Ecosystem Water Use: A Concept Linking Water and Carbon Fluxes Jiquan Chen Landscape Ecology & Ecosystem Science (LEES) Lab University of Toledo Feb. 21, 2005 Flux Towers NEE c & NEE H2O Average diurnal fluxes of CO 2 and H 2 O in Jul., Aug., and Sept. in 1999 in a 20 and a 500 year-old Douglas-fir forest (WA). Only data from good fetch ( o ) directions were used. Negative and positive values indicate uptake and loss, respectively. Chen et al. 2002 Measurement Year Stand40YR450YR20YR450YR Carbon (g C.m -2.day -1 ) July August September Overall Water (mm.day -1 ) July August September Overall Average daily net exchange of carbon and water in Jul., Aug., and Sept. of 1998 and 1999 at three Douglas-fir forests of different ages (20, 40, and 450 year-old) in S. WA. Chen et al. 2002 WUE is traditionally used as the amount of photosynthetic product produced per unit water evaporated, but a number of other definitions have been given to this term as well, depending on the purposes of the experiment. In this study, we define WUE e as the ratio of net ecosystem exchange of carbon (F c ) to evapotranspiration (ETor F H2O ): Ecosystem Water Use Efficiency (WUE e ) at Four Measuring Periods of 3 Douglas-fir Stands Dry yearWet year WUE e of the old-growth forest was significantly greater in the drier summer of 1998 (2.7 mg.g -1 ) than in 1999 (1.0 mg.g -1 ). WUE e of the young stand was significantly lower than that of old-growth forest.Conclusions Dry yearWet year Scanlon and Albertson 2004 How does WUE e change with stand age (succession)? How does WUE e vary among ecosystems (disturbance)? A landscape is composed of a variety of ecosystems differing in type, age, size, shape, and spatial arrangement. Two questions are: Methods Methods A combination of direct measurements, remote sensing images, and ecosystem models. Pine BarrensMature red pineMature hardwood Young red pine Mature red pine Cumulative seasonal evaportranspiration (ET) at five ecosystems MRP YRP PB MHW CC W UE, mg CO 2 g-1 H2 O WUE e of Five Ecosystems in the CNF of Northern WI R WUE e among 5 ecosystems Water use efficiency and stand age At leaf level, instantaneous water use efficiency is defined as In this paper, we defined ecosystem water use, , A revisit of WUE e concept: Water use efficiency by RS community NCE Influence on R h : Hardwoods NCE Influence on R h : Red Pine There seems a strong correlation with stand age and ecosystem type! Whats next? Is (R a /ET) varying with age & disturbance? Is (R a /ET) varying with age & disturbance? WUE e in non-growing season equals to (R a /E)! WUE e in non-growing season equals to (R a /E)! How is Ra regulated by biomass (LAI), temperature, and moisture? How is Ra regulated by biomass (LAI), temperature, and moisture? How does (NPP*WUE/GPP) vary with time scale (i.e., hours-years)? How does (NPP*WUE/GPP) vary with time scale (i.e., hours-years)? How does (NPP*WUE/GPP) change with sucession and disturbance? How does (NPP*WUE/GPP) change with sucession and disturbance? Summary of growing season NEE for comparable pine ecosystems of various age classes. Data is from Baldocchi et al. 1997, Joiner et al. 1999, Pypker & Fredeen 2002, Griffis et al. 2003). Euskirchen et al. (in revision) Hypothesized carbon flux of forest ecosystems after a disturbance Questions?Support provided by the National Science Foundation, Southern Global Change Program, and WESTGEC of DOE