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Long-term drivers of change in Polylepis woodland distribution in the central Andes

Abstract:

Question: Is the modern patchy distribution of highly biodiverse Polylepis woodlands a consequence of human activity or natural fluctuations in environmental conditions? What are the consequences of changing climate for the tree genus Polylepis? Location: High central tropical Andes. Methods: We characterized the ecological baseline conditions for Polylepis woodlands over the last ca. 370 000 years through: (i) examination of fossil pollen records (Salar de Uyuni and Lake Titicaca) and (ii) a review of autecological information concerning Polylepis. Results: Fossil pollen data revealed fluctuations in the abundance (ca. 0-34%) of Polylepis pollen before the arrival of humans in South America (412 000 years ago), indicating that Polylepis did not form permanent continuous woodland before the arrival of humans and that climatic factors can drive rapid vegetation change. Autecological assessment of Polylepis revealed: (i) negative moisture balance, (ii) fire, (iii) waterlogging, and (iv) cloud cover to be critical in determining the niche space available for Polylepis. Conclusions: Polylepis niche space in the central Andes was at a maximum during warm and wet conditions in the past, but might be at a minimum during the warmer and drier than modern conditions pbkp_redicted for later this century. The sensitivity to past global climate change emphasizes the need for conservation planners to consider model pbkp_redictions of a warmer central Andes in the coming decades when developing planting schemes. Natural fluctuations in woodland abundance suggest the most effective way for conservation efforts to "mimic" the natural baseline would be to develop a reproductively connected patchwork of communities. © 2009 International Association for Vegetation Science.