First oxygen and carbon stable isotope chronologies from high-elevation tropical forests in South America

MILAGROS RODRIGUEZ CATÓN; LAIA ANDREU-HAYLES; MARIANO SANTOS MORALES; CHRISTIE, D; RAO, MUKUND; DAUX, VALÉRIE; RICARDO VILLALBA

Seminario; Biology and Paleo Envirnonment weekly seminar; 2019

Polylepis tarapacana (queñoa) is the highest-elevation tree species in the world, growing at altitudes between 4200 and 5100 m a.s.l. along the South American Altiplano. This species can live longer than 700 years under extremely harsh environments, with less than 300 mm of annual precipitation and wide daily thermal amplitudes, from below 0° to over 20°C all year round. So far the literature has mostly reported that variations in water availability are the main driver of stem growth for this tropical treeline species, but the role of temperature in modulating its radial growth is still unclear. For this study we generated ring-width, oxygen (δ18O) and carbon (δ13C) stable isotopic tree-ring chronologies at four P. tarapacana sites located along an aridity gradient from 18 to 22ºS, in order to (1) assess the climate responses of both stem growth and stable isotopes of P. tarapacana, and (2) explore the potential of stable isotopes for climate reconstruction in the high-elevation tropics. Results suggest that the limiting factor for growth vary along the aridity gradient from north to south. While temperature seems to enhance radial growth in the northern and wetter sites, precipitation conditions long before the start of the growing season are modulating growth in the southern and drier sites. On the other hand during the growing season higher temperatures and lower precipitations are related to an enrichment of both δ18O and δ13C. Additionally, oxygen stable isotopes show a great potential for annual-resolution reconstruction of precipitation and temperature variability in the high-altitude tropics in South America. In the context of global warming and the precipitation decrease observed over the last 70 years in the Altiplano, one of the driest regions in the world, these results are important for assessing the vulnerability of high elevation Polylepis forests to climate change as well as providing high-resolution palaeoclimatic proxies.