R.M. Bóo

Emergence and seedling survival of calden in the semiarid region of Argentina.

Calden (Prosopis caldenia Burk.) is one of the woody species that is increasing in abundance due to poor grazing management in the semiarid region of central Argentina. The objectives of this work were to evaluate emergence and seedling survival of calden under grazed-low herbaceous foliar cover, and ungrazed-intermediate and ungrazed-high herbaceous foliar cover. Seedling emergence was recorded weekly after 3 planting dates: October 1987, September 1988, and October 1989. Seedling survival was recorded every 2 weeks until all seedlings died. Precipitation, soil water potential, and soil temperature were monitored during the study period. Since calden only reproduces from seeds, optimal conditions for germination under different controlled photoperiod and temperature regimes were also studied. In the laboratory, greatest germination of freshly harvested unscarified seeds occurred at a diurnally alternating temperature regime of 15 and 30 degrees C with light provided for 9 hours. Lead germination occurred at 15 degrees C and continuous darkness. Acid scarification significantly increased germination percentage and germination rate. Unscarified seeds incubated in light exhibited a lower rate of germination than scarified seeds under all temperatures. In the field, soil water availability was usually similar among the 3 experimental conditions. Soil temperature was only occasionally higher in the grazed-low herbaceous cover site. Only for 1987 data, emergence was greater on the grazed area with relatively low herbaceous foliar cover and similar within the ungrazed area. Treatment effect was very little on seedling survival, being lower in the grazed area for only 2 evaluation dates in 1989. Regardless of treatment the emerged seedlings survived 40 days on the average. The highest calden seedling mortality was always coincident with higher soil temperature and lower soil water availability.

Botanical composition of cattle and vizcacha diets in central Argentina.

Cattle (Bos taurus) and vizcacha (Lagostomus maximus) diets were examined monthly in the semiarid Caldenal in central Argentina. Cow-calf operations are the most important economic activities within the region. In spite of a widespread distribution of the vizcacha in Argentina, comparative studies of the diet of cattle and vizcacha are scarce. The objective of this work was to analyze the botanical composition, seasonal trends, and possible dietary overlap between cattle and vizcacha. Diets were determined by microscopic analysis of cattle and vizcacha feces collected from November 1994 through December 1995 in a shrubland community of the southern Caldenal. Grasses were the bulk of the diet for both herbivores. Piptochaetium napostaense (Speg.) Hack. was the most abundant grass in vizcacha (53%) and cattle (40%) diets. Prosopis Caldenia Burk. pods partially (34%) replaced this grass in cattle diets during late summer and fall. Consumption of P. napostaense was generally higher (13%) in vizcachas than in cattle, especially during the dry period of the study (21%). During the drier months, cattle consumed more of the less preferred grasses (48%). Forbs were poorly represented in the diets perhaps because of scarce rains and low availability. Classification and ordination techniques revealed seasonal trends and overlapping diets. A greater overlap (75%) was found during the wet period due to simultaneous consumption of P. napostaense by both herbivores. Trends in diet diversity were similar with indices generally higher for cattle than for vizcachas, especially during the dry period.

Effect of fire on growth of three perennial grasses from central semi-arid Argentina

Abstract The effect of fire on growth of Piptochaetium napostaense , Stipa tenuis , and Stipa gynerioides , three important native perennial grasses in the semi-arid region of central Argentina, was evaluated under different fire temperature regimes: 300–400°C (low temperature regime), 500–600°C (high temperature regime) and no fire (control). Fire treatments were applied with a portable propane plant burner in April and December 1994, May 1995, and January 1996. Overall results indicate that during the first months after fire occurrence, average total green length of S . tenuis , P . napostaense and S . gynerioides tillers was severely reduced ( p P . napostaense , S . tenuis , and S . gynerioides were similar or greater ( p S . tenuis , P . napostaense and S . gynerioides were greater than in tillers of control plants. Our results indicate that fire affected differentially the growth of the studied species; S . gynerioides was more affected by fire than P . napostaense and S . tenuis . The species most tolerant to fire was P . napostaense .

Plant water potential for shrubs in Argentina.

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