991Vogl 1974).…”

Alternative fire resistance strategies in savanna trees

“…Even for forests, studies addressing the question of ®re resistance of individual trees are rare (Gill and Ashton 1968;Vines 1968;Uhl and Kauman 1990). Most studies usually deal with seed germination (Auld and O'Connell 1991;Ernst 1991;Moreno and Oechel 1991b;Pierce and Cowling 1991;GranstroÈ m and Schimmel 1993;Lamont et al 1993;Tyler 1995), tree survival (Moreno and Oechel 1991a;Glitzenstein et al 1995), or resprouting (Gratani and Amadori 1991;Kauman 1991;Ab Shukor 1993;Morrison 1995), and grass recovery (Silva and Castro 1989;Robberecht and Defosse 1995).…”