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Michael Gavazzi 1 , Asko Noormets 2 , Steve G. McNulty 1 , Ge Sun 1 , Jean-Christophe Domec 2 ,

Figure 1. Ecosystem provinces of US (Bailey et al., 1994), and Soil carbon stocks in SE-US (Johnson & Kern (2003). Carbon Pools and Fluxes in a Coastal Plain Loblolly Pine Plantation. Michael Gavazzi 1 , Asko Noormets 2 , Steve G. McNulty 1 , Ge Sun 1 , Jean-Christophe Domec 2 ,

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Michael Gavazzi 1 , Asko Noormets 2 , Steve G. McNulty 1 , Ge Sun 1 , Jean-Christophe Domec 2 ,

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  1. Figure 1. Ecosystem provinces of US (Bailey et al., 1994), and Soil carbon stocks in SE-US (Johnson & Kern (2003). Carbon Pools and Fluxes in a Coastal Plain Loblolly Pine Plantation Michael Gavazzi1, Asko Noormets2, Steve G. McNulty1, Ge Sun1, Jean-Christophe Domec2, John S. King2, Jiquan Chen3, Emrys Treasure1 1USDA FS Southern Global Change Program, 2North Carolina State University, 3University of Toledo Soil carbon flux Effect of drought Introduction Coastal plain ecosystems comprise only about 5% of total U.S. land area, but the soil carbon density in these ecosystems is about 10-fold higher than in upland ecosystems and they may play a disproportionately large role in ecosystem-climate feedbacks. The role of these ecosystems in continental carbon exchange is largely unclear because they have been underrepresented in flux monitoring networks. We monitored ecosystem carbon fluxes and pools for three years in two lower coastal plain loblolly pine plantations (3 and 17 years of age in 2007). The contribution of soil to ecosystem respiration decreased from over 90% immediately following a harvest to about 55-60% by age 17. The replenishment of soil C through litterfall in the 17-yr old stand equaled heterotrophic respiration (Rh) in 2006, but was 7 and 30% lower than Rh in 2007 and 2005, highlighting the sensitivity of soil carbon stocks to interannual climate variability. Throughout three years, the net loss of soil C was 233 g m-2. Figure 4. Forest floor at the 17-yr old loblolly pine plantation in the lower coastal plain of NC, USA. Figure 6. The seasonal dynamics of canopy conductance (gc) and tree hydraulic conductance in the 17-yr old stand. Table 2. Annual carbon fluxes (g C m-2 yr-1) in the 3- and 17-year old Loblolly pine plantations in the lower coastal plain in North Carolina. Figure 5. The annual course of micrometeorological parameters at the 17-yr old loblolly pine plantation during three years. Table 3. The balance between litterfall and heterotrophic respiration (both in g C m-2 yr-1) in the 17-yr old loblolly pine stand. Figure 2. The effect of coarse woody debris on forest net carbon balance and soil respiration. The error bars represent gapfilling uncertainty for net ecosystem exchange of CO2 (NEE), and standard deviation for coarse woody matter (CWM) and soil respiration (SR). Summary – Soil carbon flux Even a conservatively estimated ratio of Rh:SR of 0.5 indicates that losses of soil carbon exceed new inputs through litter at the 17-yr old stand. The average loss of 79 g C m-2 yr-1 is higher than the average from all non-permafrost peatlands in the conterminous US (60 g C m-2 yr-1; Bridgham et al., 2006). Figure 7. Monthly mean canopy conductance as a function of cumulative precipitation deficit (a) and monthly NEE as a function of canopy conductance (b). Figure 8. Precipitation use efficiency (PUE) as a function of annual precipitation, expressed on the basis of GEP (a) and NEE (b). Carbon pools and fluxes Summary - Effect of drought The interannual differences in precipitation (nearly 700 mm) had limited effects on both GEP and ER, even though canopy conductance and tree hydraulic conductance were suppressed by low soil moisture. Although respiration was slightly limited by low moisture, this effect was overridden by stimulation by higher temperature. Consequently, the small effects on GEP and ER compounded so that the decrease in NEE-based precipitation use efficiency was significantly greater than on GEP basis. Selected References Amiro BD, Chen JM, Liu J (2000) Can J For Res 30:939-947. Bailey RG (1995) USDA Forest Service, pp. 108. Berbigier P, Bonnefond J-M, Mellmann P (2001) Agric For Meteorol 108:183-197. Bridgham SD, Megonigal JP, Keller JK, Bliss NB, Trettin CC (2006) Wetlands 26:889-916. Clark KL, Gholz HL, Moncrieff JB, Cropley F, Loescher HW (1999) Ecol Appl 9:936-948. Law BE, Sun OJ, Campbell J, Van Tuyl S, Thornton PE (2003) Global Change Biol 9:510-524. Noormets A, Chen J, Crow TR (2007) Ecosystems 10:187-203. Figure 3. Age-related changes in forest net carbon balance at different latitudes. Summary - Carbon pools and fluxes The CO2 exchange rates are high at the two studied coastal plain loblolly pine plantations, rivaling those in tropical forests, but similar to other commercially managed pine plantations (Clark et al. 1999; Berbigier et al. 2001). Post-disturbance C losses from logging residue and soil are substantial, but the source period appears to be shorter than reported for more northern forests (Amiro et al. 2000; Law et al. 2003; Noormets et al. 2007). Acknowledgements This research is funded in part by NASA Grant NRA-04-OES-01 and the USDA Forest Service Northern Global Change Program Table 1. Carbon pools (mean ± 95%CI; Mg C ha-1) in the 17-yr old loblolly pine stand. Abbreviations: AGB – aboveground, BGB – belowground, USB – understory biomass, and CWM – coarse woody material.

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