Precipitation trends in areas sustaining populations of Swietenia macrophylla (Meliaceae): Implications for the future natural regeneration of an economically valuable tropical tree in Mexico

Background: Climate change could have differential impacts on economically valuable tropical trees. Identification of statistical trends improves knowledge about how changes in rainfall are occurring in space and time. Questions: Are distinct areas supporting S. macrophylla populations exposed to different patterns of rainfall that could differentially affect their future natural regeneration? Studied species: Swietenia macrophylla King (Meliaceae) Study site and dates: Southern Mexico during the period 1980-2011. Methods: Databases from monthly precipitation and annual standardized precipitation index (SPI, used to detect hydrological droughts) were obtained and homogenized from 90 weather stations located throughout the distribution area of S. macrophylla. Mann-Kendall analyses (S) were performed on time series of both variables from the 1980–2011 period to statistically identify trends of change. Statistical significance of S was obtained using an approximation to the normal distribution (standardized Z value). Trends were interpreted at two levels, per weather station and per state. Results: Fifty eighth of the 90 stations (64.4 %) showed climatic changes either for precipitation or SPI. Regarding the magnitude of Z, the number of stations (47) with negative trends for both variables doubled the number of stations (25) with positive trends. Reductions in precipitation and SPI indicate an overall trend toward drier climates in the most commercially important areas. Conversely, favorable conditions were found in Chiapas, Mexico. Conclusions: Areas with higher commercial value experienced reductions in precipitation and increases in hydrological droughts. If these trends continue, the natural regeneration of S. macrophylla could be negatively impacted in the future.