Climate Change

Biography

Biography: Carlos A Gracia

Abstract

Trees in the tropical and subtropical mountains of South America are able to develop at high elevation, with some species forming the highest tree-line in the world at 5200m. Under these unique environmental conditions, only evergreen trees of the genus Polylepis are able to subsist. Polylepis reticulata is a very slow growth tree. The strategy of these trees to survive in such unfavorable conditions has been analyzed in the Cajas National Park (Azuay, Ecuador). In this work we measure for the first time, the carbon stocks and fluxes, particularly GPP, NPP, respiration and carbon allocation of Polylepis reticulata growing over 4000 m of altitude. From dendrometric measurements we have estimated the age of some trees (around 30 cm in diameter) to be more than 400 years. The temperature increase and changes in the rainfall pattern in these areas of the Andean cordillera can modify substantially the carbon fluxes between the forest and the atmosphere. From the 1151gC.m-2 year-1 uptake as GPP, 888gC.m-2 year-1 is returned to the atmosphere as growth and maintenance respiration. Most of the carbon retained as NPP is allocated to the leaves (194 from the 263 gCm-2 year-1). To produce one kg of dry biomass these trees transpire 5m3 of water. The physiological response of P. reticulata under different RCP scenarios (IPCC, 2013) has been simulated using the GOTILWA+ model. The results show drastic changes in all the scenarios. For example growing under the RCP 2.6, at the end of the present century the NPP is projected to increase up to 362 gCm-2 year-1 but, at the same time, the carbon allocated to leaves increase up to 325 gCm-2 year-1 or 90 per cent of the NPP. In that scenario the water used to grow 1 kg of dry matter is projected to increase up to 20 m3. The exploration of other climate scenarios shows more drastic changes that put at risk the survival of this emblematic species endemic of the Andean cordillera.