Some tropical countries, such as Colombia, are venturing into the international carbon market by means of avoided deforestation programs, i.e., they seek carbon credits by not cutting down forests. Consequently, basic information about carbon storage in different forest types is urgently needed. We describe the tree community dynamics of forest fragments in cattle ranches of the western Orinoco basin, and their relationship to the forests’ ability to accumulate carbon. We re-sampled three 1-ha vegetation plots after six and seven years of establishment. We found that these forests have different population dynamics; smaller fragments have negative net population change, but the dynamics allow for an annual carbon accumulation rate of around 0.57 Mg ha^–1. This rate is similar to the rate reported for some mature Amazon forests and may be attributed to high soil fertility.