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We evaluated the regeneration behavior and early growth rates of 10 non-pioneer canopy tree species in medium-height, semi-evergreen dry tropical forest in Quintana Roo, Mexico. These species provide timber and non-timber forest products for local communities and include evergreen and deciduous species with varied dispersal mechanisms. The species were Coccoloba spicata, Cordia dodecandra, Dendropanax arboreus, Guettarda combsii, Lysiloma latisiliquum, Manilkara zapota, Metopium brownei, Piscidia piscipula, Platymiscium yucatanum, and Sabal yapa.
An evaluation of seedling abundances in understory and open conditions, understory seedling spatial aggregation, and adult size frequency distributions revealed divergent regeneration behaviors. Among the 10 species, we detected three processes limiting regeneration: seed availability, resource conditions, and negative density dependence. Based on observed regeneration behaviors, species were assigned to five regeneration behavior groups, reflecting, in part, inferred shade tolerance. Highly shade intolerant species would have been favored by past slash and burn agriculture.
We evaluated growth responses of individuals regenerating in 0.5 ha artificial clearings to a number of biotic and abiotic factors using neighborhood measures and model selection based on Akaike’s Information Criterion (AIC). Neighbors reduced both height and diameter growth rates for most, but not all, target species within 4-5 years of opening creation. Species responses to soil factors were highly individualistic. For some species, competitive response depended on edaphic factors. Individualistic responses of species to these biotic and abiotic factors suggest that diversity may be maintained, in part, by very early niche partitioning. Neither inherent growth rate nor competitive response alone corresponded with species groupings derived from shade tolerance characteristics. However, shade tolerance was associated with an early size hierarchy among the species and with their final crown class positions.
The silvicultural implications of our research results, other studies in Quintana Roo, and the historic disturbance regime are discussed. Slash and burn agriculture is identified as a central and more important component of the historic disturbance regime than hurricanes. Based on the wide range of observed regeneration behaviors, recommended silviculture techniques to maintain current species composition include variably-sized patch cuts, site preparation, control of competing vegetation, and seed tree and structural retention. |
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