Resumo. Climate change is currently part of the agenda in scientific debates and of interest in forest sciences, but studies of vulnerability of cultivated forest species to climate change are rare. The objective of this study was to simulate the duration of the seedling phase in two eucalyptus species (Eucalyptus saligna and Eucalyptus grandis) in elevated temperature scenarios at Santa Maria, RS, Brazil, considering several emergences dates. The seedling phase was considered from the emergence of the seedlings until the appearance of the 25th leaf on the main stem. Leaf appearance rate (LAR) was estimated using a multiplicative model with a non-linear response function of LAR to daily mean air temperature, with coefficients for the species Eucalyptus saligna and Eucalyptus grandis. Twelve emergence dates (day 15 of each month of the year) and six climate scenarios (current, +1°C, +2°C, +3°C, +4°C, and +5°C) were considered. The Climate scenarios are made up of synthetic series with one hundred years of daily minimum and maximum air temperature synthetic series. The LAR model was run in each year of the climate scenarios for each emergence date and species, and the number of days from emergence to the appearance of the 25th leaf was counted (seedling phase duration). Statistical analysis consisted of analysis of variance for the variable duration of the seedling phase, assuming a three-factor experiment (Factor A= six climates scenarios, Factor B= twelve emergence dates, Factor C= two species) in a completely randomized design, with each year of simulation as a replication. The results indicated a reduction of the seedling phase duration in the warm climate scenarios for emergences from March to September, and a increase in the duration for emergences from October to February and on an annual basis, the increase in temperature leads to a decrease in time of seedling in a nursery and thus increases the annual seedling production of Eucaliptus. However, low seedling vigor and disease related problems may increase, mainly during summer. Benefits and disadvantages of these results should be considered in policies for mitigating the effects of global warming in silviculture.