Modeling Modes of Variability in Carbon Exchange Between High Latitude Ecosystems and the Atmosphere Dave McGuire (UAF), Joy Clein (UAF), and Qianlai Zhuang (MBL) Map Courtesy of Cath Copass

Organization of Talk Why is understanding carbon exchange of high latitude ecosystems important? Progress in modeling: - seasonal-scale exchange - interannual-scale exchange - decadal-scale exchange - century-scale exchange Summary

Feedbacks of Terrestrial Ecosystems to the Earth’s Climate System Regional ClimateGlobal Climate Terrestrial Ecosystems Impacts Water and energy exchange Exchange of radiatively active gases (CO 2 and CH 4 ) Delivery of freshwater to Arctic Ocean

Strategy to Evaluate Seasonal Exchange of Carbon Simulated by Terrestrial Biosphere Models

Terrestrial models underestimate winter CO 2 concentrations and drawdown CO 2 too early in the spring (from Dargaville et al., 2002)

Seasonal Variability Winter Exchange - Does underestimate of atmospheric CO 2 concentrations in winter indicate that terrestrial ecosystem models should do a better job in representing controls over winter decomposition? Exchange at transition from winter to summer - Does early drawdown of atmospheric CO 2 at the winter to summer transition indicate that terrestrial ecosystem should do a better job in representing consideration the effects of spring thaw on carbon exchange?

(from McGuire et al., 2000)

(Running et al., EOS)

Coupling STM to TEM Vegetation type;Snow pack; Soil moisture Soil temperature TEM STM

Mean Net Carbon Exchange during the 1980s (Zhuang et al., 2003)

Comparison of Observed and Simulated CO 2 at Monitoring Stations (from Zhuang et al., 2003)

Inter-annual Variability Climate - To what extent does variability in temperature, precipitation, and radiation influence inter-annual variability in carbon exchange? Disturbance - To what extent does variability in climate vs. disturbance influence inter-annual variability in carbon exchange?

(Positive Values Indicate Carbon Release, Negative Values Indicate Carbon Storage)

Application of STM-TEM parameterized for black spruce at Taiga LTER to simulate the C fluxes of the NSA-OBS BOREAS site. Field-based estimates are based on eddy covariance measurements. Zhuang et al

(from McGuire et al., in preparation)

CO 2 Concentration Climate (Temperature, Precipitation) STM-TEM Carbon Pools NPP R H NCE Fire Emissions Fire regime (Severity, History)

Uptake Release GAC 7/29/02 Rates weighted by area

Stations used to constrain atmospheric inversions of high latitudes

Alaska and Canada Carbon Flux Variability from an Atmospheric Inversion - R. Dargaville Comparison of process-based and atmospheric approaches for Alaska-Canada after consideration of fire by the process-based approach (from McGuire et al., In preparation)

Decadal Variability Climate To what extent do changes in the start and length of the growing season influence decadal changes in carbon storage? (Zhuang et al., 2003) Disturbance Can responses of carbon exchange to changes in disturbance regime negate carbon storage that might be gained from longer growing seasons? (McGuire et al., in press).

Courtesy of K. McDonald

Biomass of Northern Hemisphere Ecosystems has been Changing in Recent Decades From Myneni et al. (2001)

(Fire in Canada became more frequent after 1970)

Cumulative Changes in Carbon Stocks for Canada from (from McGuire et al., in press)

Century-Scale Variability Will changes in vegetation distribution dominate? (McGuire and Hobbie, 1997) Will directional changes in disturbance regimes dominate? (Kurz and Apps, 1999; McGuire et al., in press) How sensitive is the response of carbon storage to how fast carbon cycles through soils? (Clein et al., 2000)

Soil carbon storage depends on the dynamics of carbon and nitrogen transformations in soils. From Clein et al. (2000)

TEM, reference TEM, fast soil C Different representations of soil carbon transformations have different impacts on century-scale responses of carbon storage. (from Clein et al., 2000)

Summary Seasonal variation improved by representing insulating effects of snowpack on winter decomposition and representing freeze-thaw processes. Inter-annual responses to climate not well understood at large scales. At local scales responses depend on soil moisture. Need to more accurately represent hydrologic variability across the landscape. It is not clear whether improvement of decadal responses requires improved information on winter precipitation or requires improved snowmelt algorithms in models. Century-scale responses may be improved through better understanding of carbon and nitrogen transformations in soils. Disturbance can have strong effects on carbon storage at all time scales.