INTRODUCTION, OBJECTIVES AND SCOPE

IN 1998, INTERNATIONAL AND SPACE AGENCIES INTERESTED IN SYSTEMATIC GLOBAL OBSERVATIONS ESTABLISHED THE INTEGRATED GLOBAL OBSERVING STRATEGY PARTNERSHIP, IGOS-P (www.igospartners.org). IGOS-P has developed 'Observation themes' each consisting of a set of related observations required to deal with a particular aspect of the Earth system. The definition of these themes is carried out in collaboration with relevant international programmes and groups.

In response to growing interest in terrestrial carbon the IGOS-P requested that the Global Terrestrial Observing System (GTOS) prepare a proposal for a Terrestrial Carbon Observation (TCO) theme. After circulation in the international scientific and policy communities a revised TCO proposal (TOPC, 1999) was submitted to IGOS-P at its annual meeting in November, 1999 where the following decisions were made:

Action 4/5 - GTOS, with the Food and Agriculture Organization (FAO) support, to lead the Terrestrial Carbon Cycle (TCC) theme and present a report to the Partners along the lines of the Oceans theme report.
Action 4/6 - Global Climate Observing System (GCOS), FAO, International Geosphere-Biosphere Programme (IGBP), International Council for Scientific Unions (ICSU), United Nations Educational, Scientific and Cultural Organization (UNESCO), and the Committee on Earth Observation Satellites (CEOS) to nominate representatives for the Terrestrial Carbon Cycle team by the end of November 1999.
Action 4/9 - The Global Ocean Observing System (GOOS), GCOS, GTOS, IGBP, and the National Aeronautics and Space Administration (NASA) to prepare proposals for the overarching Global Carbon Theme and to decide amongst themselves who should lead this activity.

To develop the terrestrial carbon observation theme, a Theme Team was established. This team has participated in a series of activities that include:

the completion of a synthesis workshop in February 2000 (FAO, 2002b);
the definition and review of observation requirements through two scientific meetings organized by IGBP (in June and October 2000);
the preparation of a draft TCO theme report for the annual IGOS-P meeting in November 2000;
and the completion of the final version of the TCO report in February 2001 (FAO, 2002a).

Information on TCO can be found at: www.fao.org/gtos/TCO.html

The TCO observation concept is based on a 'top-down' and 'bottom-up' approach, supported by satellite and in situ observations and by a range of models of key environmental components (atmosphere, vegetation, soils and their interactions) involved in the terrestrial component of the carbon cycle.

During the preparation of the theme report it became evident that the in situ component is more complex and much less organized at the global level than the satellite component. To accelerate the preparations for TCO implementation, GTOS with IGBP decided to hold a workshop specifically addressing in situ data issues. The meeting was held on 5-8 June 2001 in Frascati, Italy with local support provided by FAO and the GTOS Secretariat. The objectives of the workshop were to:

1. assess the capacity and readiness of existing key in situ observation and analysis components for a TCO system;
2. analyse the comprehensiveness of geographic (continents, regions) and thematic (input data to information outputs) coverage of existing components;
3. identify gaps and discuss possible approaches to filling these gaps to meet TCO requirements;
4. assess the feasibility of, and steps involved in, the preparation of in situ data sets needed to complement satellite observations;
5. prepare a meeting report containing the elements for a provisional in situ TCO implementation plan.

For this workshop, in situ data/products were broadly defined as data or products obtained through non-remote sensing means (i.e. ground measurements). The exceptions are resource inventories (e.g. forest) that are often produced through air photo interpretation with variable field sampling, and trace gas composition measurements that can be made on towers or from aircraft as well as at the surface.

The participants represented programmes that are global, continental, regional, or national in scope and are concerned with carbon-related observations. The following sections of this report summarize the priority actions identified by the participants:

Chapter 2

actions to move TCO forward;

Chapter 3

general review of in situ data and their roles in TCO;

Chapter 4

point in situ data and products;

Chapter 5

gridded in situ data and products;

Chapter 6

data and information management;

Appendix III

detailed information on national carbon related data sets;

Appendix IV

details on other terrestrial carbon data acquisition programmes, networks, and data products.

Table 1 summaries the major issues of TCO in situ data sets. Further details can be found in the section on Specific data needs (page 16).

The major goals for TCO are:

1. by 2005, demonstrate the capability to estimate annual net land-atmosphere fluxes at a sub-continental scale (107 km2) with an accuracy of +/- 30% globally, and at a regional scale (106 km2) over areas selected for specific campaigns with similar or better accuracy;

2. by 2008, improve the performance to better spatial resolution (106 km2 globally) and an increased accuracy (+/- 20%);

3. In each case, produce flux emission estimate maps with the highest spatial resolution enabled by the available satellite-derived and other input products.

Meeting these goals will also generate early valuable results, and serve as a mechanism for the further evolution of TCO. A design team has been established by GTOS to prepare an implementation plan. TCO will rely on the collaboration of agencies, programmes, and projects that share interest in the terrestrial carbon cycle. Current and planned regional studies (the Amazon, in Europe, North America, Siberia, etc.) will be important for the progress of TCO. The design team is also collaborating in the preparation of the Integrated Global Carbon Observation (IGCO) theme to ensure the integration of terrestrial, atmospheric, and ocean components.

Table 1. Observation requirements for bottom-up approach*

Variable

Type (a)

Spatial (b)

Temporal (c)

Method (d)

Comments

1. DRIVING VARIABLES, GRIDDED (for model application/upscaling, required at every grid point)

ATMOSPHERE

Air temperature

1

3

1,6

1,2,3

daily maximum, minimum, mean

Precipitation

1

3

1,6

1,2,3

Photosynthetically active radiation

1

3

1,6

1,2,3

Relative humidity

1

3

1,6

1,2,3

Wind speed

1

3

1,6

1,2,3

Net radiation

1

3

1,6

1,2,3

Snow water equivalent

1

3

1,6

1,2,3

Aerosols

1

3

1,6

1,2,3

for atmospheric corrections of optical data

Integrated atmospheric water vapour

1

1

6

1,2,3

for atmospheric corrections of optical data

ECOSYSTEM

Vegetation cover class

2

1

4

3

physiognomic classes, dominant species

Biota biomass

2

1

4

3

may be used to drive decomposition models

Soil moisture

3

1

1

2,3

Leaf area index

2

1

4

3

Foliage nitrogen

2

1

4

3

needed to drive decomposition rates

Chlorophyll

2

1

4

3

to drive canopy photosynthesis in some models

Natural disturbance history

1,2

1

4

1,4

includes biomass burning and insect-induced mortality

Management history

1,2

1

4

4

includes forest harvest, thinning, fertilization, etc.

Topography

2

1

3

3, 4

influences radiation and surface water

2. CALIBRATION/VALIDATION VARIABLES, POINT (required at selected sites)

ATMOSPHERE

Air temperature

1

2

6

1

15 to 60 minute averages (continuous)

Precipitation

1

2

6

1

15 to 60 minute averages (continuous)

Solar radiation

1

2

6

1

15 to 60 minute averages (continuous)

Relative humidity

1

2

6

1

15 to 60 minute averages (continuous)

Wind speed

1

2

6

1

15 to 60 minute averages (continuous)

Net radiation

1

2

6

1

15 to 60 minute averages (continuous)

CO₂ concentration profile

1

2

6

1

15 to 60 minute averages (continuous)

Integrated atmospheric water vapour

1

2

6

1

for atmospheric corrections of optical data

Snow water equivalent

1

2

1,6

1

15 to 60 minute averages (continuous)

Aerosols

1

2

1,6

1

15 to 60 minute averages (continuous; for atmospheric corrections)

ECOSYSTEM

SITE

Natural disturbance history

1,2

2

4

1,4

includes fires and insect-induced mortality

Management history

1,2

2

4

4

includes harvest, thinning, fertilization, etc.

Topography

2

2

3

3, 4

influences radiation, and water fields

Spatial pattern

2

1,2

3

3, 4

may assist spatial scaling

VEGETATION

Vegetation cover class

2

2

2

1

physiognomic classes, dominant species

Root carbon

2

2

2

1

coarse and fine

Above-ground biomass

2

2

2

1

stem, branch, foliage

Leaf area index

2

2

4

1

Foliage nitrogen

2

2

4

1

used for canopy photosynthesis modelling

SOIL

Biota carbon and nitrogen

2

2

4

1

may be used to drive decomposition models

Biota biomass

2

2

4

1

may be used to drive decomposition models

Temperature profile

1,2

2

4

1,2

profiles are useful as a driver and for process studies

Maximum thaw depth

1,2

2

4

1,2

critical for climate impact on permafrost-affected areas

Thermal conductance

2

2

3

1, 2

to estimate heat transfer and heterotrophic respiration

Thermal diffusivity

2

2

3

1, 2

related to thermal conductance but needs heat capacity information

Soil moisture

1,2

2

5

1, 2

affects heat transfer and decomposition

Hydraulic properties

2

2

3

1, 2

for vertical and horizontal water exchange

Ground water table depth

2

1,2

4,5

1,2

influences wetland dynamics

Carbon content (organic & inorganic)

2

2

3

1

directly affects heterotrophic respiration

Carbon age

2

2

3

1

needed to improve Rh calculation

Nitrogen and phosphorus content

2

2

3

1

affects gross primary productivity

Bulk density

2

2

3

1

needed for diffusivity estimation

Sand and clay fraction (percentage)

2

2

3

1

pH

2

2

3

1

important limitation to growth and soil biology

Macro & micro nutrients

2

2

3

1

these processes affect plant nutrient uptake

Microbial biomass

2

2

3

1

affects decomposition

PHYSIOLOGY

Foliage nitrogen

2

2

2

1

needed to drive decomposition rates

Foliage lignin

2

2

2

1

needed to drive decomposition rates

Chlorophyll

2

2

2

1

needed to drive canopy photosynthesis in some models

Rubisco

2

2

2

1

needed to drive canopy photosynthesis in some models

FLUXES

Carbon fluxes (above & near ground)

3

2

6

1

critical for model validation

Above-ground NPP

3

2

4

1

carbon storage flux

Below-ground NPP

3

2

4

1

carbon storage flux

Litterfall nitrogen, phosphorus

2

2

2

1

carbon flux to soil & litterfall nutrients and carbon

indicate nutrient availability

Hydrogen and ET (above stand)

3

2

6

1

important for carbon flux estimation

CH₄

3

2

6

1

important for wetlands

VOC

3

2

6

1

can be significant in total carbon budget

DOC

3

2

2

1

carbon exchange can affect stocks and processes

Heterotrophic respiration rate

3

2

4

1

needed to validate NPP and NEP components

DOC = dissolved organic carbon, VOC = volatile organic carbon

a: 1 = external forcing variable; 2 = internal status variable; 3 = output variable

b: 1 = gridded with a resolution of 1 km or better; 2 = one or more sites for each land cover class; 3 = gridded with a resolution of 0.5-1 degree or better

c: 1, since industrialisation with desirable frequency; 2, periodical measurement once every 5-10 years; 3, one-time measurement; 4: multiple-year continuous measurement; 5, daily in calibrations years; 6, continuous

d: 1 = site measurement (including characterisation of its spatial heterogeneity as appropriate); 2 = modelling; 3 = remote sensing; 4 = existing survey or inventory

* From: FAO, 2002b

Chapter 2	actions to move TCO forward;
Chapter 3	general review of in situ data and their roles in TCO;
Chapter 4	point in situ data and products;
Chapter 5	gridded in situ data and products;
Chapter 6	data and information management;
Appendix III	detailed information on national carbon related data sets;
Appendix IV	details on other terrestrial carbon data acquisition programmes, networks, and data products.

Variable	Type (a)	Spatial (b)	Temporal (c)	Method (d)	Comments
1. DRIVING VARIABLES, GRIDDED (for model application/upscaling, required at every grid point)
*ATMOSPHERE*
Air temperature	1	3	1,6	1,2,3	daily maximum, minimum, mean
Precipitation	1	3	1,6	1,2,3
Photosynthetically active radiation	1	3	1,6	1,2,3
Relative humidity	1	3	1,6	1,2,3
Wind speed	1	3	1,6	1,2,3
Net radiation	1	3	1,6	1,2,3
Snow water equivalent	1	3	1,6	1,2,3
Aerosols	1	3	1,6	1,2,3	for atmospheric corrections of optical data
Integrated atmospheric water vapour	1	1	6	1,2,3	for atmospheric corrections of optical data
*ECOSYSTEM*
Vegetation cover class	2	1	4	3	physiognomic classes, dominant species
Biota biomass	2	1	4	3	may be used to drive decomposition models
Soil moisture	3	1	1	2,3
Leaf area index	2	1	4	3
Foliage nitrogen	2	1	4	3	needed to drive decomposition rates
Chlorophyll	2	1	4	3	to drive canopy photosynthesis in some models
Natural disturbance history	1,2	1	4	1,4	includes biomass burning and insect-induced mortality
Management history	1,2	1	4	4	includes forest harvest, thinning, fertilization, etc.
Topography	2	1	3	3, 4	influences radiation and surface water
2. CALIBRATION/VALIDATION VARIABLES, POINT (required at selected sites)
*ATMOSPHERE*
Air temperature	1	2	6	1	15 to 60 minute averages (continuous)
Precipitation	1	2	6	1	15 to 60 minute averages (continuous)
Solar radiation	1	2	6	1	15 to 60 minute averages (continuous)
Relative humidity	1	2	6	1	15 to 60 minute averages (continuous)
Wind speed	1	2	6	1	15 to 60 minute averages (continuous)
Net radiation	1	2	6	1	15 to 60 minute averages (continuous)
CO₂ concentration profile	1	2	6	1	15 to 60 minute averages (continuous)
Integrated atmospheric water vapour	1	2	6	1	for atmospheric corrections of optical data
Snow water equivalent	1	2	1,6	1	15 to 60 minute averages (continuous)
Aerosols	1	2	1,6	1	15 to 60 minute averages (continuous; for atmospheric corrections)
*ECOSYSTEM*
SITE
Natural disturbance history	1,2	2	4	1,4	includes fires and insect-induced mortality
Management history	1,2	2	4	4	includes harvest, thinning, fertilization, etc.
Topography	2	2	3	3, 4	influences radiation, and water fields
Spatial pattern	2	1,2	3	3, 4	may assist spatial scaling
VEGETATION
Vegetation cover class	2	2	2	1	physiognomic classes, dominant species
Root carbon	2	2	2	1	coarse and fine
Above-ground biomass	2	2	2	1	stem, branch, foliage
Leaf area index	2	2	4	1
Foliage nitrogen	2	2	4	1	used for canopy photosynthesis modelling
SOIL
Biota carbon and nitrogen	2	2	4	1	may be used to drive decomposition models
Biota biomass	2	2	4	1	may be used to drive decomposition models
Temperature profile	1,2	2	4	1,2	profiles are useful as a driver and for process studies
Maximum thaw depth	1,2	2	4	1,2	critical for climate impact on permafrost-affected areas
Thermal conductance	2	2	3	1, 2	to estimate heat transfer and heterotrophic respiration
Thermal diffusivity	2	2	3	1, 2	related to thermal conductance but needs heat capacity information
Soil moisture	1,2	2	5	1, 2	affects heat transfer and decomposition
Hydraulic properties	2	2	3	1, 2	for vertical and horizontal water exchange
Ground water table depth	2	1,2	4,5	1,2	influences wetland dynamics
Carbon content (organic & inorganic)	2	2	3	1	directly affects heterotrophic respiration
Carbon age	2	2	3	1	needed to improve Rh calculation
Nitrogen and phosphorus content	2	2	3	1	affects gross primary productivity
Bulk density	2	2	3	1	needed for diffusivity estimation
Sand and clay fraction (percentage)	2	2	3	1
pH	2	2	3	1	important limitation to growth and soil biology
Macro & micro nutrients	2	2	3	1	these processes affect plant nutrient uptake
Microbial biomass	2	2	3	1	affects decomposition
PHYSIOLOGY
Foliage nitrogen	2	2	2	1	needed to drive decomposition rates
Foliage lignin	2	2	2	1	needed to drive decomposition rates
Chlorophyll	2	2	2	1	needed to drive canopy photosynthesis in some models
Rubisco	2	2	2	1	needed to drive canopy photosynthesis in some models
FLUXES
Carbon fluxes (above & near ground)	3	2	6	1	critical for model validation
Above-ground NPP	3	2	4	1	carbon storage flux
Below-ground NPP	3	2	4	1	carbon storage flux
Litterfall nitrogen, phosphorus	2	2	2	1	carbon flux to soil & litterfall nutrients and carbon
indicate nutrient availability
Hydrogen and ET (above stand)	3	2	6	1	important for carbon flux estimation
CH₄	3	2	6	1	important for wetlands
VOC	3	2	6	1	can be significant in total carbon budget
DOC	3	2	2	1	carbon exchange can affect stocks and processes
Heterotrophic respiration rate	3	2	4	1	needed to validate NPP and NEP components
DOC = dissolved organic carbon, VOC = volatile organic carbon
a: 1 = external forcing variable; 2 = internal status variable; 3 = output variable
b: 1 = gridded with a resolution of 1 km or better; 2 = one or more sites for each land cover class; 3 = gridded with a resolution of 0.5-1 degree or better
c: 1, since industrialisation with desirable frequency; 2, periodical measurement once every 5-10 years; 3, one-time measurement; 4: multiple-year continuous measurement; 5, daily in calibrations years; 6, continuous
d: 1 = site measurement (including characterisation of its spatial heterogeneity as appropriate); 2 = modelling; 3 = remote sensing; 4 = existing survey or inventory