Abstract
Aim of study: To determine the response of high-altitudinal forests to seasonal drought.Area of study: Monte Tláloc, Estado de México and Rancho Joyas del Durazno, Municipality of Río Verde, San Luis Potosí, México.Materials and methods: In this study, we evaluate the response to drought and hydroclimate in two young Mexican conifers sampled at high elevation, correlating records of tree-ring growth and the Normalized Difference Vegetation Index (NDVI).Main results: The results show that Pinus teocote and Abies religiosa are vulnerable to the precipitation regime and warm conditions of winter-spring. The physiological response mechanisms seem to be differentiated between the species, according to the effects of drought stress. The NDVI demonstrated the different temporal responses of the species according to their inherent physiological mechanisms in response to hydroclimatic limitations. This differentiation can be attributed to the spatial variation present in the particular physical and geographic conditions of each area. The dry and warm seasonal climates reveal P. teocote and A. religiosa to be species that are vulnerable to drought conditions. However, further evaluation of the resistance and resilience of these species is necessary, as well as disentanglement of the effects of associated mechanisms that can influence the predicted processes of extinction or migration.Research highlights: Pinus teocote and Abies religiosa are vulnerable to the seasonal drought conditions. These results are of particular importance given the climatic scenarios predicted for elevated ecotones. Tree-ring widths and NDVI improved the response of radial growth to the climate, enhancing our understanding of forest growth dynamics. The response to climatic variability depends on the particular species.Keywords: High elevation; tree-ring; ENSO; NDVI; climate-growth relationship. Abbreviations used: Normalized Difference Vegetation Index (NDVI); Tree-Ring Width (TRw); precipitation (PP); maximum temperature (Tmax); minimum temperature (Tmin); El Niño-Southern Oscillation (ENSO); Climatic Research Unit Time-series data version 4.04 data (CRU TS v. 4.04); Standardized Precipitation-Evapotranspiration Index (SPEI); Climatic Research Unit Time-series data version 4.03 data (CRU TS v. 4.03); first-order autocorrelation (AC); mean sensitivity (MS); mean correlation between trees (Rbt); expressed population signal (EPS); Ring Width Index (RWI).
Highlights
Materials and methodsThe conifers of Mexico are present across almost their entire biogeographic range (Farjon & Styles, 1997)
With respect to the El Niño-Southern Oscillation (ENSO) data, we found a positive association with growth during the period June to September in the year of tree-ring formation, albeit not significant
Wet and cool winter and spring conditions enhance radial growth; we did not find a positive response to the ENSO
Summary
The conifers of Mexico are present across almost their entire biogeographic range (Farjon & Styles, 1997). Previous studies that focused on old trees have reported high sensibility to climate vulnerability (Villanueva-Díaz et al, 2015), there is a lack of contribution in terms of young stands at high elevations These species play an important role in terms of providing goods and forest environmental services to the nearby population, as well as constituting a crucial reserve for wildlife (Rzedowski, 2006). We conducted the first comparison of radial growth sensitivity to drought in two conifer species that form pure and young stands in high-altitudinal ecotones. We sampled trees in two sites at the maximum range of their elevational distribution where these species are dominant on the studied mountain (Fig. 1, Table S1 [suppl.]) Both sites correspond to unevenly aged forest, currently under forest management, that forms young stands. The data were extracted from the SPEI webpage (https://spei.csic.es/) at a resolution of 0.5° from the database CRU TS v. 4.03 with a scale of 1 to 48 months from January to December of the years of growth for both species
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