Tree species diversity driven by environmental and anthropogenic factors in tropical dry forest fragments of central Veracruz, Mexico

Abstract

We examined vegetation structure and woody species diversity in relation to 14 environmental and anthropogenic factors in ten tropical dry forest (TDF) fragments in central Veracruz, Mexico. The basal area of the canopy (30.2 ± 2.11 m 2 /ha) and understory (1.96 ± 0.12 m 2 /ha) trees was similar, but density (1,014 ± 104 and 2,532 ± 227 individuals/ha, respectively) differed among sites. We recorded 98 canopy, 77 understory, and 60 seedling species. Richness was 24-45 species per site, Fisher's alpha and Shannon's indices increased with site altitude. Chao Jaccard indices revealed high species turnover, and a consistently higher similarity within the sites at the lowest and within the highest elevation sites. Ordination identified altitude, aspect, slope, water proximity, cattle and trails as significant explanatory variables of species patterns, and showed that sites at lower elevations were clearly separated from the other sites. Environmental heterogeneity alone did not control species diversity distribution, but species were affected by environmental filters at different stages in their life cycle, e.g., water proximity was significant for saplings and seedlings but not for adults. Anthropogenic disturbances act synergistically, e.g., trails played a key role in determining structure and tree diversity patterns. An important finding is that human disturbance diminishes species diversity in this TDF, but sites at lower elevations were more disturbed and less diverse, therefore we need to study how environmental factors would act if there were no anthropogenic disturbance.

Vegetative and reproductive tree phenology of ecological groups in a tropical dry forest in central Veracruz, Mexico

“…In several dry forests, it has been reported that anemochory is the most frequent dispersal mode with most seeds falling during the dry season (Griz & Machado 2001, Quesada et al 2009, 2014, and autochory is displayed by Fabaceae trees which is one of the most abundant families in our forest (Williams-Linera & Lorea 2009). An association between seed dispersal syndrome and fruiting phenology has been reported for several dry forests.…”

“…and Tabebuia chrysantha (Jacq.) G. Nicholson (Williams-Linera & Lorea 2009). The climate is warm sub-humid with summer rain (Aw o in Köppen's classification, Soto & García, 1989).…”

“…Tropical dry forest are heterogeneous communities with a mosaic of habitats where tree species with different successional status are suited to conditions such as seasonally closed canopy or canopy gaps (Williams-Linera & Lorea 2009, Hernández-Lezama 2016. Changes in vegetative and reproductive phenology as a function of successional status within a community have not received much study for dry forest.…”

Soil seed bank, seed removal, and germination in a seasonally dry tropical forest in Veracruz, Mexico

“…The soil was collected from fi ve fallow sites and two forest fragments in late May 2008, just before the onset of the rainy season that triggers seed germination (Table 1). At each study site, ten soil samples (30 cm × 30 cm and 5 cm depth) were collected on plots previously established for vegetation studies (Williams-Linera and Lorea, 2009;Williams-Linera et al, 2011). The soil samples were transported to a greenhouse located on the campus of the University of Veracruz in Xalapa.…”

Trees in the Agricultural Matrix: Reforestation Processes in a Tropical Dry Landscape in Chinandega, Nicaragua

“…However, there is reduced diversity in areas of severe anthropogenic disturbance, particularly involving cattle grazing, fire and wood extraction (Gillespie et al 2000, Willians-Linera andLorea 2009). Though no plant species has been verified as extinct in the Central American TDF, the level of fragmentation may not retain sufficient genetic diversity to safeguard continued success of populations, and a more disturbed forest will have reductions in productivity, financial value, and commercially-valuable species (Gillespie 2000, Williams-Linera andLorea 2009).…”