Global environmental changes are affecting tree population demography with potentially significant impacts on forest biodiversity and wood industry. Forest regeneration processes include seed production, growth and survival of saplings to the recruitment sizes at which trees are considered in forest inventories. Changes in regeneration dynamics directly affect forest composition and structure and can jeopardize the sustainability of forest management. This is especially the case in mountain forests where environmental gradients are strong and where forests are often uneven-aged, i.e. combining trees of all ages in a single stand. Regeneration processes are difficult to monitor. Large data sets often give only fixed pictures of sapling densities with little information on demographic processes. In this thesis, we quantified the effects of different biotic and abiotic factors on regeneration dynamics of Picea abies (spruce), Abies alba (fir) and Fagus sylvatica (beech) in the French Alps and Jura mountains. We also predicted changes in tree recruitment fluxes in these forests, for potential climate change situations. We recorded sapling height increment and density of spruce, fir and beech in 152 plots across the French Alps and Jura mountains. We then analysed how biotic and abiotic factors known to affect regeneration, namely altitude, slope, aspect, light availability, soil characteristics, ungulate browsing, temperature, precipitation and evapotranspiration, affected sapling density and growth using non-linear mixed models. We showed that temperature has a positive non-linear effect on sapling height growth and water resource availability has a positive effect on sapling density. Terminal shoot browsing, which prevents sapling height growth, is especially frequent on fir. In a second analysis, we built a more comprehensive model of regeneration dynamics, representing explicitly the process of new seedling production, sapling growth, browsing and survival, and finally their recruitment into adult trees. We predicted parameters for these processes in combination, using Approximate Bayesian Computation (ABC), based on the field data collected earlier. The results imply that more frequent and intense heat and drought events could negatively influence sapling growth and survival of the three species, with probable reduction of forest renewal fluxes. An increase of ungulate populations leading to increased browsing could be especially detrimental to fir and possibly also to beech saplings. We also predicted the potential tree recruitment fluxes for different IPCC climate projection scenarios for the year 2100, and showed that a reduction in tree recruitments is highly likely. This study shows that the ABC method can be efficiently used to estimate regeneration dynamic processes, based on sapling density, height increment and browsing data. It highlights the vulnerability of future forest regeneration to water availability and ungulate presence, urging researchers and forest managers alike to anticipate future potential important changes in mountain forest dynamics.