Tree rings as indicators of climatic variation in the Trans-Mexican Volcanic Belt, central Mexico

Abstract

How tree growth responds to climate is determined by temperature and water availability, but climate change is causing shifts in forest growth that could be evaluated through tree-ring growth studies given that it is annual radial increase is influenced by interannual and multiannual climatic variations. We evaluated the influence of oceanic-atmospheric indices and the climate response on the annual radial increase of Pinus hartwegii Lindl. A total of 140 increment cores were obtained from 82 selected P. hartwegii specimens growing at the treeline of the Tancítaro stratovolcano, Michoacán, Mexico to develop a 348-year long ring-width chronology. Correlation and response function analyses were carried out between the tree-ring series and monthly climate records and by subperiods of 50 yrs. Climate records were obtained from six weather stations near the study site and oceanic-atmospheric indices were downloaded from international climatic sources. The chronology was related to drought indices involving precipitation, temperature, evaporation, and soil water content. The results indicated that accumulated precipitation from February to April, and the mean and minimum temperature from March to May and from September to November of the current growth year, had a positive correlation with the P. hartwegii ring-width chronology. The maximum temperature of March and May of the current growth year produced a negative correlation and in November positive correlation. The analysis of the response function indicated that P. hartwegii had a negative growth response to the average and maximum temperature of March. The analysis of the response function in 50-year subperiods indicated a stable response in precipitation from February to April of the period 1925 to 2000. However, when the temperature increased, the stability of the growth response became negative, mainly due to an increase in temperature in combination with low precipitation volumes, which usually occurs from March to May. The association between the ring-width series, and indices of ENSO (MEI, El Niño 4) showed a significant positive correlation, but negative with SOI. Similarly, the relationship with the PDO was positive, but negative with AMO. The association with drought indices (PDSI + JJA, PDSI*, SPEI) was positive and significant. We conclude that the populations of P. hartwegii of the Tancítaro stratovolcano constitute an ecological indicator of long-term precipitation and temperature variability and is a high-resolution proxy for regional rainfall reconstruction at least for the last three centuries.