Dinámica y conservación de la flora del matorral xerófilo de la Reserva Ecológica del Pedregal de San Ángel (D.F., México)

The xerophytic scrub located on the lava field produced by the Xitle volcano has been almost completely destroyed by the urban sprawl of Mexico City. The Pedregal de San Angel Ecological reserve (1.77 km2) offers protection to one of the most important remnant portions. Despite such protection status, this plant community is presently still affected by invasion of exotic species, pollution, illegal extraction of selected species, and recurrent fires. The aim of this study was to update the floristic knowledge of the reserve and to analyze possible changes in the floristic richness and composition that have taken place in the last 50 years. Out of the total 337 species that are included in the present checklist (193 genera, 74 families), 152 species had already been reported by Rzedowski (1954) in a pioneer study that covered the entire lava field (80 km2). Contrastingly, 166 species recorded by him for this xerophytic scrub were not encountered in this study, although 21 of them do occur in another ecological reserve (Lomas del Seminario) located on the same lava field but at a higher elevation. The analysis of the distribution of species of the present checklist by vegetation type showed that only 34 of them occur exclusively in xerophytic scrub, whereas the remaining also occur in other plant communities. The information provided in this study is expected to serve as the basis for future monitoring studies aimed at assessing the dynamics of this flora through time.