Drought is a major constraint of forest productivity and tree growth across diverse habitat types. In this study, we investigated the drought responses of four conifer species growing within two locations of differing elevation and climatic conditions in northern Mexico. Two species were selected at a mesic site (Cupressus lusitanica Mill., Abies durangensis Martínez) and the other two species were sampled at a xeric site (Pinus engelmannii Carr., Pinus cembroides Zucc.). Using a dendrochronological approach, we correlated the radial-growth series of each species and the climatic variables. All study species positively responded to wet-cool conditions during winter and spring. Despite the close proximity of species at a mesic site, A. durangensis had high responsiveness to hydroclimatic variability, but C. lusitanica was not responsive. At the xeric site, P. engelmannii and P. cembroides were very responsive to drought severity, differentiated only by the longer time scale of the response to accumulated drought of P. engelmannii. The responsiveness to hydroclimate and drought of these tree species seems to be modulated by site conditions, or by the functional features of each species that are still little explored. These findings indicate that differentiating between mesic and xeric habitats is a too coarse approach in diverse forests with a high topographic heterogeneity.

Abstract:The existence of endangered tree species in Mexico necessitates an understanding of their vulnerability to the predicted climate changes (warming and drying trends). In this study, the sensitivity to climate of earlywood (EW) and latewood (LW) widths of the threatened Picea chihuahuana was determined. The response of EW and LW to climate variables (maximum temperature, minimum temperature, precipitation, evaporation, and a drought index) was analyzed by means of correlation analysis using dendrochronology over the period of 1950-2015. EW and LW production were enhanced by cool and wet conditions during winter prior to the start of growing season. During the growing season, EW and LW production increased in response to cool spring and summer conditions, respectively; temperatures and year-round evaporation, excluding summer and the previous drought in the period prior to the growing season. EW was sensitive to seasonal drought, which is a concern considering the predicted aridification trends for the study area. These results provide further knowledge on the dendroecological potential of Picea chihuahuana.

Dendrochronology is a very useful science to reconstruct the long-term responses of trees and other woody plants forming annual rings in response to their environment. The present review considered Mexico, a megadiverse country with a high potential for tree-ring sciences given its high climatic and environmental variability. We reviewed papers considering Mexican tree species that were published from 2001 to 2016. Most of these studies examined tree species from temperate forests, mainly in the pine and fir species. The review included 31 tree species. The most intensively sampled family and species were the Pinaceae and Douglas fir (Pseudotsuga menziessi (Mirb.) Franco), respectively. Some threatened tree species were also studied. Dendrochronological investigations were mainly conducted in northern and central Mexico, with Durango being the most sampled state. The reviewed studies were mostly developed for hydroclimatic reconstructions, which were mainly based on the tree-ring width as a proxy for the climate. Tree-ring studies were carried out in both national and foreign institutions. Our review identified relevant research gaps for dendrochronologists such as: (i) biomes which are still scarcely studied (e.g., tropical dry forests) and (ii) approaches still rarely applied to Mexican forests as dendroecology.

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Warming-amplified drought stress may decrease productivity and growth in both wet and dry conifer forest ecosystems. However, the seasonal radial-growth responses to climate, drought and related climate atmospheric patterns have not been compared in detail in wet and dry sites. We focus on drought-prone northern Mexico conifer forests and compare growth responses in tree species from wet (Pseudotsuga menziesii) and dry sites (Pinus leiophylla). to characterize the responsiveness to interand intra-annual changes in water availability we used dendrochronology and measured tree-ring (TRW), earlywood (EW) and latewood (LW) widths. We calculated adjusted LW (LWadj) by removing the influence of EW on LW. We identified E(narrow tracheids within the earlywood) and L-type (wide tracheids within the latewood) intra-annual density fluctuations (IADFs) and related their frequencies to seasonal climate and drought. We also related growth to atmospheric patterns related to the El NiñoSouthern Oscillation (ENSO) which drives precipitation patterns in the studied region. Wet-cool conditions during the prior winter and current spring linked to El Niño events enhanced TRW and EW, particularly in P. menziesii, whereas wet summer conditions enhanced LWadj. The formation of E(P. leiophylla) and L-type (P. menziesii) IADFs was associated with seasonal fluctuations in precipitation and temperature, suggesting different strategies to withstand drought. the sensitive P. menziesii strongly responded to short spring droughts, whereas the tolerant P. leiophylla responded to longer spring droughts. Seasonal wood measures (EW, LWadj) and IADFs are proxies of intra-annual fluctuations in water availability in similar conifer forests.

Los anillos de crecimiento de los árboles han sido útiles como indicadores para estimar la captura de carbono en los ecosistemas forestales. México es considerado un país megadiverso con un gran potencial para las dendrociencias dada su alta variabilidad ambiental. El objetivo del presente estudio es presentar la perspectiva que ofrecen los anillos de crecimiento de los árboles para estimar la captura potencial de carbono en México. Se realizó una revisión bibliográfica a escala mundial, considerando estudios que abarcan proxies dendroecológicos sobre el contenido de carbono almacenado. La revisión incluyó 74 estudios publicados entre 2004 y 2019. Las investigaciones dendroecológicas del contenido de carbono se realizaron principalmente a partir de 2012 en México. La mayoría de estos estudios se basaron en especies como Pinus sylvestris y Fagus sylvatica. Adoptando un enfoque dendroecológico, asociado con técnicas alométricas este estudio ofrece una gran oportunidad para promover el desarrollo del estudio de la dinámica del carbono almacenado en México.

Research Highlights: Analyzing the contrasting ecological gradients makes it easier to understand the influence of climate on carbon accumulation. Background and Objectives: The increasing climatic variability has implications for vegetation, impacting on its ecological functions, among which carbon accumulation stands out. In the present study, we used climate-dendrochronology relationships to evaluate carbon accumulation in two conifer species that grow in contrasting humidity sites: Pinus strobiformis Engelm (mesic sites) and Pinus leiophylla var. chihuahuana (Engelm.) Shaw (arid sites). Materials and Methods: Using a dendrochronological approach, we estimated the correlation of biomass and carbon accumulation of each species with some climatic variables (temperature, precipitation, and a drought index) and generated a linear mixed model. Results: The response in carbon accumulation between species with respect to climate was significantly different. P. strobiformis showed a positive correlation with the climatic variables analyzed, while in P. leiophylla the correlation was negative, except with precipitation. Conclusions: These results show that forests in both mesic and arid sites are prone to climate changes, although their responses are different, impacting the productivity and carbon cycles of forest ecosystems.