Aims We aimed to evaluate how climatic fluctuations influence the plasticity of anatomical vessel traits and the width of annual tree-rings of two relict-endemic Mexican Magnolia species. Notwithstanding, few studies have assessed the drought effect on vessel traits in tropical montane cloud trees of eastern Mexico. Methods Through digital images of growth rings, we assessed the tree radial growth rate, age of the trees and plasticity in vessel traits regarding climatic fluctuations of the Mexican Magnolia species studied. We compared vessel density, hydraulic diameter and percentage of conductive area in drought years (DY) and non-drought years (NDY) in two Mexican Magnolia species. Important Findings For the first time, the plasticity that occurs in porous wood vessel traits to long-term climatic fluctuations was analysed for two endangered Magnolia species (Magnolia vovidesii and M. schiedeana) from two tropical montane cloud forests in Mexico. We found that temperature and precipitation were strongly associated with differences in tree-ring width when DY and NDY were compared. Our analyses revealed that a high plasticity in vessel anatomy of diffuse-porous wood was related to temperature and/or water availability for both Magnolia species studied. We concluded that anatomical adaptations to DY resulted in a substantial reduction in vessel traits when compared with NDY, and that the plastic adaptations played an essential role in water transport and safety for the survival of the studied species during stressful long periods.

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Fagus grandifolia subsp. mexicana (Fagaceae) is a taxon endemic to Mexico and is currently considered to be in danger of extinction. It dominates the canopy at the sites where it grows, forming the plant association known as Mexican beech forest. The objectives of this study were to (1) determine the area currently occupied by beech forests in Mexico, based on a literature review; (2) generate maps showing the distribution and area occupied by the less known beech forests in Mexico (which are located in the state of Hidalgo) based on field observations and using geographic information systems; and (3) propose measures that can be taken to protect and manage this plant association. The results show that the beech forests of Mexico currently cover an area of 155.54 ha, and several fragments have recently disappeared. The largest patches of beech forest are located at 5 sites in the state of Hidalgo and occupy a total area of 106.79 ha (73.9%). Each of the sites is different in size, connectedness, and degree of fragmentation and disturbance. The Mexican beech forests urgently require management and conservation programs, as some of them will otherwise soon disappear due to changes in land use, logging, and climate change. To preserve these forests the following measures are suggested in the short term: increase connectedness between beech forest patches, create core areas, reforest with native species, create seed concentrations, regulate the consumption of beechnuts by humans, and include this plant association in the National System of Natural Protected Areas.

The Mexican tropical montane cloud forest trees occur under special and limited climatic conditions; many of these species are particularly more sensitive to drought stress. Hydric transport in leaf veins and wood features are influenced by climatic variations and individual intrinsic factors, which are essential processes influencing xylogenesis. We assessed the plastic response to climatic oscillation in two relict-endangered Magnolia schiedeana Schltdl. populations and associated the architecture of leaf vein traits with microenvironmental factors and wood anatomy features with climatic variables. The microenvironmental factors differed significantly between the two Magnolia populations and significantly influenced variation in M. schiedeana leaf venation traits. The independent chronologies developed for the two study forests were dated back 171–190 years. The climate-growth analysis showed that M. schiedeana growth is strongly related to summer conditions and growth responses to Tmax, Tmin, and precipitation. Our study highlights the use of dendroecological tools to detect drought effects. This association also describes modifications in vessel traits recorded before, during, and after drought events. In conclusion, our results advance our understanding of the leaf vein traits and wood anatomy plasticity in response to microenvironmental fluctuations and climate in the tropical montane cloud forest.

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