title: A novel dendrochronological approach reveals drivers of carbon sequestration in tree species of riparian forests across spatiotemporal scales.
abstract: Aboveground carbon (C) sequestration in trees is important in global C dynamics, but reliable techniques for its modeling in highly productive and heterogeneous ecosystems are limited. We applied an extended dendrochronological approach to disentangle the functioning of drivers from the atmosphere (temperature, precipitation), the lithosphere (sedimentation rate), the hydrosphere (groundwater table, river water level fluctuation), the biosphere (tree characteristics), and the anthroposphere (dike construction). Carbon sequestration in aboveground biomass of riparian Quercus robur L. and Fraxinus excelsior L. was modeled (1) over time using boosted regression tree analysis (BRT) on cross-datable trees characterized by equal annual growth ring patterns and (2) across space using a subsequent classification and regression tree analysis (CART) on cross-datable and not cross-datable trees. While C sequestration of cross-datable Q. robur responded to precipitation and temperature, cross-datable F. excelsior also responded to a low Danube river water level. However, CART revealed that C sequestration over time is governed by tree height and parameters that vary over space (magnitude of fluctuation in the groundwater table, vertical distance to mean river water level, and longitudinal distance to upstream end of the study area). Thus, a uniform response to climatic drivers of aboveground C sequestration in Q. robur was only detectable in trees of an intermediate height class and in taller trees (>21.8m) on sites where the groundwater table fluctuated little (≤0.9m). The detection of climatic drivers and the river water level in F. excelsior depended on sites at lower altitudes above the mean river water level (≤2.7m) and along a less dynamic downstream section of the study area. Our approach indicates unexploited opportunities of understanding the interplay of different environmental drivers in aboveground C sequestration. Results may support species-specific and locally adapted forest management plans to increase carbon dioxide sequestration from the atmosphere in trees.
authors.affiliation: Department of Ecology, Ecosystem Science/Plant Ecology, Technische Universität Berlin, Rothenburgstraße 12, 12165 Berlin, Germany; Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), 14195 Berlin, Germany. Electronic address: isaak.rieger@tu-berlin.de.
authors.forename: Isaak
authors.initials: I
authors.lastname: Rieger
authors.affiliation: Department of Ecology, Ecosystem Science/Plant Ecology, Technische Universität Berlin, Rothenburgstraße 12, 12165 Berlin, Germany; Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), 14195 Berlin, Germany. Electronic address: kowarik@tu-berlin.de.
authors.forename: Ingo
authors.initials: I
authors.lastname: Kowarik
authors.affiliation: WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Zürcherstraße 111, CH-8903 Birmensdorf, Switzerland. Electronic address: paolo.cherubini@wsl.ch.
authors.forename: Paolo
authors.initials: P
authors.lastname: Cherubini
authors.affiliation: Department of Ecology, Ecosystem Science/Plant Ecology, Technische Universität Berlin, Rothenburgstraße 12, 12165 Berlin, Germany; Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), 14195 Berlin, Germany; Biocenter Klein Flottbek, Biodiversity of Useful Plants, Universität Hamburg, Ohnhorststraße 18, 22609 Hamburg, Germany. Electronic address: arne.cierjacks@tu-berlin.de.
authors.forename: Arne
authors.initials: A
authors.lastname: Cierjacks
mesh_terms: D001317:Austria; D018533:Biomass; D002244:Carbon; D057965:Carbon Sequestration; D065928:Forests; D031661:Fraxinus / Q000378:metabolism*; D029963:Quercus / Q000378:metabolism*; D045483:Rivers; D014197:Trees / Q000378:metabolism
chemical_list: D002244:Carbon
keywords: Boosted regression tree; Carbon sequestration; Classification and regression tree; Climate; Danube River; Dendrochronology