# Presentation: 108872

## Annual Mean Pattern of CO2 Flux

- NEE

- GEE

- RESP

- Mean CO2 Exchanges kgC ha d-1

- mmol m-2 d-1

- Month

- Nov

- Dec

- Jan

- Feb

- Mar

- Apr

- May

- Jun

- Jul

- Aug

- Sep

- Oct

- Annual Mean Pattern of CO2 Flux
- at Harvard Forest:1992-1999

- -100

- -50

- 0

- 50

- -800

- -600

- -400

- -200

- 0

- 200

- 400

- Elevated R after leaf drop and in spring when soils warm but canopy has not developed
- Gross uptake is apparent in early April, as soon as the site thaws, but there is not enough foliage in conifers and evergreen shrubs to offset the increased Soil Respiration
- Respiration continues over the entire winter, with a gradual decline after the sharp drop in Decmber (onset of freezing temperatures on average)

## Deviations From the Mean at Harvard Forest

- Deviation from mean TemperaturesOuter axes (C)

- Deviations From the Mean at Harvard Forest

- anomalous cold air tempbut deep snow allowedtypical soil temp

- 1992

- Tair

- Tsoil

- -10

- -5

- 0

- 5

- 10

- -100

- -50

- 0

- 50

- 100

- 150

- 1993

- -10

- -5

- 0

- 5

- 10

- -100

- -50

- 0

- 50

- 100

- 150

- 1994

- -10

- -5

- 0

- 5

- 10

- -100

- -50

- 0

- 50

- 100

- 150

- 1995

- nov

- dec

- jan

- feb

- mar

- apr

- may

- jun

- jul

- aug

- sep

- oct

- -10

- -5

- 0

- 5

- 10

- -100

- -50

- 0

- 50

- 100

- 150

- 1996

- -10

- -5

- 0

- 5

- 10

- 1997

- -10

- -5

- 0

- 5

- 10

- 1998

- -10

- -5

- 0

- 5

- 10

- 1999

- nov

- dec

- jan

- feb

- mar

- apr

- may

- jun

- jul

- aug

- sep

- oct

- -10

- -5

- 0

- 5

- 10

- Monthly Deviation from mean precipitationInner Axis (mm)

- Low Precip

## Deviations From the Mean at Harvard Forest

- 1992

- 1993

- 1994

- 1995

- nov

- dec

- jan

- feb

- mar

- apr

- may

- jun

- jul

- aug

- sep

- oct

- 1996

- -20

- -10

- 0

- 10

- 20

- 1997

- -20

- -10

- 0

- 10

- 20

- 1998

- -20

- -10

- 0

- 10

- 20

- 1999

- nov

- dec

- jan

- feb

- mar

- apr

- may

- jun

- jul

- aug

- sep

- oct

- -20

- -10

- 0

- 10

- 20

- Deviation from mean CO2 Flux  kg-C ha-1d-1

## Deviations From the Mean at Harvard Forest

- Deviation from mean NEE  kg-C ha-1d-1

- 1992

- -20

- -10

- 0

- 10

- 20

- 1993

- -20

- -10

- 0

- 10

- 20

- 1994

- -20

- -10

- 0

- 10

- 20

- 1995

- Nov

- Dec

- Jan

- Feb

- Mar

- Apr

- May

- Jun

- Jul

- Aug

- Sep

- Oct

- -20

- -10

- 0

- 10

- 20

- 1996

- -20

- -10

- 0

- 10

- 20

- 1997

- -20

- -10

- 0

- 10

- 20

- 1998

- -20

- -10

- 0

- 10

- 20

- 1999

- Nov

- Dec

- Jan

- Feb

- Mar

- Apr

- May

- Jun

- Jul

- Aug

- Sep

- Oct

- -20

- -10

- 0

- 10

- 20

- Normal NEE

## Deviations From the Mean at Harvard Forest

- Deviations From the Mean at Harvard Forest

- 1992

- -20

- -10

- 0

- 10

- 20

- 1993

- -20

- -10

- 0

- 10

- 20

- 1994

- -20

- -10

- 0

- 10

- 20

- 1995

- Nov

- Dec

- Jan

- Feb

- Mar

- Apr

- May

- Jun

- Jul

- Aug

- Sep

- Oct

- -20

- -10

- 0

- 10

- 20

- 1996

- -20

- -10

- 0

- 10

- 20

- 1997

- -20

- -10

- 0

- 10

- 20

- 1998

- -20

- -10

- 0

- 10

- 20

- 1999

- Nov

- Dec

- Jan

- Feb

- Mar

- Apr

- May

- Jun

- Jul

- Aug

- Sep

- Oct

- -20

- -10

- 0

- 10

- 20

- Increased GEE

## Deviations From the Mean at Harvard Forest

- 1992

- -20

- -10

- 0

- 10

- 20

- 1993

- -20

- -10

- 0

- 10

- 20

- 1994

- -20

- -10

- 0

- 10

- 20

- 1995

- nov

- dec

- jan

- feb

- mar

- apr

- may

- jun

- jul

- aug

- sep

- oct

- -20

- -10

- 0

- 10

- 20

- 1996

- -20

- -10

- 0

- 10

- 20

- 1997

- -20

- -10

- 0

- 10

- 20

- 1998

- -20

- -10

- 0

- 10

- 20

- 1999

- nov

- dec

- jan

- feb

- mar

- apr

- may

- jun

- jul

- aug

- sep

- oct

- -20

- -10

- 0

- 10

- 20

- Deviation from mean Respiration kg-C ha-1d-1

- Deviations From the Mean at Harvard Forest

- Reduced R

- Increased Raftertropical storm and autumn rains

## Parameters {ai,m} estimated using Model-0 (see Eq. 1).  Panel A  a1 versus month of year (units of mmoles CO2 m-2 s-1).  Parameter a1 is the monthly ecosystem respiration rate at the monthly mean temperature, Tmean.  Panel B  a2 versus month of year (units of mmoles CO2  m-2 deg-1 s-1). Parameter a2 is the short term ecosystem respiration response to temperature.  Panel C  a3 versus month of year (units of mmoles CO2 m-2 s-1). Parameter a3 is the ecosystem maximum CO2 assimilation rate.  Panel D  -a3/a4 versus month of year (units of mmoles CO2 m-2 mE-1 s-1).  The ratio -a3/a4 represents the canopy photosynthesis quantum yield. 

- Parameters {ai,m} estimated using *Model-0* (see Eq. 1).  **Panel A**  a1 versus month of year (units of mmoles CO2 m-2 s-1).  Parameter a1 is the monthly ecosystem respiration rate at the monthly mean temperature, Tmean.  **Panel B**  a2 versus month of year (units of mmoles CO2  m-2 deg-1 s-1). Parameter a2 is the short term ecosystem respiration response to temperature.  **Panel C**  a3 versus month of year (units of mmoles CO2 m-2 s-1). Parameter a3 is the ecosystem maximum CO2 assimilation rate.  **Panel D**  -a3/a4 versus month of year (units of mmoles CO2 m-2 mE-1 s-1).  The ratio -a3/a4 represents the canopy photosynthesis quantum yield.

## Five day aggregates of hourly observed (black line) and  Model-0 predicted (orange line) CO2 flux (units of mmoles CO2 m-2 s-1) for the month of August  (1992-1999)

## Five day aggregates of hourly observed (black line) and  Model-0 predicted (blue and orange lines) CO2 flux (units of mmoles CO2 m-2 s-1) for the month of May (1992 -1999). The orange (blue) line is the Model-0 predicted CO2 flux without (with) phenology index (see text and Eq. 1a).

## Effects of aggregation time on Model-0 predictions.  R2 of Model-0 predicted NEE for hourly, daily, and monthly aggregation of the data,  by season.  Summer= June, July, August; Winter=December, January, February (blue diamonds;  summer with soil moisture correction (red crosses), Model-0.5.  

## Slide 11

## Stable measurements  and long-term calibrations are essential for analysis of deviations from mean patterns 

- Note that NEE is the difference between large GEE and Reco terms.
- The characteristic times for GEE and Reco are not the same: Current rates may be relicts of conditions in previous seasons/years.
- GEE depends on current temperature and light, biomass, and events at bud set and bud-break
- Reco depends on temperature and moisture, and the magnitude of litter pools.

**Considerations for analysis of interannual variations in CO****2**** fluxes.**

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