Dendrochronological investigation of the high Andean tree species Polylepis besseri and implications for management and conservation

Abstract

High-altitude Polylepis besseri woodlands in Bolivia are under increasing threat from human use and disturbance. Currently, there is no information regarding P. besseri growth rates, age structures or the relationship between environmental variables and growth. Such information would be useful for effective management and conservation of the remaining woodlands. We used standard dendrochronological techniques to determine the age and radial growth rates for 23 trees from two Polylepis besseri populations in Sacha Loma (mountains Uypa and Chutu Senega), and investigated the relationship between climate and radial growth. Wood samples exhibited semicircular porosity and visible tree-ring boundaries. The sample trees were young (mean age 40 years, max age 63 years) and growing slowly (<1 mm/year). Trees at Chutu Senega were older and growing more slowly than those at Uypa. The strong linearity of cumulated radial increments suggest that P. besseri may maintain consistent growth rates beyond 60 years. Our results indicate that radial growth is limited by the accumulation of reserves the year before ring formation, and that a warm period before the growing season (humid period) can increase P. besseri’s growth in the Bolivian-Tucuman biogeographic Province. It seems that local factors are more important than regional factors in these high Andean woodlands. This study improves our understanding of the biology of Polylepis and demonstrates the usefulness of dendrochronology for investigating the biotic, abiotic and anthropogenic effects on woodlands in areas lacking long term historical data.