Water consumption and carbon capture by trees of an evergreen and a deciduous mountain forest as functional indicators of slow environmental changes in South Ecuador

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This transfer project develops a module of a multifactorial indicator prototype for global change effects in an evergreen mountain forest in South Ecuador. It uses water and carbon relations of trees as primary functional indicators of subtle environmental changes, which cannot be observed directly. Acquisition of carbon by a tree and its concomitant water loss by transpiration is coupled as water use efficiency (WUE), which as a parameter integrates two ecophysiological processes and should exhibit a high sensitivity to environmental conditions. The project C5 is based on a new model allowing computation of the net CO2 uptake by the entire crown. Parameterization of the model is by data of leaf gas exchange, total water consumption of the tree, and structural data of the crown (provided by project C6). In collaboration with project C6, a study plot (10 x 100 m) was established in the forest, including two towers (30 and 36 m high) with two platforms each. The platforms are used for campaigns of gas exchange measurements in the crowns of eight trees. These trees and 13 more on the stretch between the towers are equipped with sap flow sensors for continuous long-term measurements of the daily water consumption. WUE and other tree-specific physiological important parameters like the unexpected high nocturnal transpiration are measured on different tree species which according to their functional type exhibit different sensitivity to environmental changes. Furthermore, the crown specific WUE and the total water consumption of the trees will be used to calculate total photosynthetic net carbon gain. The described measurements will be supplemented by data on stem growth, longevity of leaves and long-term water relations (13C discrimination data). Due to administrative and logistic problems, first measurements started only 1.5 years ago. For the long-term seasonal comparison and the differentiation between transitory changes and long-term tendencies, continuous measurements are required for at least two years. The three tree species where data are already available over 18 months showed a decreasing water consumption which could be attributed to an increase in precipitation and relative humidity. This tendency and the different sensitivities of tree species should be proven with the remaining 8 tree species (18 trees) from which data are available so far for 9 or 11 months.Project C6 investigates evapotranspiration above the canopy on the stretch between the two towers with the help of a scintillometer, an approach which requires the data from project C5 for interpretation. The combination of the projects C5 and C6 will result in the development of the indicator for the mountain rain forest.