Structural heterogeneity of mangroves as a response of environmental and anthropic factors in Soconusco, Chiapas, Mexico

Structural characteristics and dominance patterns in mangroves have been linked to environmental, anthropogenic and ecophysiological factors. The Soconusco on the southern coast of the Mexican Pacific is an environmentally heterogeneous region, with high availability of freshwater and different degrees of E. I. Romero-Berny, C. Tovilla-Hernández, N. Torrescano-Valle, y B. Schmook HETEROGENEIDAD ESTRUCTURAL DEL MANGLAR COMO RESPUESTA A FACTORES AMBIENTALES Y ANTRÓPICOS EN EL SOCONUSCO, CHIAPAS, MÉXICO. STRUCTURAL HETEROGENEITY OF MANGROVES AS A RESPONSE OF ENVIRONMENTAL AND ANTHROPIC FACTORS IN SOCONUSCO, CHIAPAS, MEXICO. Instituto Politécnico Nacional Núm. 47: 39-58. Enero 2019 DOI: 10.18387/polibotanica.47.4 Núm. 47: 39-58 Enero 2019 ISSN electrónico: 2395-9525 41 impact. The goal of this study was to analyze the mangrove groups, including their structure and dominance pattern under the influence of eight environmental factors (salinity, flood level, pH, air temperature, soil temperature, relative humidity, and content of organic matter 0-30 cm, 0-60 cm). The characteristic physical features and caused by the impact were described for each group. Mangrove structure was evaluated considering a forest inventory conducted in 40 sampling units (300 m). Density of live and standing dead trees, stumps and seedlings was estimated for 1ha. The dominance for each species was determined using the relative Importance Value. The identification of groups was carried out with ordination and classification routines. The species with the highest Importance Values were Rhizophora mangle (29.68%) and Laguncularia racemosa (27.33%). Comparatively, the general structure of mangroves in Soconusco in terms of density (2 792 steams ha), basal area (36.5 mha) and height (15.5 m) is greater than in other areas of the Mexican Pacific coast. Classification of vegetation data, based on the Relative Importance Value Index, defined five mangrove groups. Outstanding is the presence of a community dominated by Pachira aquatica. The highest density of trees and stumps was recorded in Conocarpus erectus grouping, while the highest density of seedlings was in Avicennia germinans grouping. 86.3% of sampled trees present ≤ 17.7cm diameter at breast height. The variables that correlate significantly with the axis 2 of the ordination biplot were organic matter (30-60 cm), salinity and flood level. Canonical Discriminant Analysis corroborated the differences between mangrove groups, with the first two canonical axes explaining 89.05% of the variation in the data. The community composition varied associated with physical and environmental conditions, and were structurally defined by basal area, crown diameter, height and density, as well as by factors that can be associated with an anthropic impact such as stump and seedling densities. It is recommended to consider the characteristics of each mangrove group to plan their management.