Gap-building-phase regeneration in a tropical montane cloud forest of north-eastern Mexico

Regeneration processes associated with gap-building-phase sites are described for the tropical montane cloud forest of the El Cielo Biosphere Reserve in Tamaulipas, Mexico. Twelve gap-building-phase sites c. 20 y old were selected within the forest according to their gap size and severity of disturbance (i.e. number of fallen logs). All flowering plants were recorded within the sites and specimens were identified to species level. Species were related to genera geographical affinity and growth form. Abundance, individual height and aerial crown cover were also recorded for all species. The composition for these sites was 121 vascular plant species grouped in 96 genera and 60 families. Results suggest that the advanced regeneration of shrub and tree species of the medium canopy, such as Eugenia capuli, Ternstroemia sylvatica, Turpinia occidentalis, Meliosma oaxacana, Myrsine coriacea and Podocarpus reichei, was favoured by the disturbance regime prevailing in this forest community. All of these woody species belong to tropical genera and are structurally dominant in the gap-building-phase sites. A differential response of the vegetation was obtained in these sites as a function of the severity of disturbance and gap size. This response was revealed by the dominance-diversity relationships. Small gaps (45–95 m2) or gaps created by two treefalls showed a higher diversity and density compared to larger gaps (95–150 m2) or those created by four fallen logs, which had a lower species diversity and significantly lower tree and vine densities. These results imply that gap size and the severity of disturbance have a significant effect on the regeneration of these disturbed sites.