Progress in understanding carbon dynamics in primary forests

CD08 team

Stock(e.g. biomass,

soil C)

Input Output

Mean Residence Time = Stock/Output

How many of us model Carbon dynamics

Stock(e.g. biomass,

soil C)

Input Output

Mean Residence Time = Stock/Output

How many of us model Carbon dynamics

Input Output

Mean Residence Time = Stock/OutputNOT necessarily = Mean age of C in stocks

The better model:

Fast cycling components

Slower cycling components

50

150

250

350

450

550

1950 1960 1970 1980 1990 2000

14C

‰

atmosphere

atmosphere, lagged 3 years

0-5 cm,

Surface litter

0-5 cm soil

-200

-100

0

100

200

300

400

1945 1965 1985 2005

atmosphere

10 cm

22 cm40 cm

Modeling turnover time using changes in bomb radiocarbon

Requires C to have both rapidly and slowly cycling components;

Like trees, soils cannot be modeled

as single homogeneous C

pools

Trees

How old are tropical trees?

How fast do they grow?

How long do they store carbon?

How do characteristics vary across the Amazon basin?

Measurement of tree diameter during establishment of permanent plot

Rio Branco

Manaus

Santarém

Field sites

All terra firme forestSoils are OxisolsVariation in dry season length:Shortest in Manaus, longer in Rio Branco, Santarém

Paragominas

Growth rates from

dendrometer bands

(Vieira et al., Oecologia 2004)

Man

aus

DM

DV

(m

day

-1)

-5

0

5

10

15

0

5

10

15

20

25

30

Rainfall Diameter Variation

Rai

nfal

l (m

m d

ay-1

)

Rio

Bra

nco

DM

DV

(m

day

-1)

0

5

10

15

20

25

0

2

4

6

8

10

12

Rai

nfal

l (m

m d

ay-1

)

S

anta

rém

DM

DV

(m

day

-1)

-5

0

5

10

15

20

25

0

3

6

9

12

15

R

ainf

all (

mm

day

-1)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Radiocarbon growth rate (cm/yr)

De

nd

rom

ete

r g

row

th r

ate

(c

m/y

r)

Radiocarbon and dendrometers agree Trees grow slowly

10-30cm

30-50cm

>50cm

ManausRio BrancoSantarém

Little trees grow slower than big trees

Trees in Manaus grow ~2x slower than other areas

0

20

40

60

80

100

120

140

160

180

0-50

50-1

00

100-

300

300-

500

>500

0-50

50-1

00

100-

300

300-

500

>500

0-50

50-1

00

100-

300

300-

500

>500

10-30

30-50

>50

No

Indi

vidu

als/

ha

Manaus

Santarém Rio Branco

Trees can be oldExtrapolating growth rates, we estimate >20% of all trees and 15-35% of trees 10-30 cm diameter are

>300 yrs old

Age of individuals estimated from diameter/growth rate (yr)

Limited radiocarbon data available agree qualitatively with age structure based on Monte Carlo

extrapolation of dendrometer growth rates

0

10

20

30

40

50

60

Manaus(n=35)

Santarem(n=22)

Rio Branco(n=27)

Model (n>3000)

Radiocarbon (n given)

% o

f in

divi

dual

s w

ith a

ge >

300

year

s

Trees <10cm DBH sampled in Rio Branco (Catuaba Reserve) support this picture:

6 of 18 (33%) had ages >45years

0

1

2

3

4

5

1 to 10 10 to 20 20 to 30 30 to 45 >45

Clearing

intact forest

Basal age (years) from radiocarbon

No

of in

divi

dual

s

Manaus

Santarém Rio Branco

Individuals/ha 626 460 466Biomass C MgC/ha 180 141 95Growth MgC/ha/yr 1.6-2.1 2.2 -3.0 3.3-3.4Mean age of C (yr)* 260 220 240 MRT of C (stock/growth)** 114 74 53 * From monte carlo simulations **biomass-weighted Data from Vieira et al. 2004

C dynamics differ with forest location

How can MRT of C in wood be less than the mean age of C in standing

wood?

Standing stock (180 MgC/ha)Mean age ~260 yrGrowth

~2 MgC/ha/yr

Mortality~2 MgC/ha/yrMean age C ~90 yr

Probability of mortality is not the same for all trees – younger, or faster growing, trees tend to die more frequently

Need better understanding of what causes tree mortality

• Low carbon use efficiency (NPP/GPP ~ 30% at Manaus and Santarém sites)

• ~25% of NPP used for wood growth at Manaus (data pending for other sites)

• Although biomass may recover quickly through fast-growing pioneer species, slow growing species (therefore biodiversity) will take centuries to recover from disturbance

Implications of low growth rates:

Conclusions: Models of forest dynamics need to account for:

• Heterogeneity of C in wood and soil pools (age of standing stock > age of C in dying wood; age of C in soils> age of C respired)

• Low allocation of C to wood growth

• Differences in wood dynamics and forest structure across the Amazon basin