Tamaulipan thornscrub, the native vegetation type of northeast Mexico, has been severely fragmented for agriculture and induced grasslands for cattle grazing. Remnant fragments vary in size from a few hundred hectares to isolated trees. For a given individual tree, conditions vary from growing inside native vegetation to growing isolated inside agricultural fields or induced grasslands with varying degrees of competition, pollinators, and seed dispersers, which may influence individual reproductive fitness. In this study, we determined fruit and seed production as well as early seedling establishment for 10 trees inside thornscrub fragments and for 10 trees surrounded by agriculture. We found that the isolated trees produced more fruits and seeds than those inside native vegetation. The number of seedlings was, however, similar under both conditions, perhaps because of differential seed and survival mechanisms. Isolated trees seem capable of promoting tree encroachment in previously cleared habitats.