Uni-Bayreuth grafik-uni-bayreuth



Stable Isotope Linkage of Forest WUE and Carbon Gain

TERRECO Cluster F-07

From 03/2012 to 07/2013

Principal Investigator: Dennis Ochuodho Otieno, Christiane Werner, John Tenhunen, Jong Hwan Lim
Staff: Eun-Young Jung

Abstract 2013: Temperate deciduous forest is the major terrestrial ecosystem in South Korea. Forests supply several types of services to the local communities as well as non-local communities and recently its important role in regulations of water and carbon quantity has been received public attention with regard to climate change and water shortage problems. In this regard, the quantification of water and carbon in the forest ecosystem is critical starting point of evaluation of their services. Therefore, we examined water fluxes and budgets, which can be directly linked to regulating services of forest, for temperate deciduous forests in South Korea. As the first step of this concept of the research, four specific questions were raised: (1) what determines tree water use? (2) what controls the overstory and understory transpiration (Eo and Eu)? (3) how change the contributions of Eo and Eu to the total ecosystem evapotranspiration (Eeco) over time? (4) does forest water use and water use efficiency change along elevation gradients? To answer these questions, detailed plot studies were conducted in Gwangneung (GN) and Haean Catchments. A plot in GN was a natural climax deciduous forest, ca. 200 year-old and dominated by Quercus serrata and Carpinus laxiflora forming the overstory layer. Four plots in Haean were located at different elevations, one at 450 m, two at 650 m, and one at 950 m. All four plots were young deciduous forests, ca. 30 year-old and dominated by Quercus spp., i.e., Q. mongolica, Q. dentata, and Q. serrata. For all study sites, tree water use (TWU) and forest stand transpiration were estimated from sap flux density measured by two sap flow methods, thermal dissipation probes and stem heat balance, and sapwood area determined by the increment borer. Eeco was measured only for GN forest site by the eddy covariance measurements placed at the 40 m height tower. Leaf Δ13C isotope analysis was applied for the common species of Q. mongolica for Haean sites to examine water use efficiency, which is the ratio of carbon gains and water losses through stomata, at different elevations. First, we found a general relationship of TWU to stem diameters in a sigmoid function regardless of species and elevations. This empirical relationship can be used to estimate the maximum TWU of the trees with known stem diameters. Second, we observed that the canopy development controlled not only Eo but also Eu, via changing microclimate of the understory layer. Consequently, their contributions to Eeco changed over time with changing canopy development and microclimate; for example, the contributions of Eo and Eu were decreased to 42% - 58% during monsoon rainy season, i.e., July and August. Last, stand transpiration and water use efficiency were significantly decreased with increasing elevations, thus, with decreasing mean air temperature (Ta), since a gradient in Ta caused the gradients in vapor pressure deficit and the growing season length, which determined the quantity of the annual stand transpiration. The results of the plot level studies can be utilized to calibrate and validate the spatial simulation models such as PIXGRO and HYDRUS to upscale those processes to the catchment level. Moreover, quantified forest water fluxes and budgets and defined relationships with environmental factors can be linked to estimate carbon fluxes of the forests as combining phloem sap Δ13C isotope analysis. All this information of fluxes can be the inputs for the economical evaluations of forest ecosystem services. In this way, they can help improve sustainable management strategies for the forests in South Korea.

Key words: deciduous forest, transpiration, overstory, understory, elevation gradient


Poster January 2013

last modified 2016-02-12