As the design of tree bases along streets in cities makes them potential ecological corridors, urban tree bases may be a key contributor to the overall connectivity of the urban ecosystem. However, they are also a highly fragmented environment in which extinctions are frequent. The goal of this study was to assess the plant species ability to survive and spread through urban tree bases. To do so, we developed a Bayesian framework to assess the extinction risk of a plant metapopulation using presence/absence data, assuming that the occupancy dynamics was described by a Hidden Markov Model. The novelty of our approach is to take into account the combined effect of low-distance dispersal and the potential presence of a seed bank on the extinction risk. We introduced a metric of the extinction risk and examined its performance over a wide range of metapopulation parameters. We applied our framework to yearly floristic inventories carried out in 1324 tree bases in Paris, France. While local extinction risks were generally high, the extinction risk at the street scale varied greatly from one species to another. We identified 10 plant species that could survive and spread through urban tree bases, and three biological traits correlated with the extinction risk at the metapopulation scale: the maximal height, and the beginning and end of the flowering period. Our results suggest that some plant species can use urban tree bases as ecological corridors despite high local extinction risks. We also identified several biological traits correlated with the ability to survive in tree bases, some of them being not previously known. Moreover, our findings demonstrate that the approach we introduced to assess the extinction risk has the potential to be extended to more general metapopulations.