Morphological-functional traits, tree diversity, growth rate and carbon sequestration in Polylepis species and ecosystems of southern Ecuador.
The species of the genus Polylepis are the most important trees of high altitude woodlands in the Andes, an area with great climatic variation from Venezuela to Argentina. In the humid climate of the Cajas Massif (southern Ecuador), four native Polylepis species form little known woodlands between 2800 and 4400 m a.s.l.: P. reticulata, P. incana, P. weberbaueri and P. lanuginosa (the latt er, endemic to Ecuador). Morphological-functional traits of these species and of another introduced (P. racemosa), and attributes at the population and ecosystem levels relevant to understanding their local distribution and the effects of global change were studied. Leaf area decreases with altitude, showing P. lanuginosa one of the largest of the genus Polylepis (17.3 cm2). High stem water content (>55%) and low stem wood density of three species suggest an ecological response to primary production limitation due to cold and/or climatic aridity. Tree species diversity (Shannon index) is moderate in the woodlands of P. reticulata and P. incana and relatively high in P. lanuginosa ones, with maxima higher than 3 bits. Tree species diversity decreases non-linearly with increasing Polylepis tree density, always greater than 400 individuals/ha and frequently more than 1000 individuals/ha. Aboveground biomass is a very variable ecosystem attribute and remarkable in some woodlands (about 200 Mg C/ha). The diameter growth rate at breast height of P. reticulata after seven years is 1.2 mm/year, and the average carbon sequestration rate is 2.6±0.3 Mg C.ha-1.year-1, outstanding for a slow-growing genus. Polylepis woodlands conservation is pertinent to preserve threatened high Andean biodiversity and mitigate climate change by its ability to retain carbon in biomass.