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In semi-arid environments, the distribution of rainfall over time is decisive in emergence in a soil seed bank. The objective of this work was to evaluate the effect of rainfall events on the soil seed bank emergence of Caatinga species under high CO 2 concentration. The experiment was carried out in an experimental area of Embrapa Semi-arid in a randomized complete block design, with subdivided plots. Each plot consisted of different environmental conditions (open top greenhouse with injection of 550 ppm CO 2 ; open top greenhouse and environmental CO 2 ; natural environment). The subplots consisted of the depth at which the seeds of Poincianella pyramidalis and Myracrodruon urundeuva were sown (superficially and buried at 0.02 m and 0.06 m depth). Seedling emergence was monitored daily after the first rains. During the experiment, weather data showed a rainfall volume of 83 mm, an average air temperature of 28.7 o C, average soil temperature of 35.4 e 34.9 o C, at depths of 0.02 and 0.06 m, respectively. Seedling emergence started 56 days after sowing and 4 days after the first rains. After 154 days of the start of the experiment, drip irrigation was performed. The greenhouse environment, regardless of the addition of CO 2 or not, allowed higher emergence percentage of P. pyramidalis . The seeds of this species sowed on the soil surface only emerged when irrigation started. M. urundeuva seeds showed low germination even after irrigation.