Silvicultural proposals modify the canopy openness to stimulate seedling growth through the changes in light and soil moisture availability. Their survival depends on their adaptation to these new stand conditions. The objective of this study was to evaluate seedling productivity in light and soil moisture gradients, along one growing season, under light, soil moisture and air temperature controlled conditions. Forest seedlings (2-3 years old) in plastic pots were placed in a greenhouse, where three light levels were assayed: 4%, 26% and 64% of the natural incident light; and two soil moisture levels: 40-60% and 80-100% of field capacity. Foliar area, total and each component biomass (leaves, stems, thin and thick roots), above/belowground biomass rate and foliar area/biomass rate were monthly measured. Total and compartmentalized biomass, foliar area and their rates significantly varied among months, soil moisture and light gradients. Towards the end of the growing season, biomass was higher in high light and low soil moisture (1.58 g plant–1) compared to high soil moisture levels (0.49 g plant–1). Aboveground biomass was significantly higher under medium light treatment (0.30 g plant–1 vs. 0.12-0.26 g plant–1), while belowground biomass increased with light (0.20 g plant–1 vs. 0.07-0.16 g plant–1). Seedlings modified their above- and below-ground biomass according to soil moisture and light conditions, producing lower rates of biomass and foliar area under the higher light treatments. The different silvicultural proposals must consider their influence over both factors (light and soil moisture) to maximize the above- and below-growth potential of the natural regeneration.