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

Gosling, William D.; Hanselman, Jennifer A.; Knox, Christoper; Valencia, Bryan G. and Bush, Mark B. (2009). Long term drivers of change in Polylepis woodland distribution in the central Andes. Journal of Vegetation Science, 20(6) pp. 1041–1052.

DOI: https://doi.org/10.1111/j.1654-1103.2009.01102.x


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 characterise 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 reveal fluctuations in the abundance (c. 0-34%) of Polylepis pollen prior to the arrival of humans in South America (>12,000 years ago). Indicating that Polylepis did not form permanent continuous woodland prior to the arrival of humans and that climatic factors can drive rapid vegetation change. Autecological assessment of Polylepis reveals: i) negative moisture balance, ii) fire, iii) waterlogging, and iv) cloud cover to be critical to 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 predicted for later this century. The sensitivity to past global climate change emphasises the need for conservation planners to consider model predictions 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.

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