High Elevation Monitoring in the North American Tropics: Ecosystem/Climate Relationships on Nevado de Colima, Mexico

High elevation monitoring in the tropics is uncommon. Presented here are the 2001-2004 results of an intensive field study from Nevado de Colima, Mexico. The site is at 3800 m at 19° 34' N, a few hundred meters below tree line. We have been co-monitoring weather and tree growth at half-hour intervals, as well as seasonally averaged stable isotopes throughout the hydrologic/biologic cycle. The site is under the influence of the North American monsoon, which determines a wet-summer, dry-winter climatic regime. Using point and band dendrometers, we have shown the response of high elevation Pinus hartwegii trees to changing weather patterns and attempted to pinpoint factors related to onset and cessation of growth in these high elevation tropical trees. Precipitation, temperature and relative humidity are shown to influence stem size at a range of timescales. Along with the stable isotope data collected to date, we hope to build a model of tree growth and stable isotope incorporation into tree-ring cellulose. This will allow a calibrated chemical reconstruction of seasonal growth response to fluctuations in the monsoon over the length of the tree ring record (>350yr). We also had the unfortunate experience of monitoring several of our instrumented trees during a round-headed pine beetle (Dendroctonus adjunctus) infestation following an exceptionally dry winter the year before. These data may provide additional insight into tree response to drought stress and physiological response to bark beetle attacks.