Small-Scale Environmental Drivers of Plant Community Structure and Diversity in Neotropical Montane Cloud Forests Harboring Threatened Magnolia dealbata in Southern Mexico

Reyna Domínguez-Yescas,Eduardo Salcedo-Pérez,Miguel Ángel Muñiz-Castro,José Antonio Vázquez-García,Gerardo Hernández-Vera,Ciro Rodríguez-Pérez,Sergio Ignacio Gallardo-Yobal

doi:10.3390/d12120444

Abstract

Gradient analysis was used to determine factors driving small-scale variation of cloud forest communities harboring Magnolia dealbata, a threatened species and bioculturally relevant tree for the Chinantecan, Mazatecan, Nahuan, and Zapotecan ethnicities in southern Mexico. Particularly, we aimed to: (a) determine factors explaining major community gradients at different heterogeneity scales along a small-scale elevational gradient, (b) test the Decreasing and the Continuum hypotheses along elevation, and (c) classify vegetation to assist in identifying conservation priorities. We used a stratified random sampling scheme for 21 woody stands along a small-scale (352 m) elevational transect. Four main data matrices were used (presence-absence, density, basal area, and guild data). Through Non-metric Multidimensional Scaling (NMS), Principal Coordinates Analysis (PCoA), and distance-based Redundancy Analysis (db-RDA), we found that major community variation was explained by soil pH, displaying an outstanding vegetation discontinuity, separating the species-rich relic Oreomunnea-Ticodendron-stands from stands with higher importance values for M. dealbata. The high species richness observed was explained by a combination of the windward effect of dry-seasonal maximum cloud condensation gain and habitat differentiation-specialization, a phenomenon that may also explain the mid-peak hypothesis and ensure the survival of relic species. Sampling-truncation and conservation status also played a role in this. Our results do not support the Decreasing and Continuum hypotheses along elevation.

Highlights

Neotropical montane cloud forests (CF) are known to display high gamma, beta, and alpha species diversity, environmental heterogeneity, endemism, and a high number of species of conservation concern
Spatial environmental variation in temperature, light, soil pH, moisture, nitrogen, and altitude at any scale may drive to the occurrence of habitat-specialized plant species [104,105], which leads to changes in species composition even on small scales
Major small-scale CF community variation was explained by soil pH, while elevation, K, Na, and firewood extraction were environmental variables of secondary importance

Summary

Introduction

Neotropical montane cloud forests (CF) are known to display high gamma, beta, and alpha species diversity, environmental heterogeneity, endemism, and a high number of species of conservation concern They form a continental pattern of island-like fragmented habitats resembling archipelagos [1,2,3,4,5,6,7,8]. In Southern Mexico, in the state of Oaxaca, CF occurs in six physiographic provinces [12] in close interaction with a complex and long biocultural gradient of high ethnic and language turnover, including Chinantecos, Cuicatlecos, Mazatecos, Mixtecos, Nahuas, Triquis, Zapotecos, and Zoques [13] Gradient analyses of these forests have focused on La Chinantla [14], Tiltepec [15], Huautla de Jiménez [16], Sierra de Juárez [17], Sierra Mazateca [18], and Santa Cruz. Only those from the Sierra de Juárez de Oaxaca (Ixtlán de Juárez, Villa Alta) and Sierra Mazateca are confirmed to harbor the narrowly endemic, bioculturally relevant and threatened CF tree Magnolia dealbata Zucc. [20,21,22]

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Discussion

Conclusion