Project

Back to overview

Give and take: How much water does soil retain for trees?

Applicant Meusburger Katrin
Number 185093
Funding scheme Project funding (Div. I-III)
Research institution Swiss Federal Research Inst. WSL Direktion
Institution of higher education Swiss Federal Institute for Forest, Snow and Landscape Research - WSL
Main discipline Pedology
Start/End 01.10.2019 - 30.09.2023
Approved amount 266'964.00
Show all

All Disciplines (2)

Discipline
Pedology
Hydrology, Limnology, Glaciology

Keywords (11)

soil water balance model; defoliation; Switzerland; forest health; isotopes; forest; ecohydrology; drought; soil moisture dynamics; unsaturated zone; plant water stress

Lay Summary (German)

Lead
Wälder benötigen Wasser. Dieses fällt in der Schweiz mehrheitlich durch Niederschlag, wird im Waldboden gespeichert und steht dadurch den Bäumen zur Verfügung. Längere Trockenperioden können zu Verschlechterungen der Waldgesundheit führen. Welche Rolle dem Boden im Hinblick auf die Auswirkungen von Trockenheit auf Schweizer Wälder zukommt, ist bisher noch nicht erforscht.
Lay summary

Ziel dieses Forschungsprojektes ist es zu einem verbesserten Verständnis beizutragen welche Faktoren zu trockenheitsbedingtem Stress von Bäumen in Schweizer Wäldern führen.

Als Datengrundlage werden wir die Bodenfeuchte- und Wasserpotentialdaten der schweizweit verteilten Flächen der langfristigen Waldökosystemforschung (LWF, total 19 Flächen) nutzen. Mithilfe dieser Datengrundlage werden wir ein bodenhydrologisches Modell kalibrieren um ein Inventar der Wasserverfügbarkeit in Schweizer Wäldern über die letzten 20 Jahre zu erstellen. Die routinemässige Beprobung der Bodenlösung auf den LWF Flächen wird durch Isotopenmessungen ergänzt und zusätzlich auch auf das Xylemwasser erweitert. Die Isotopenmessungen erlauben einerseits die Verweilzeiten des Bodenwassers und andererseits eine präzisere Beschreibung der Interaktionen zwischen Boden und Baum abzuleiten und in das Modell zu integrieren.

Basierend auf dem quantitativen Bodenwasserinventar und der Entwicklung der Waldgesundheit über den gleichen Zeitraum wollen wir Schlussfolgerungen zu den Auswirkungen von Trockenheit auf die Wasserverfügbarkeit und die Waldgesundheit ziehen.

Direct link to Lay Summary Last update: 13.12.2019

Responsible applicant and co-applicants

Employees

Project partner

Abstract

Efforts to assess the broad-scale impacts of climate extreme conditions on forest health often fall short due to the omission of the overprinting effect of soil properties on plant water availability. More explicit consideration of soil water processes in the unsaturated zone may significantly enhance the explanatory power of models seeking to disentangle the impacts of climate extreme conditions on forest health. However, the need for water further depends on plant type, especially on the ontogenesis stage of particular plants. Therefore, it is also crucial to assess proxies of forest health to relate meteorological extreme conditions to patterns of plant physiological stress. This project aims to establish this link between climate extreme conditions and impacted forest health by filling the mentioned soil gap and mapping proxies of forest health status.The core part of the proposed research will deal with the parameterization of a physically based soil water balance model on i) plot scale using stable water isotopes and in-situ soil moisture content and soil water potential measurements and ii) Swiss scale by regionalizing soil hydraulic- and canopy parameters. At the plot scale, the soil water balance model will profit from the wealth of data monitored within the Long-term Forest Ecosystem Research program (LWF) across Switzerland (corresponding to ICP Forest level II plots). For the application at the Swiss scale, the soil hydraulic parameters (Mualem-van Genuchten equation) will be calculated for 1250 soil profiles using suitable pedo-transfer functions. The regionalization of soil hydraulic properties to Swiss scale will be accomplished by the digital soil mapping technique Random Forest that was recently extended to account for the spatial location of points (geography) together with a large set (n>229) of spatial covariates. The soil water balance model will be forced by daily meteorological data and model validation will be accomplished through an independent network of soil water potential measurements at 40 forest sites. Since there is a considerable lack of understanding to which extent plants rely on water from deeper soil layers as well as limited quality of soil water predictions for these deeper layers, we aim to enlighten this aspect with the aid of stable water isotopes measurements in precipitation-, soil solution- (0, 15, 50, 80cm depth) and xylem water samples. Stable water isotopes will serve to trace i) soil water movement through the unsaturated zone and ii) sources of plant water uptake. Unmixing the isotopic signature of the xylem water will provide insights to plant water sources and spatiotemporally varying water use strategies that will help to understand which meteorological conditions lead to plant physiological stress.Crown defoliation will serve as a proxy for forest health. Linear spectral unmixing of Landsat and Sentinel-2ab scenes (2000-2018) is a promising sub-pixel classification technique that yields abundance maps of typical forest components and allows to distinguish between green (photosynthetic) and non-green (dead materials) contributions to canopy absorbance. The remote-sensing derived patterns of the non-green part of the crown aligned with crown defoliation observations at 55 sites across Switzerland (since 1985) serves a spatiotemporal measure of forest health condition. Finally, intersecting the above ground crown defoliation with the below-ground soil water processes will create the basis to infer the effect of climate extreme conditions on forest health status via a Bayesian hierarchical model.Our findings will define a baseline of soil water stress and related forest health condition and as such significantly contribute to the discussion on forest sensitivity and resilience to soil water stress caused by climate extreme conditions. The proposed methods have the potential to develop into a monitoring tool at Swiss scale and will represent a reliable basis for climate change scenarios.
-