Demographic analysis of Agave angustifolia (Agavaceae) with an emphasis on ecological restoration

Abstract

We studied the demography of two populations of Agave angustifolia, one in a preserved tropical dry forest (Xochicalco), and the other one in a pastureland area used for cattle grazing (Tembembe), to test whether populations are likely to thrive on the deteriorated habitats left after cattle ranching. Seed germination and seedling survival experiments were carried out in different natural microsites (i.e. under tree canopies and in open microsites). We built Lefkovitch matrices and carried out prospective (elasticity) and retrospective (Life Table Response Experiments) analyses for both populations. Numerical simulations were performed to project the effect of inflorescences harvest and seedling introduction. Seedling survival and seed germination were highest in Tembembe. Population growth rate was slightly higher in Tembembe (lambda = 1.268) than in Xochicalco (lambda = 1.208). Prospective and retrospective analyses showed that stasis and growth contributed most to population growth rate and that the differences between the two populations were accounted for a lower fecundity and stasis in Xochicalco compared to Tembembe. Simulations of inflorescence harvest showed that lambda dropped below unity only when all inflorescences were eliminated. The simulated introduction of seedlings produced a substantial rise in lambda. As the lambda values reflect thriving populations at both sites, we suggest that this species could be successfully used in restoration programs.