CO2 Fluxes across physiognomic types of neotropical savannas

Grace, J., Kruijt, B., Miranda, A.C., Miranda, H.S., Santos, A.J.B., DaSilva, G.T., Breyer, L. M., San José, J.J., Montes, R., Bracho, R., Nikonova, N., Mora, E., Castaldi, S., Cotrufo, G., and De Pasale, R.

Definition: Tropical seasonal ecosystems with a more or less continuous herbaceous layer and discontinuous cover of trees or shrubs in different proportions. (Frost, et al, 1986)

According to Bourliere and Hadley (1983) the term savanna designates a tropical grassland with scattered trees. Defined this way, savannas are the most common tropical landscape unit.

Global area, NPP, plant carbon content and soil carbon content in broadly categorized terrestrial ecosystems (Table 2 in Amthor, J.S. et al., 1998 - after Ajtay et al., 1979; Botkin and Simpson, 1990; Gorham, 1995; FAO, 1997)

Ecosystem Area NPP* NPP* Plant C Plant C Soil C Soil C Potential Potential (10^12 m^2) (gC/m^2/year) (Pg C/year) (g/m^2)* (Pg)* (g/m^2)& (Pg)& C gain rate C loss rate Forest, tropical 14.8 925 13.7 16500 244 8300 123 +++ ---Forest, temperate and plantation 7.5 670 5.0 12270 92 12000 90 ++ --Forest, Boreal 9.0 355 3.2 2445@ 22@ 15000 135 + ---Woodland, temperate 2.0 700 1.4 8000 16 12000 24 + -Chaparral 2.5 360 0.9 3200 8 12000 30 + -Savanna, tropical 22.5 790 17.7 2930 6 11700 264 ++++ ----Grassland, temperate 12.5 350 4.4 720 9 23600 295 +++ ----Tundra, arctic and alpine 9.5 105 1.0 630 6 12750 121 -----Desert and semidesert scrub 21.0 67 1.4 330 7 8000 168 + -Desert, extreme 9.0 11 0.1 35 0 2500 23 + -Perpetual ice 15.5 - - - - - - Lake and stream 2.0 200 0.4 10 0 - -Wetland 2.8 1180 3.3 4300 12 72000 202 +++ ---Peatland, northern 3.4 - - - - 133800 455 -----Cultivated and permanent crop 14.8 425 6.3 200 3 7900 117 + -Human area 2.0 100 0.2 500 1 5000 10 + - TOTAL 150.8 391 59.0 3220 486 13640 2057

Short- term site studies of one or two ecological aspects.

Different emphasis, like structure, determinants, nutrient cycles, biophysical properties, hydrology, energy balance, etc.

Due to the great heterogeneity of the savanna biome from site to site, and even from year to year, individual studies cannot provide a representative picture of the whole biome.

IGBP terrestrial transects

Kalahari transect

NATT ( North Australian Terrestrial Transect)

SALT (Savanna in long term)

The Miombo Network

SAFARI2000

SCOPE ( Tree-grass modeling group )

SAVAFLUX (EC, INCO-DC, South America)

SAVAFLUXFluxes of energy, water and carbon over disturbed

savanna ecosystems, and their application as indicators of sustainability and carbon

sequestration.Orinoco llanos

Cerrado

•Universidade de Brasília, Brazil •Instituto Venezolano de Investagaciones Cientificas, Venezuela•University of Edinburgh, UK •Seconda Universitá di Napoli, Italy

ScotlandItaly

SAVAFLUX QUESTIONS

1. What is the rate of carbon accumulation by savanna ecosystems?

2. How is this affected by disturbance?

3. Can fluxes be used as indicators of sustainability?

Objectives:

.- To establish a coherent picture of the pattern of variation in structure and biodiversity of savannas.

.- To link structure and biodiversity to function, by measuring and modelling the fluxes of energy, water, and CO2 over the vegetation, and trace gases from the soil surface.

.- To determine the capacity of these ecosystems to sequester carbon following disturbance.

Why South America??

Four sites were selected

Based on various stages of regrowth/carbon aggradation following disturbance

Cleared savanna where was established a permanent African grass (Andropogon gayanus)

Herbaceous savanna with less than 10% of tree cover (Trachypogon vestitus, A. canescens, dominant species)

Open bush island savanna with 10-50% covers by woody species and a developped grass layer

Woodland with 50-100% of tree canopy cover and sparse gramineous layer

Measurements were carried out during 45 continuous day of the wet and dry season

Estimates of carbon stocks in the plots

Herbaceous component

Woody compartment

above-ground dry mass

below-ground dry mass

Instrumentation used in the measurements

Variable 

Instrumentation

Short-wave radiation (S) K&Z CM3 Pyranometer

Albedo (S) K&Z CM3 Albedometer

Net all-wave radiation (Rn) above to

canopy

CSI Q-7.1 Net radiometer CSIRO S.R.I.4. Net radiometer

Net-all radiation (Rn[0]) behind the canopy Delta-T Devices TRL/M3 Tube net radiometer

Thermocouples CSI. HMP 35C temperature/RH probe

Wind speed and direction RM Young Wind Sentry and VanePSI-30 Teledyne Hastings-Raydist

Latent heat flux (LE) and CO2 flux

 

Measurements conduced at the plots by using two set of eddy covariance equipment involving three axis ultra sonic anemometer (GI Solent A 1012R) and infrared gas analyzer (LICOR 6262)

Soil sensible heat flux CSIRO S.R.I.9. Heat flux plates

Pressure Fortin-type barometer

Precipitation CSI 1E525 Tipping Bucket Rain Gage

Soil volumetric water content Trase 6050x1 Time Domain Reflectometer

Soil respiration LICOR 6000-09 and probe LICOR 6200

RESULTS.

Floristic and structural features

125 Species, 40 families

Annual species: herbaceous 47%

open bush 36%

woodland 18 %

Total diversity throughout the savanna stages increased from 53 to 65 species. Whereas in the cultivated grassfield, it reached 41 species with 70 percent of annuals

Community features Tussock-grassfield(Andropogon

gayanus)

Herbaceoussavanna

Open bushisland

savanna

Woodland savanna

Tree cover (%) ---------- ---------- 19 80

Tree density (trees m-2) ---------- ---------- 0.33 0.73

Tree basal area (m2 ha-1) ---------- ---------- 1.05 13.15

Tree diversity (N species) ---------- ---------- 14 38

Herbaceous diversity (N species) 41 53 44 27

Total diversity (N species) 41 53 58 65

Tussock/grassfield Herbaceous savanna

Open bush island Woodland savanna

Tussock/grassfield Herbaceous savanna

Open bush island Woodland savanna