With urbanisation rapidly transforming our world, a better understanding of how urban ecosystems can contribute to biodiversity conservation is urgently needed. Here, we investigated the functional composition and diversity of plant assemblages in different types of urban forests with the intent to predict the stability of the functions provided by these forests through the functional redundancy and response diversity of species. For this, we used data from non-urban mature forests, remnant urban forests, urban forests regenerated from croplands and urban forests regenerated from soil denudation, all located in the Brazilian Atlantic Forest. Our results showed that species functional composition shifted among urban and non-urban forests. However, functional diversity was lost only in urban forests with some previous use, indicating that the natural regeneration of urban forests after previous land use results in functionally poor forests. Urban forests regenerated from soil denudation (more intense disturbance) had a lower functional diversity. Conversely, urban forests regenerated from cropland (less intense disturbance) showed only a reduction in the number of functions provided. Our analysis also revealed the reduced functional redundancy and response diversity of urban forests with previous land use, which may indicate a greater vulnerability of the functions provided by these forests. Thus, we emphasise in this study the importance of land use history for decision making in urban forest conservation policies and highlight the crucial role of natural remnant urban forests as reservoirs of functional diversity and stability in highly degraded and fragmented landscapes.