Ecological status of Beaucarnea gracilis, an endemic species of the semiarid Tehuacan Valley, Mexico

We present a demographic analysis and suggestions for the conservations of Beaucarnea gracilis, a species endemic to the Tebuacan Valley, Puebla, Mexico. The species is dioecious, it flowers every year, and the breeding system and floral display are typical of a generalist mode of pollination. The density of B. gracilis in the study plot was 16.7 individuals/ha. Distribution of trunk diameter size classes fits a normal distribution (n = 404), but the smaller sizes were not found (<0.7 m). The inflorescences were visited by 46 insect species. Over 2600 seeds are produced per inflorescence; 27-30% are damaged by parasites, and the rest germinate readily (90-100%). Survival of seeds and seedling is very low. We found 313 seedlings in a 12-ha area, all (94.24%) of which were at the base of nurse plants; particularly Mimosa luisiana and Castela tortuosa. The ecological status of the population of Beaucarnea gracilis is relatively good for adult individuals. In addition to low recruitment, (whether natural or human influenced), past extraction of seedlings for commerce, grazing by goats, and land clearing for corn cultivation, highway construction, and urbanization, are a real threat to the survival and establishment of seeds and seedlings. Conservation of this slow-growing, long-lived species should be promoted because (1) ecologically, it is a feeding center for many insect species, an important host for many Bromeliaceae, and part of the highly rich and endemic flora of Tebuacan and (2) economically, it helps low income people in the area (seedlings raised for commerce). Protection of nurse plants, regulation of grazing by goats, a halt to illegal extraction, and conservation of areas of the Tebuacan valley will help the survival of this species in nature.