Identifying environmental drivers of carbon and water fluxes and the origin of atmospheric water over a tropical mountain rainforest in Sulawesi, Indonesia

• Applicant: Professor Dr. Alexander Knohl
• Subject Area: Forestry
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 247499602

Tropical rainforest in Southeast Asia are important components of the regional climate system as they absorb carbon dioxide and contribute to atmospheric moisture via evapotranspiration. Direct measurements of carbon dioxide and water vapour fluxes using the eddy covariance technique are, however, scarce in that region. Our previous measurements at the Bariri site, a tropical mountain rainforest in Central Sulawesi/Indonesia, revealed an unexpectedly large carbon uptake and large evapotranspiration. Thus, we now propose in the extension proposal to investigate a number of methodical questions and to test several biological hypotheses that could explain the observations.In work package WP1 we want to (a) improve the measurements at nighttime, which are often a source of underestimation of ecosystem respiration and thus overestimation of net carbon uptake, by adding a CO2 and H2O profile system, (b) to test the hypotheses that relatively low temperature due to the high elevation site (1440 m a.s.l.) with high radiation and water availability results in high net carbon uptake, and (c) to test the hypotheses that diffuse radiation has an carbon uptake enhancing effect. WP1 will combine eddy covariance measurements and additional meteorological measurements at the Bariri site with ecosystem system modeling using the multi-layer biophysical model CANVEG.In WP 2 we want to focus on the hypothesis that local water recycling between forest and atmosphere results in high water availability (also during the dry season). We aim to achieve this by using stable water isotope measurements at the Bariri site. For that we will (a) carry out continuous measurements of atmospheric water vapour isotope measurements over the tropical rainforest in Bariri, (b) estimate the water isotope composition of evapotranspiration using a flux-gradient approach, (c) validate our estimate with independent measurements of leaf, xylem, soil water and precipitation, and (d) integrate our measurements to ecosystem scale by improving/developing a water isotope enabled version of the multi-layer biophysical model CANVEG.We anticipate that our research will substantially improve our understanding of the carbon and water fluxes at the tropical mountain rainforest in Central Sulawesi. This is particularly of importance as this region has been selected as the only pilot project in Indonesia of the UN REDD program and reliable numbers of carbon uptake by the intact rainforest are urgently needed as reference.

• DFG Programme: Research Grants