C5 Water consumption and carbon capture by trees of an evergreen and a dry forest in the Andes of South Ecuador as functional indicators of slow environmental changes.
PI(s) for this project:
Prof. Dr. Dr. h.c. Erwin Beck
This transfer project contributes to the development of a multifactorial indicator prototype for global change effects. It uses water and carbon relations of trees as primary functional indicators of subtle environmental changes which cannot be directly observed. Acquisition of carbon by a tree and its concomitant water loss by transpiration is coupled as water use efficiency (WUE), which as a parameter integrating two ecophysiological processes should display a high sensitivity to ambiental conditions. The project is based on a new model allowing computation of the entire crown. Parameterization of the model is by data of leaf gas exchange, total water loss, and structural data of the crown. Total water consumption will be determined either by stem flow monitoring or by the D2O injection method. Net carbon gain by the entire crown can be calculated from a crown-specific WUE. The described measurements will be supplemented by data on stem growth, phenology (longevity of leaves and foliage dynamics), long-term water relations (13C discrimination data) and tree hydrology (natural abundance of deuterium). To extend the indicator from the single tree scale to a wider area, project C5 will collaborate with project C6 which will investigate WUE using multispectral satellite and airborne data.
For calibration transfer functions to remotely sensed data must be developed. Since Eddie covariance analysis cannot be used, project C6 will measure atmospheric dynamics of heat and water vapour above the canopy of an assemblage of such trees by scintillometry. These measurements shall be calibrated by C5. Of all trees on the study plots total transpiration will be measured and correlated with simultaneously recorded scintillometer data. Thus projects C5 and C6 will use the same plots and trees. Using the calibrated scintillometer data, project C6 will up-scale the functional indicator WUE to the landscape level. Because of their general applicability, functional indicators like WUE are especially useful for modelling approaches.
Project C5 is conducted on two study sites: Reserva Biológica San Francisco (RBSF) in the tropical mountain forest (WP1), and Reserva Laipuna the dry forest (WP2).
WP1: Water use efficiency (WUE) on the tree level
For determination of the water use efficiency (ratio of carbon to water fluxes) of indigenous trees, we are investigating water consumption on the tree level (sap flow) and transpiration and net carbon uptake (gas exchange measurement) on the leaf level. For sap flow measurement, 20 trees on a stretch of 100 m are equipped with 3 Granier sensors each. The measured tree species are Vismia tomentosa, Podocarpus oleifolia, Spirotheka rosea, Tapirira cf. guianensis, Graffenrieda emarginata and some representatives of the Lauraceae. For gas exchange measurements (leaf level), porometry is used. Two 30 m high towers are constructed with platforms which allow access to the full crown of several tree species. Ecophysiologically important traits of leaves from the sun- and the shade crown will be monitored, too. The towers will be also used to for laser scintillometer measurements of project C6.
Sap flow measurement on V. tomentosa Observation tower at the RBSF
WP2: Tree water use in the dry forest of Laipuna
Tropical dry forests such as the Reserva Laipuna are characterized by low annual rainfall and a pronounced seasonality in distribution of precipitation. To cope with seasonal water shortages trees use different strategies such as reduced transpiration rates, water uptake deep soil horizons, and internal water storage. With this project we aim to analyze ecohydrological processes at the tree and stand level in the dry forest of the Reserva Laipuna. We combine sap flow measurements and stable isotope approaches (deuterium tracing and natural abundance of deuterium in soil and plant water). Target tree species of the project are Eriotheca ruizii, Ceiba trichistandra, Bursera graveolens, Erythrina velutina and evergreen species (e.g. Capparis), which will be studied along an altitudinal transect of 600 – 1200 m asl. This project works closely together with project A2 (dendroecology) and C6 (remote sensing).
Reserva Laipuna dry season Reserva Laipuna rainy season