Comparative demographic analysis in contrasting environments of Magnolia dealbata: an endangered species from Mexico

The study of population regulation and demography in natural habitats is critical for the conservation of rare and endangered species. We address the impact of cattle exclusion on the demographics of Magnolia dealbata (Magnoliaceae), an endangered species according to IUCN and Federal Mexican laws. Sixteen permanent plots were established, eight of which were enclosed to livestock, in the mountain cloud forest in Coyopolan, Mexico, which has the largest population of M. deadlbata. Censuses of the plots were undertaken annually during three annual cycles to record seed number, recruitment, mortality, and growth (defined as length and diameter at breast height). The effects of two treatments (with and without livestock exclusion) on the dynamics of M. dealbata were investigated using transition matrix models and life table response experiment (LTRE) analysis. Contrary to expectations, there was no significant effect of cattle exclusion on population growth rates (λ). Furthermore, the λ, estimated from the mean transition matrix for both treatments was greater than one. The transitions with the highest elasticity values were similar between the two treatments, while reproductive stage contributed more to differences in population growth rate and were less variable than the non-reproductive stage. LTRE analysis showed that treatment differences had little effect on λ. Livestock exclusion appears to lead more to differences in the arrangement of the values of the transition matrix than to the rate of population growth for M. dealbata.