Assessments of vulnerability of mature and secondary forests to climatic water stress in Southeast Asia – CWSSEA

We use a suite of techniques to measure 1) past responses of forests to drought (using tree-rings and isotopes analysis), 2) present responses of forests by quantifying water and carbon fluxes, hydraulic properties, safety margin, canopy physiology and canopy functional diviersity, 3) future forest responses using an ecosystem model to estimate forest productivity under various climate change scenarios.

We proposed to perform studies on water and carbon budgets and compare them with ecosystem fluxes measured by the eddy covariance system (gas exchange parameters and related functional and hydraulic traits which explain plant functions within each forest). We also performed some carbon dynamics which will provide us with some insights into how productivity of these forests may differ across seasons.

Originally, we proposed to use a dynamic global vegetation model (DGVM) that takes into account the diverse functional traits of various forests to estimate future climate changes. However, after several discussions among teams, we may not have sufficient past climate data that can be used to validate the model. Instead, we will utilize a well-known ecosystem model to estimate the responses of forests to future climate change. Additionally, we will upscale the results to the continental region covering the studied forests by incorporating some remote-sensing data to illustrate the spatio-temporal changes of forest productivity due to predicted climate changes. We believe that such results will highlight the importance of forest of different types and stages in this region and how climate change will affect them in the future, which will benefit policy makers in areas of forest conservation and restoration and climate change adaptation.

In year 1, Domec performed some of the laboratory measurements. In year 2, Domec mentored a PhD student from Chulalongkorn University (Weerapong Unawong) in Thailand and recoded and used a multilayered hydraulically driven soil–vegetation–atmosphere carbon and water transfer model that was specifically re-designed to represent processes common to vascular plants, so that ecosystem– atmosphere exchange may be captured by the same processes for different species. Hydraulic traits used to force the model were measured by Domec and also the PhD student from Chulalongkorn University who visited INRA and went with Domec at Duke University (USA) in October 2019. The student learned how to measure plant vulnerability to embolism, which describes the percentage loss of hydraulic conductivity as a function of xylem tension and applied the technique on tree samples from natural and secondary forests in Thailand. Those data were then analyzed by Dr. D. Vidal who also was hired on the project between October 2019 and Mars 2020. The work performed by D. Vidal was submitted to Tree physiology (see list below) and has been accepted pending revisions.

Duty for Year 3: around 8,200 euros are left in the budget, which will be used to attend several international meetings (if COVID 19 allows it) and to finish the modeling work with colleagues from Duke University.

Vidal D.F., Augusto L., Bakker M.R., Trichet P., Puzos L, J. C Domec. 2020. Understorey-overstorey biotic interactions are key factors of Pinus pinaster functioning in oligotrophic conditions. Tree Physiology Accepted with revisions
Bonetti S, Breitenstein D., Fatichi S., Domec JC., and D. Or. 2020. Persistent decay of fresh xylem hydraulic conductivity varies with pressure gradient and marks plant responses to injury. Submitted to Plant, Cell and Environment June 2020.
Domec J.C., King J.S., Carmichael M.J., Treado Overby A., Wortemann R, SmithW. K., Miao G, Noormets A., and D.M. Johnson. 2020. Root water gates provide new functional insights into plant responses and adaptations to drought, flooding and salinity stresses. Submitted to Plant Physiology July 2020


Bonetti S., D. Breitenstein, S. Fatichi, J-C Domec and D. Or. The hydraulic conductivity of wounded xylem. European Geosciences Union, Vienna, May 2020 EGU2020-5856-D693. Poster
Fischer M., G. Katul, A. Noormets, G. Pozníková, J.h. Domec, M. Orság, M. Trnka, J. King . Deriving the sensible heat flux from the air temperature time-series through the flux-variance and the surface renewal methods. European Geosciences Union, Vienna, May 2020. EGU2020-5856. Oral.
Domec JC. 2018. The canopy belowground: establishing a direct link between plant root functioning (including hydraulic lift) and ecosystem water and carbon fluxes. (Invited presentation) University Program of ecology seminar Duke University, November 27, 2018.
Domec JC, J. Swenson, G. Katul, D. Johnson, N. McDowell, R. Jackson, S. Palmroth, J. Ogée, A. Porporato, R. Oren. 2018. Can models of plant physiological processes provide a good understanding of mechanisms underlying vegetation responses to climate? Invited presentation at the Annual Conference for Science and the Environment – Weizmann Institute of Science, Israel - June 20-21 2018.

Climatic water stress, such as droughts and warmer temperatures, may accelerate forest mortality. Increasesof frequency and intensity of drought events are predicted to increase in the monsoon Southeast Asia. Suchincreases could drive rapid and large-scale shifts in forest structure and species composition. Moreover, thedrought-induced mortality events may cause dramatic decreases in carbon stored by tropical forests whichare hotspots of biodiversity and a persistent carbon sink in the global carbon cycle.Secondary forests represent the majority of forested areas in the tropics and have higher carbonaccumulation rate than mature forests. However, compared to mature forests, we know relatively little abouttree functioning and ecophysiology of secondary forest ecosystem. Many forests in Southeast Asia consist ofvarious stages of ecological succession which are challenging to modelling climate-vegetation feedbacks inthis region. Differences in species composition of mature and secondary forests can further complicate ourunderstanding of how water will respond to climatic water stress in the future. Because changes in droughtfrequency and severity could have large consequences on forest structure and functioning, we need a betterunderstanding of the vulnerability of tropical forests to drought in order to more accurately predict globalcarbon and water cycling in light of climate change.Globally, canopy transpiration is the major component of total water transfer from forests to the atmosphere.Canopy transpiration is often used to estimate mean canopy stomatal conductance which is central tomodelling carbon uptake by forests. Differences in species compositions of mature and secondary forestsmay result in different canopy transpiration which can influence hydrologic and carbon cycles of theseforests. With limited understanding of water and carbon cycling in Southeast Asian secondary forests,especially under climatic water stress, uncertainty in climate-vegetation models may increase, leading toinaccurate forecast of future changes in the global water and carbon cycles.With these regards, we propose to estimate canopy transpiration and evaluate its variation with climaticconditions in a mature and a secondary forests in Thailand. We will also investigate species-specificresponses to water stress by assessing tree hydraulics and drought vulnerability of the dominant species ineach forest. Furthermore, we will explore the degree of soil water partitioning of species within each forest toenhance our understating of climate change impact on forest structure and function of both forest types.Additionally, this study will be the first, to our knowledge, that quantifies canopy transpiration in secondaryforests in Southeast Asia. The outcome can be used to plan restoration projects, as well as to promote thevalues of secondary forests worldwide.