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