INFLUENCIA CLIMÁTICA EN EL RECLUTAMIENTO DE Pinus hartwegii Lindl. DEL ECOTONO BOSQUE-PASTIZAL ALPINO EN MONTE TLÁLOC, MÉXICO.

The upper timberline in Mexico is expected to be sensitive to climate change. Therefore, Pinus hartwegii recruitment at Monte Tlaloc's tree line ecotone, in the Estado de Mexico, was analyzed, in order to detect a possible progress in the altitude interval of the species, as a result of higher temperatures. To explore the influence of climate in the recruitment pattern, we compared the age frequency of P. hartwegii with temperature and rainfall; additionally, we analyzed this impact on the basis of the year to year change in the thickness of their growth rings and its relationship with the El Niño-Southern Oscillation (ENSO). The age frequency was based on a 269 trees simple; their growth rings were dated a year after they were formed. P. hartwegii recruitment has increased since the late 1970s, which matches the rise in temperature, especially during El Niño events. This situation was made evident by a lower radial increase than the mean of trees found below the upper timberline. The wet periods detected in the years before the greater recruitment years could imply that optimal temperature conditions at greater altitude are not enough to promote a progress in the wider distribution of the species, but that the wetness level must be enough to optimize its development. The lack of synchrony between the recruitment and the radial growth of trees established at lower altitudes suggests an opposite climate impact in the species' growth, which implies a possible long-term withdrawal of the altitude extent. [ABSTRACT FROM AUTHOR]