Water balance and productivity of a Mediterranean oak woodland : Quantifying understory vegetation impacts by development of a stable oxygen isotope partitioning approach
type: CreativeWork
description: Semi-arid ecosystems cover large areas world-wide and contribute about 40% to global gross primary production (GPP). The major driving factor of GPP in these ecosystems is water availability; since annual precipitation pattern show periodical summer droughts and evapotranspiration losses are high. Hence, understanding seasonal vegetation-soil-water feedbacks is vitally important. This thesis aims at disentangling vegetation impacts on water and carbon cycling of a Mediterranean savanna-type oak woodland. Special focus was laid on the seasonal understory impact on net ecosystem fluxes, soil water distribution and tree-understory interactions. Moreover, the impact of altered precipitation pattern and drought intensity on ecosystem functioning was assessed, as these phenomena are predicted to increase by climate change scenarios in these ecosystems. To achieve these aims, classical ecophysiological measurements, plant community and structural observations as well as eddy-covariance technique were combined with a novel stable oxygen isotope partitioning approach. Stable oxygen isotopes are valuable tracers for water movements within the ecosystem, but due to methodological restrictions in the past, it was necessary to validate modeling approaches and derive field sampling protocols for model input parameters. Therefore, a measurement set-up was developed coupling branch and soil chambers with an H2O laser spectrometer, enabling direct, high frequent measurements of δ18O signatures of evaporative fluxes and, to my best knowledge, the first validation of the Craig and Gordon model under heterogeneous field conditions. Thereby it was possible to assess multiple effects of understory vegetation on ecosystem water cycle and productivity. Although understory transpiration strongly contributed to ecosystem evapotranspiration, beneficial effects of the understory vegetation were dominant as herbaceous biomass strongly increased rain infiltration, diminished soil evaporation and…
abstract: Semi-arid ecosystems cover large areas world-wide and contribute about 40% to global gross primary production (GPP). The major driving factor of GPP in these ecosystems is water availability; since annual precipitation pattern show periodical summer droughts and evapotranspiration losses are high. Hence, understanding seasonal vegetation-soil-water feedbacks is vitally important. This thesis aims at disentangling vegetation impacts on water and carbon cycling of a Mediterranean savanna-type oak woodland. Special focus was laid on the seasonal understory impact on net ecosystem fluxes, soil water distribution and tree-understory interactions. Moreover, the impact of altered precipitation pattern and drought intensity on ecosystem functioning was assessed, as these phenomena are predicted to increase by climate change scenarios in these ecosystems. To achieve these aims, classical ecophysiological measurements, plant community and structural observations as well as eddy-covariance technique were combined with a novel stable oxygen isotope partitioning approach. Stable oxygen isotopes are valuable tracers for water movements within the ecosystem, but due to methodological restrictions in the past, it was necessary to validate modeling approaches and derive field sampling protocols for model input parameters. Therefore, a measurement set-up was developed coupling branch and soil chambers with an H2O laser spectrometer, enabling direct, high frequent measurements of δ18O signatures of evaporative fluxes and, to my best knowledge, the first validation of the Craig and Gordon model under heterogeneous field conditions. Thereby it was possible to assess multiple effects of understory vegetation on ecosystem water cycle and productivity. Although understory transpiration strongly contributed to ecosystem evapotranspiration, beneficial effects of the understory vegetation were dominant as herbaceous biomass strongly increased rain infiltration, diminished soil evaporation and…
author: Dubbert, Maren
date published: 2014-07-25
date modified: 2026-07-27T18:49:36Z
provider: Universität Bayreuth
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Universität Bayreuth