title: Elevation alters ecosystem properties across temperate treelines globally.
abstract: Temperature is a primary driver of the distribution of biodiversity as well as of ecosystem boundaries. Declining temperature with increasing elevation in montane systems has long been recognized as a major factor shaping plant community biodiversity, metabolic processes, and ecosystem dynamics. Elevational gradients, as thermoclines, also enable prediction of long-term ecological responses to climate warming. One of the most striking manifestations of increasing elevation is the abrupt transitions from forest to treeless alpine tundra. However, whether there are globally consistent above- and belowground responses to these transitions remains an open question. To disentangle the direct and indirect effects of temperature on ecosystem properties, here we evaluate replicate treeline ecotones in seven temperate regions of the world. We find that declining temperatures with increasing elevation did not affect tree leaf nutrient concentrations, but did reduce ground-layer community-weighted plant nitrogen, leading to the strong stoichiometric convergence of ground-layer plant community nitrogen to phosphorus ratios across all regions. Further, elevation-driven changes in plant nutrients were associated with changes in soil organic matter content and quality (carbon to nitrogen ratios) and microbial properties. Combined, our identification of direct and indirect temperature controls over plant communities and soil properties in seven contrasting regions suggests that future warming may disrupt the functional properties of montane ecosystems, particularly where plant community reorganization outpaces treeline advance.
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå 90187, Sweden.
authors.forename: Jordan R
authors.initials: JR
authors.lastname: Mayor
authors.affiliation: Center for Macroecology, Evolution and Climate, The Natural History Museum of Denmark, University of Copenhagen DK-2100, Copenhagen Ø, Denmark.|The Rocky Mountain Biological Laboratory, PO Box 519, Crested Butte, Colorado 81224, USA.
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Sanders
authors.affiliation: Center for Macroecology, Evolution and Climate, The Natural History Museum of Denmark, University of Copenhagen DK-2100, Copenhagen Ø, Denmark.|The Rocky Mountain Biological Laboratory, PO Box 519, Crested Butte, Colorado 81224, USA.
authors.forename: Aimée T
authors.initials: AT
authors.lastname: Classen
authors.affiliation: School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PT, UK.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Bardgett
authors.affiliation: Laboratoire d'Ecologie Alpine, CNRS UMR 5553, Université Grenoble Alpes, CS 40700, FR-38058 Grenoble Cedex 9, France.|CARRTEL, UMR 0042 Université Savoie Mont-Blanc - INRA, FR-73376 Le Bourget-du-Lac, France.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Clément
authors.affiliation: Centro de Investigación en Ecosistemas de la Patagonia (CIEP) R10C1003, Universidad Austral de Chile, Camino Baguales s/n, Coyhaique 5951601, Chile.
authors.forename: Alex
authors.initials: A
authors.lastname: Fajardo
authors.affiliation: Laboratoire d'Ecologie Alpine, CNRS UMR 5553, Université Grenoble Alpes, CS 40700, FR-38058 Grenoble Cedex 9, France.
authors.forename: Sandra
authors.initials: S
authors.lastname: Lavorel
authors.affiliation: Center for Macroecology, Evolution and Climate, The Natural History Museum of Denmark, University of Copenhagen DK-2100, Copenhagen Ø, Denmark.|Umeå University, Department of Ecology and Environmental Sciences, Umeå 90187, Sweden.
authors.forename: Maja K
authors.initials: MK
authors.lastname: Sundqvist
authors.affiliation: Institute of Ecology, University of Innsbruck, 6020 Innsbruck, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Bahn
authors.affiliation: Center for Macroecology, Evolution and Climate, The Natural History Museum of Denmark, University of Copenhagen DK-2100, Copenhagen Ø, Denmark.
authors.forename: Chelsea
authors.initials: C
authors.lastname: Chisholm
authors.affiliation: Landcare Research, PO Box 69040, Lincoln 7640, New Zealand.|Institute of Environmental Sciences, Leiden University, Einsteinweg 2, 2333 CC Leiden, The Netherlands.
authors.forename: Ellen
authors.initials: E
authors.lastname: Cieraad
authors.affiliation: Department of Geography, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Ze'ev
authors.initials: Z
authors.lastname: Gedalof
authors.affiliation: Laboratoire d'Ecologie Alpine, CNRS UMR 5553, Université Grenoble Alpes, CS 40700, FR-38058 Grenoble Cedex 9, France.
authors.forename: Karl
authors.initials: K
authors.lastname: Grigulis
authors.affiliation: Hokkaido University, Faculty of Environmental Earth Science, Sapporo 060-0810, Japan.
authors.forename: Gaku
authors.initials: G
authors.lastname: Kudo
authors.affiliation: Department of Methodology &Statistics, Utrecht University, 3584 CH Utrecht, The Netherlands.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Oberski
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå 90187, Sweden.
authors.forename: David A
authors.initials: DA
authors.lastname: Wardle
mesh_terms: D000531:Altitude; D044822:Biodiversity; D002244:Carbon / Q000378:metabolism; D065928:Forests; D009584:Nitrogen / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology; D013696:Temperature; D014197:Trees / Q000378:metabolism*; D065929:Tundra
chemical_list: D012987:Soil; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen