Climate impacts on tree growth in a Neotropical high mountain forest of the Peruvian Andes

Abstract

Global warming can jeopardize important ecosystem functions and services in sensitive Neotropical mountain areas. However, untangling the relative roles of natural climate variability pattern from current global warming trends still represent a major challenge. Here, we propose a novel analytical approach based on Structural Equation Models to evaluate the relative roles of different sources of climate variability on tree growth. Specifically, we investigate direct and indirect linkages between Basal Area Increments (BAI) and a set of different climatic sources of variability, such as: (i) large-scale atmospheric oscillation patterns (i.e., the El Niño Southern Oscillation, ENSO and the Pacific Decadal Oscillation, PDO); and (ii) local meteorology in terms of temperature and precipitation. Additionally, we included in the SEM framework other important variables such as: (iii) calendar year (representative of temporal linear trends); and (iv) tree size (representative of main biological trends). Results indicate that the ENSO and PDO modulate minimum temperatures (Tmin) in the study area. These indices describe the oscillating behavior of the climatic modes (i.e., South Oscillation Index and PDO index) and are negatively correlated with Tmin. As such, they also influence tree growth (represented here by BAI) indirectly. Furthermore, through its direct impact on Tmin increase, ongoing climate warming has an indirect negative effect on BAI, thereby implying that the ongoing temperature rise could exert control on productivity in high mountain forests of the Andes, and that this influence could become more important with continued temperature increase.