Abiotic and biotic changes caused by forest fragmentation have led to the decline of many plant species. We sought to investigate how biotic (liana and bamboo cover) and abiotic (soil moisture litter depth and canopy openness) factors affect the total abundance and the numbers of individuals of Psychotria vellosiana Benth. at each stage of its life cycle (seedlings juvenile I and II adult reproductive and vegetative) in a fragmented landscape. P. vellosiana was selected because it is a forest species important for fauna especially ants and birds in the understory and is highly abundant in semideciduous Atlantic forest areas. We hypothesised that fragments with less humidity greater litter depth greater canopy openness and more liana and bamboo cover would contain fewer individuals at all five life cycle stages of that species. Ten 0.01?ha plots were set up in semideciduous Atlantic Forest fragments and all individuals of P. vellosiana were tagged and measured. The study also measured canopy openness soil moisture litter depth and bamboo and liana cover. Our results indicated that there was a negative relationship between liana and bamboo cover at all stages of the life cycle of P. vellosiana. This is one of the few studies that has investigated environmental effects on all stages of the life cycle of a plant population and demonstrates that liana and bamboo cover can affect all stages of plant growth and development. Despite some restrictions we can affirm that forest species are threatened by fragmentation processes and that the main threat to local populations of P. vellosiana is liana and bamboo cover.