CaldLn (Prosopis cd&n& Burk.) is one of the woody species that is increasiag 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 caldkn under grazed-low herbaceous follar cover, and ungrazed-intermediate and ungrued-high herbaceous follar cover. Seedling emergence was recorded weekly after 3 plantig dates: October 1987, September 1988, and October 1989. SeedUng survival was recorded every 2 weeks until all seedlings died. Precipitation, soil water potential, and soil temperature were monitored during the study period. Since caldLn only reproduces from seeds, optimal conditions for gennlnation under different controlled photoperlod and temperature regimes were also studied. In the laboratory, greatest germination of freshly harvested unscarifled seeds occurred at a diurnally alternating temperature regime of 15 and 300 C with light provided for 9 hours. Least germination occurred at 150 C and continuous darkness. Acid scarlficatlon 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 grazedlow herbaceous cover site. Only for 1987 data, emergence was greater on the grazed area with relatively low herbaceous follar 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 caldbn seedling mortality was always coincident with higher soil temperature and lower soil water availability.

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