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Carbon & Water Exchange of California Rangelands: A n Oak-Grass Savanna, Annual Grassland and Peatland Pasture Ecosystem. Dennis Baldocchi Biometeorology Lab, ESPM University of California, Berkeley. Scientific and Management Questions.

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Carbon & Water Exchange of California Rangelands:An Oak-Grass Savanna, Annual Grassland and Peatland Pasture Ecosystem

Dennis Baldocchi

Biometeorology Lab, ESPM

University of California, Berkeley

Scientific and management questions
Scientific and Management Questions

  • What are the magnitudes and temporal variability of the exchanges of energy, CO2 and water vapor in terrestrial ecosystems?

    • Is my rangeland a Carbon Sink?

    • If, not, How can I manage it to become one?

  • How does climate, vegetation type, physiological conditions phenology, changes in land use, management and disturbance history modulate the exchange of energy, carbon and water; and vice versa?

    • Can my rangeland off-set global warming?

    • Can it conserve water for the watershed and reservoir?

Take home messages
Take Home Messages

  • Oak Woodlands are modest Carbon Sinks, Grasslands are Carbon Neutral, & Peatlandpastures are Carbon Sources

  • Year-to-year variability in Carbon Uptake is due to length of the wet season.

    • Oaks are risk adverse and experience less inter-annual variability in NEE than grasslands

  • Savanna woodlands use/need more water than annual grasslands

    • Trees tap ground-water to sustain themselves during the summer

  • Oak woodlands are darker and warmer than annual grasslands


TonziRanch Flux Tower

Annual Grassland


Oak grass savanna a two layer system
Oak-Grass Savanna: A Two Layer System


Trees deciduous; grass green


Trees green; grass dead


Trees green;grass green

Oak grass savanna are model systems for studying ecosystem ecology
Oak-Grass Savanna are Model Systems for Studying Ecosystem Ecology

  • Structure/Function

    • Oak and grasses provide contrasting life forms, woody/herbaceous, perennial/annual

    • The Canopy is open and heterogeneous

      • gives us a opportunity to test the applicability of ecosystem and biogeophysical models, developed for ideal and closed canopies

  • Environmental Biology

    • The Mediterranean climate provides distinct wet/ cool and dry/hot seasons to examine the ecosystem response (photosynthesis, transpiration, respiration, stomatal conductance) to a spectrum of soil moisture and temperature conditions

  • Global Change

    • The Mediterranean climate experiences great extremes in inter-annual variability in rainfall; we experience a wider range in precipitation over a few years than long-term predicted changes.

Sherman Island Peatland Pasture

Peatland Pastures are a Model for studying Land Subsidence and Carbon Management in the Delta

Background Conditions

Annual precipitation 500 700 mm y mean annual temperature 14 16 c
Annual Precipitation ~500 - 700 mm/yMean Annual Temperature ~ 14-16 C

Climate trends pardee ca
Climate Trends: Pardee, CA

Temperature Increased by about 1.25 C over 50 Years;

Precipitation Trend is Flat, but with High Inter-annual Variation

Environmental Conditions

Ma et al, in prep

Experimental methods
Experimental Methods

  • Eddy Covariance

    • above the stand (20 m tower)

    • below the stand (2 m tower)

  • Micrometeorology

  • Sap flow (heat pulse)

  • Soil respiration chambers

  • Leaf Physiology (A-Ci curves)

Results and discussion
Results and Discussion

Pasture is a Carbon Source


NEE = +27 gC m-2 y-1, 2008

NEE = +82 gC m-2 y-1, April, 2007-April ,2008

Oak Woodlands are Carbon Sinks, -92 +/- 43 gC m-2 y-1

Annual Grasslands are Carbon Neutral, 30 +/- 116 gC m-2 y-1

Oak Woodlands are Risk Adverse, they Experience less inter-annual variation in NEE than Grasslands


16.86 sheets of 8 ½ by 11 inch paper is 1 m2 in area and equals 76 g

Carbon Fluxes Scales with Spring Rainfall

Ma et al, 2007 AgForMet

Net Primary Productivity

John Battle's biometric NPP = 235 gC m-2 y-1.

NPP = GPPtree - Ra_tree - Rh = 299 gC m-2 y-1

NPP=NEP+Rh=97+186=283 gC m-2 y-1.

Interannual Variability in

GPP and Reco scale with one


Sustained and Elevated Rates of Respiration after Fall Rain

Impacts of photosynthesis and rain pulse on ecosystem respiration of the oak woodland
Impacts of Photosynthesis and rain pulse on ecosystem respiration of the Oak Woodland

Baldocchi et al, JGR, Biogeosciences, 2006

Remote Sensing of respiration of the Oak WoodlandCanopy Structure and NPP

Ikonos 1 m resolution in b w 4 m res in color
IKONOS: respiration of the Oak Woodland1 m resolution in b/w; 4 m res. in color

Lidar measurement of tree height
LIDAR Measurement of Tree Height respiration of the Oak Woodland

Upscale GPP and NEE to the Biome Scale respiration of the Oak Woodland

area-averaged fluxes of NEE and GPP were -150 and 932 gC m-2 y-1

net and gross carbon fluxes equal -8.6 and 53.8 TgC y-1

Jingfeng Xiao and D Baldocchi

Water, Energy respiration of the Oak Woodlandand Evaporation

Evaporation from Irrigated Pasture respiration of the Oak Woodland

Inter-annual Variation in Rain and Evaporation respiration of the Oak Woodland

On Average, Woodland Uses 410 mm of Water on 540 mm of Rain

Oak Trees respiration of the Oak WoodlandTap Ground Water, and Must to Survive

G. Miller, Y. Rubin, D. Baldocchi unpublished data

Oak Trees Access a Significant Fraction of Water from Water Table

G. Miller, Y. Rubin, S. Ma, D. Baldocchi unpublished data

Role of Land Management on Table

Water and Energy Exchange and Climate

Case Study:

Savanna Woodland vs Grassland

Oak Woodlands are Warmer than Grasslands Table

Mean Potential Temperature difference Equals 0.84 C;

grass: 290.72 K vs savanna: 291.56 K

Available Energy Drives Heat Exchange and Evaporation Table

  • Savanna absorbs much more Radiation (3.18 GJ m-2 y-1) than

  • the Grassland (2.28 GJ m-2 y-1) ; DRn: 28.4 W m-2

Savanna Tableinjects more Sensible Heat into the atmosphere because it has more Available Energy and it is Aerodynamically Rougher

Tall and Rougher Savanna Promotes Turbulent mixing over Short, SmootherGrassland

Landscape TableDifferences on Short Time Scales:

Grass ET > Forest ET

Role of Land Use on TableET on Annual Time Scales:

Annual Oak ET (400 +/-35 mm/y) > Grass ET (322 +/-48 mm/y)

Conclusions Table

  • Oak Woodlands are Carbon Sinks, Grasslands are Carbon Neutral

  • Year to year variability in Carbon Uptake is due to length of wet season.

    • Oaks are risk adverse and experience less inter-annual variability in NEE than grasslands

  • Photosynthesis and Respiration are tightly linked

    • Oaks need high N levels to attain sufficient rates of carbon assimilation for the short growing season

  • Savanna woodlands need about 80 mm more water to function than nearby grasslands

    • Trees tap ground-water to sustain themselves during the summer

  • Oaks are darker and warmer than grasslands

Biometeorology team
Biometeorology Team Table

Funding: US DOE/TCP; NASA;

WESTGEC; Kearney; Ca Ag Expt Station

Questions Table

  • How would you use these data to make land mgt Decisions?

    • Are you compelled to cut-trees for grass, to save water and cool the climate?

      • What about Topography and the role of trees to maintain soils and serve as habitat

    • Encourage trees on grasslands to sequester carbon?

      • Do you have enough rain?

    • Should Delta Peatland Pastures revert back to tules and wetlands?

      • What about methane emissions (20x CO2), mosquitoes and water quality?

Annual et and interannual variation
Annual ET and Interannual Variation Table

Savanna Soil Stores about 80 mm water and uses that much extra to sustain a sparse woodland, over a grassland

Canopy structure laser altimeter data
Canopy Structure: TableLaser Altimeter Data

Goals of research
Goals of Research Table

  • Quantify the Biophysical Controls on Ecosystem Metabolism (carbon gains and losses) and Water Balance of Oak Woodlands and Peatland Pastures

  • Quantify and understand mechanisms controlling net annual budgets and inter-annual variability of carbon, water and energy exchange of oak woodland and annual grassland and Peatland Pastures

  • Produce predictive and mechanistic ability to quantify future conditions, e.g. global warming, elevated CO2 and ozone, perturbed water supply, and land use change, land subsidence, methane emissions and in order to manage rangelands

  • Upscale fluxes to the region for management decisions

Kueppers et al 2005 PNAS

Sherman Island TablePeatland Pasture

Evidence of Trees Tapping Ground Water Table

G. Miller 2009, PhD Dissertation

ET and Soil Water Deficits: Table

Root-Weighted Soil Moisture

Baldocchi et al., 2004 AgForMet

Dynamics of grassland canopy structure
Dynamics of TableGrassland Canopy Structure