중남미

The mountain juniper Juniperus monticola Martinez, a decumbent alpine shrub found at elevations up to 4600 m a.s.l. on the high mountains of central Mexico, is the woody species growing at highest elevation in North America. It reaches an age close to a millenium, which probably makes it the oldest alpine shrub in the world. We conducted a dendrochronological study of this species at Pico de Orizaba volcano, the highest peak in Mexico, to analyze its dendroclimatic potential and the influence of ocean-atmospheric forcing on the interannual variability of radial growth. A ring-width chronology was developed extending from 1178 to 2016 (839 years). Climate data from a local weather station and from CRU TS version 4.01 were used to determine the climatic response of J. monticola. The species is positively correlated to the average maximum temperature of May–June (r = 0.38, p < 0.05) and negatively to the March-April precipitation (r = −0.44, p < 0.05) of the local weather station. Gridded drought indices (PDSI, SPEI) were used to analyze the combined effect of rising temperatures and evapotranspiration on ring-width. A significant negative response (r = −0.354, p < 0.01) was found between the instrumental PDSI records (June, July, August) and the ring-width series; similarly, a negative correlation was obtained for the SPEI from December of the previous year to June of the current year (r = −0.4, p < 0.01). These negative correlations suggest that higher temperatures occurring in recent decades are favoring increases in radial growth. The ring-width chronology is significantly correlated, although weakly, with the El Niño/Southern Oscillation, the Pacific Decadal Oscillation, and the Atlantic Multi-decadal Oscillation, consistent with the influence of those phenomena on PDSI and SPEI over central Mexico.