Fire and climate: contrasting pressures on tropical Andean timberline species
Journal of Biogeography
This is the peer reviewed version of the following article: Bush, M. B., Alfonso-Reynolds, A. M., Urrego, D. H., Valencia, B. G., Correa-Metrio, Y. A., Zimmermann, M., Silman, M. R. (2015), Fire and climate: contrasting pressures on tropical Andean timberline species. Journal of Biogeography, 42: 938–950. doi: 10.1111/jbi.12470, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/jbi.12470/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Reason for embargo
Aim: The aim was to test competing hypotheses regarding migration of the Andean timberline within the last 2000 years. Location: The upper forest limit in Manu National Park, Peru. Methods: A randomized stratified design provided 21 soil profiles from forested sites just below the timberline, 15 from puna grassland sites just above the timberline and 15 from the transitional habitat at the puna–forest boundary. From each profile a surface sample (hereafter modern) and a sample from the base of the organic horizon (hereafter historical) were collected. Pollen and charcoal were analysed from the modern and historical layers of the 51 soil profiles. A chronological framework was provided by 24 14C dates. Data were ordinated as modern and historical groups and the temporal trends illustrated by Procrustes rotation. Results: The organic layer from the soil profiles represented the last 600–2000 years. Fire was much more abundant in all habitat types (puna, transitional and forested) in the modern compared with the historical groups. Samples that had historically been in puna just above the timberline showed encroachment by woody species. Samples that had been forested were still classified as forest but their composition had become more transitional. Sites that were transitional appeared to represent a new or expanded class of sites that was far less abundant historically. Main conclusions: Our results are consistent with ongoing warming causing an upslope migration of species, although not necessarily of the timberline. Weedy fire-tolerant species are spreading upslope, creating a transitional forest, softening the boundary between forest and puna. Simultaneously, fire introduced to improve grazing outside the park has increasingly penetrated the forest and is causing the upper timberline to shift towards more fire-tolerant and weedy species. Consequently, both the form of the ecotone between forest and grassland and the species composition of these forests is changing and is expected to continue to change, representing a shifting baseline for what is considered to be natural.
Gordon and Betty Moore Foundation Andes-to-Amazon programme
Blue Moon Fund
National Science Foundation
Department of Biological Sciences; Florida Institute of Technology; Melbourne FL USA Department of Biological Sciences; Florida Institute of Technology; Melbourne FL USA Department of Biological Sciences; Florida Institute of Technology; Melbourne FL USA Geography, College of Life & Environmental Sciences; University of Exeter; Exeter UK Department of Biological Sciences; Florida Institute of Technology; Melbourne FL USA CEPSAR; The Open University; Milton Keynes UK Instituto de Geología; Universidad Nacional Autónoma de México; Ciudad Universitaria; Mexico City Mexico Department of Forest and Soil Sciences; University of Natural Resources and Life Sciences Vienna; Vienna Austria Department of Biology and Center for Energy; Environment and Sustainability; Wake Forest University; Winston Salem NC USA
Copyright © 2015 John Wiley & Sons Ltd.
Vol. 42, Iss.5, pp. 938 - 950, May 2015