intact rainforest and land-use change in amazônia:

Intact rainforest and Land-use Change in Amazônia:

Scott R. Saleska

Harvard University: S.C. Wofsy, L. Hutyra, A.H. Rice, B.C. Daube, D.M. Matross, E.H. Pyle, J.W. Munger

University of Sao Paulo: P.B. de Camargo, H. de Rocha; INPE: V.W. Kirchhoff;

U.C. Irvine: M.L. Goulden, S.D. Miller

Seeing both the forest and the trees

Land-use change I (obvious):Biomass burning, conversion to

agriculture

Land-use change II (subtle): Treefall destroys research site

Outhouse

Outhouse remnants

Fallen tree

How can both kinds of changes be important?


• “Changed” forest:

High intensity relatively smaller area (e.g. burning, total clearing) (1.9 million ha/year in 1990s)

(Source: Brazilian Space Agency, INPE)

• “Intact” forest: small effect huge area

(~600 million ha)


• “Changed” forest:

High intensity relatively smaller area (e.g. burning, total clearing) (1.9 million ha/year in 1990s)

(Source: Brazilian Space Agency, INPE)

• “Intact” forest: small effect huge area

(~600 million ha)

~0.3% per year change in what that intact forest is doing is comparable to all the land use change

Land-use change II (subtle): Treefall destroys research site

Outhouse

Outhouse remnants

Fallen tree

Santarém

Rio A

mazonas

Rio

Tap

ajós

Km 67

site

Km 83 site

(logged Sept ’01)

Intact rainforest research sites in a

protected reserve: the Tapajós National Forest, near Santarém, Brazil

Profile systeminlets

(8 levels)

58 m: Level 1 Eddy flux

47 m: Level 2 Eddy flux

Part 1: Eddy flux (“the forest”)64m tall tower: Tapajos forest, Km 67

Flux CO2 = w ’ CO2’

w’ = vertical windCO2 = (CO2 + CO2’)

Eddy covariance

-2

-1

0

1

2

m s

- 1

18

20

22

24

oC

0 10 20 30 40 50 60 70 80 90 100332

334

336

338

Seconds

CO2 richCool

CO2 depletedWarm

mo

l C

O2 m

ol

-1

a) w

b) T

c) CO2

(A) Eddy flux of CO2 for eddy1 (58m) and eddy2 (47m);

(B) friction velocity (u*) (turbulence);

(C)mean CO2 concentration 0-60m ("canopy storage");

(D)net ecosystem exchange (NEE = Eddy flux+ <storage change>)

Initial Results: Hourly time series from the Primary Forest eddy flux tower at km 67

On windy nights (10-11 April, u*>0.2 m/s (B)) CO2 efflux (A) is strongly positive, CO2 storage (C) is low, and NEE (D) flux (A).

On calm nights (12-14 April), flux (A) and u* (B) are virtually zero, and CO2 storage is high, causing NEE to be significantly higher than eddy flux.

calm nightswindy nights

10 April 12 April 14 April

Date in 2001

-2000

0

2000

4000

6000

Jul Oct Jan Apr Jul Oct Jan Apr Jul Oct

kg(C

) p

er

ha

0

100

200

pre

cip

(m

m/w

ee

k)

0

100

200

pre

cip

(m

m/w

ee

k)

km83 sitekm67 sitekm83 sitekm67 site

eddyflux

bio-metry

B

upta

kelo

ss t

o

atm

osp

here

start of dry

season

logging at km

83

Sum hourly fluxes to get ecosystem carbon balance over time:

Summary: (1) towers agree with each other;(2) Forest ecosystem is showing net carbon loss (first in Amazonia)

Biometry

Cum

ula

tive

NE

E (

loss

to

atm

osp

here

), k

g C

ha-1

2000 2001 2001

Cumulative Net Ecosystem Exchange (NEE) and precip Average annual

C-balance over two years:

Some Questions

1. Why is the forest not in carbon balance?

2. How does this flux (~ 1 Mg C/ha/yr) compare to those from land-use change?

Part 2 (“the trees”):

Biometric Study of Tapajós Forest, km 67 dendrometers, 1000 trees

dbh tapes, 2800 trees

quantify woody debris, coarse

fine, and litter

net u

ptak

e | n

et C

em

issi

on

grow

th/lo

ss r

ate

(Mg

C h

a-1 y

r-1)

Live Biomass(145-160 tC/ha)

-6-4

-20

24

mortality

growth

recruit

Recruitment, growth, mortality, and dead wood stock directly

measuredlive wood net gain: 1.4 0.6

MgC ha-1 yr-1

Carbon fluxes from live and dead biomass, 1999-2001

net u

ptak

e | n

et C

em

issi

on

grow

th/lo

ss r

ate

(Mg

C h

a-1 y

r-1)


Dead Wood(30 – 45 tC/ha)

-6-4

-20

24

mortality

growth

recruit

mortality

decomp-osition

Best estimate decomposition k (0.120.02 yr-1) based on field

studies near Manaus (Chambers et al. 2001)



MgC ha-1 yr-1

dead wood net loss:

+3.3 1.1


net u

ptak

e | n

et C

em

issi

on

grow

th/lo

ss r

ate

(Mg

C h

a-1 y

r-1)



-6-4

-20

24

whole-forest

net loss:+1.9

1.0

mortality

growth

recruit

mortality

decomp-osition





MgC ha-1 yr-1

dead wood net loss:

+3.3 1.1


net u

ptak

e | n

et C

em

issi

on

grow

th/lo

ss r

ate

(Mg

C h

a-1 y

r-1)



-6-4

-20

24

whole-forest

net loss:+1.9

1.0

mortality

growth

recruit

mortality

decomp-osition




measuredEddy Flux

+1.3 0.9

Net Flux is sensitive to the decomposition rate of the dead wood, k. (Note: This forest would be losing carbon even if decomposition was as low as in a temperate forest in the southern U.S.)

Biometry agreeswith eddy flux

live wood net gain: 1.4 0.6

MgC ha-1 yr-1

dead wood net loss:

+3.3 1.1


Question 1:

Why is this forest not in carbon

balance?

Three observations to consider:

(1) The balance for live wood and dead wood is in opposite directions

net u

ptak

e | n

et C

em

issi

onCarbon fluxes from live and dead biomass, 1999-2001

grow

th/lo

ss r

ate

(Mg

C h

a-1 y

r-1)



-6-4

-20

24

whole-forest

net loss:+1.9

1.0

mortality

growth

recruit

mortality

decomp-osition




measuredEddy Flux,

+1.3 0.9


MgC ha-1 yr-1

dead wood net loss:

+3.3 1.1

Question 1:

Why is this forest not in carbon

balance?

Three observations to consider:

(1) The balance for live wood and dead wood is in opposite directions

(2) Stock of above-ground dead wood is exceptionally large:

• in comparison to other sites;

• relative to what is needed for steady-state

( decade of mortality inputs to accumulate the excess dead wood stock)

net u

ptak

e | n

et C

em

issi

onCarbon fluxes from live and dead biomass, 1999-2001

grow

th/lo

ss r

ate

(Mg

C h

a-1 y

r-1)



-6-4

-20

24

whole-forest

net loss:+1.9

1.0

mortality

growth

recruit

mortality

decomp-osition




measuredEddy Flux,

+1.3 0.9


MgC ha-1 yr-1

dead wood net loss:

+3.3 1.1

Recruitment Growth

Net = 1.5 Mg C ha-1yr-1

MortalityOutgrowth

32

10

-1-2

-3

flux,

MgC

ha-1

yr-1

Flux from Biomass & Changes in tree number density,

by size class

Observation 3:

Demographic shift:

(a) The increase in flux to biomass isin the smaller size

classes

(b) Corresponding increase in density

of tree stems in the smaller size

classes

Question 1 (cont’d):

Why is this forest not in carbon balance?

95% Conf. on each bin

upta

kelo

ss t

o

atm

osp

here

Recruitment Growth

Net = 1.5 Mg C ha-1yr-1

MortalityOutgrowth

32

10

-1-2

-3

flux,

MgC

ha-1

yr-1

RecruitmentNet

MortalityOutgrowth

10 35 60 85 110 135 160 185

-20

020

40

size class, cm DBH

dens

ity c

hang

e, s

tem

s ha

-1

Flux from Biomass & Changes in tree number density,

by size class Question 1 (cont’d):


95% Conf. on each bin

upta

kelo

ss t

o

atm

osp

here

Observation 3:

Demographic shift:

(a) The increase in flux to biomass isin the smaller size

classes

(b) Corresponding increase in density

of tree stems in the smaller size

classes

Hypothesis:

Tapajós forest site is recovering from recent

episode(s) of disturbance which:

(1) Caused sharply elevated mortality preceeding onset of

this study.

(2) Caused a large increase in dead wood pool

(to the point where losses exceed inputs)

(3) Opened canopy gaps causing significant new

growth and recruitment into smaller size classes of live

wood (making overall growth uptake exceptionally high)

Question 1:


Hypothesis:

Tapajós forest site is recovering from recent

episode(s) of disturbance which:

(1) Caused sharply elevated mortality preceeding onset of

this study.

(2) Caused a large increase in dead wood pool

(to the point where losses exceed inputs)

(3) Opened canopy gaps causing significant new

growth and recruitment into smaller size classes of live

wood (making overall growth uptake exceptionally high)

Question 1:

Why is this forest not in carbon balance? Perhaps contributed to by

recent El Niňo droughts?

Condit et al. (1995), Williamson et al. (2000) link El Nino to elevated

tree mortality

Summary:• Net Carbon loss, because respiration losses from

excess dead wood dominate gains from tree growth

transient disturbance-recovery dynamic – possibly typical of old-growth forest, but not seen in eddy flux studies so far

Source: Moorcroft, Hurtt & Pacala (2001)

Modeled flux following disturbance in gap of a “balanced-biosphere” rainforest near Manaus

Gap Age (time since disturbance in years)

Mg (

C)

ha

-1 y

r-1

2520

15

10

5

-5

0

-10

-15

-20

-25

Tapajos Km 67

site(loss)

npp = net primary productivity (uptake)rh = heterotrophic respiration (loss) nep = net ecosystem productivity (change in carbon balance)




Implications for Land-use change:• Intact forest is dynamic: small changes in

dynamics caused by human-induced changes in global climate can have effects comparable to more obvious land-use change:





dynamics caused by human-induced changes in global climate can have effects comparable to more obvious land-use change:– rising CO2 could stimulate forest, causing more carbon

uptake





dynamics caused by human-induced changes in global climate can have effects comparable to more obvious land-use change:– rising CO2 could stimulate forest, causing more carbon

uptake– Global warming could increase El Niño droughts, and

forest disturbance, causing more carbon loss




Mg (

C)

ha

-1 y

r-1

2520

15

10

5

-5

0

-10

-15

-20

-25

Tapajos Km 67

site(loss)





Mg (

C)

ha

-1 y

r-1

2520

15

10

5

-5

0

-10

-15

-20

-25

Tapajos Km 67

site(loss)

Amount of change in nep, that, spread across the intact Amazon, would be ~twice that from deforestation: ±1 Mg ha-1 yr-1 x 600 million ha= ±0.6 Pg yr-1

`





Mg (

C)

ha

-1 y

r-1

2520

15

10

5

-5

0

-10

-15

-20

-25

Tapajos Km 67

site(loss)

Amount of change in nep, that, spread across the intact Amazon, would be ~twice that from deforestation: ±1 Mg ha-1 yr-1 x 600 million ha= ±0.6 Pg yr-1

versus

0.3 Pg yr-1 lost from Amazonian deforestation

(~1.4 Pg yr-1 global deforest.)

`



excess dead wood dominate gains from tree growth transient disturbance-recovery dynamic –

possibly typical of old-growth forest, but not seen in eddy flux studies so far

Implications for Land-use change:• Intact forest is dynamic: small changes in dynamics

caused by human-induced changes in global climate can have effects comparable to more obvious land-use change:– rising CO2 could stimulate forest, causing more carbon

uptake– Global warming could increase El Niño droughts, and forest

disturbance, causing more carbon loss

• Integrated analysis of different kinds of change needed for full understanding of consequences of land-use change

Biometry plots upwind of flux tower, with locations & sizes of all trees >35cm, subset>10cm DBH

Transects (from 35 cm DBH)

(inset) Coarse Woody Debris Plots

Legend for CWD Plots

plot size of wood # area

> 30cm

10 - 30 cm

2 - 10 cm

32

64

64

1200 m2

25 m2

1 m2

tower

(20 ha, 2800 trees, stratified)

N

Questions

• Land-use Change: change relative to what?(i.e. what did the land do before its use was changed?)

• What is “change”?- forest conversion, often by fire, to

agricultural or grazing lands- Logging- Global climate change

Q: Is there “lost flux”?

We expect total nighttime NEE (which depends only on the physiology of forest respiration), to be essentially independent of atmospheric turbulence.

Definition: Net Ecosystem Exchange:

NEE = Eddy Flux + <canopy storage>

Flux out the top

“Storage flux”

“Turbulence” (e.g. U* = friction velocity)

Idealized Relations:

NEE components, however, are expected to depend on turbulence, but in opposite directions.

-10

010

20

NEE

-10

010

20

Ed

dy

Flu

x

“shut-off” of eddy transport at low

turbulence…

-10

010

20

Sto

rage

Flu

x

… leads to compensating build-up

of CO2 in canopy

dtd



Observed Relations:

Fall-off in NEE for U*<0.2

Answer: Yes, it looks like it. As U* 0, eddy flux decreases and storage flux increases as expected, but their sum (NEE) declines for U* < 0.2 m/sec:



Observed Relations:

Fall-off in NEE for U*<0.2

Answer: Yes, it looks like it. As U* 0, eddy flux decreases and storage flux increases as expected, but their sum (NEE) declines for U* < 0.2 m/sec:

We take this as evidence of lost flux.

Solution: filter out data below some U* threshold, then fill by interpolation

“lost flux”

-6000

-4000

-2000

0

2000

4000

Jul Oct Jan Apr Jul Oct Jan Apr Jul Oct2000 2001 2002

kg(C

) pe

r ha

0100200

prec

ip

(mm

/wee

k)

A

0100200

prec

ip

(mm

/wee

k)

0100200

prec

ip

(mm

/wee

k)

0100200

prec

ip

(mm

/wee

k)

km83 sitekm67 sitekm83 sitekm67 site

eddyflux

bio-metry

B

upta

kelo

ss t

o

atm

osp

here

uncorrectededdy flux

km67

km83

Cumulative Net Ecosystem Exchange (NEE) and precip

Average annual C-balance

start of dry

season

logging at km

83

Summary: (1) with U* correction, towers agree with each other;

(Part 1)

intact rainforest and land-use change in amazônia:

Documents

flux co2

forest ecosystem

inpe intact forest

tapajos forest

co2 storage c

primary forest eddy

tapajs national forest

nee d flux