Compositional Shifts in Compositional Shifts in Undisturbed Neotropical Undisturbed Neotropical

Forests: Effects of Forests: Effects of Climate Change?Climate Change?

William F. LauranceWilliam F. Laurance1,21,2 & Richard Condit & Richard Condit11  

11Smithsonian Tropical Research Institute, PanamaSmithsonian Tropical Research Institute, Panama22Biological Dynamics of Forest Fragments Project, Biological Dynamics of Forest Fragments Project,

Manaus, Brazil Manaus, Brazil 

Atmospheric COAtmospheric CO22

• Pre-industrial level was Pre-industrial level was 280 ppm280 ppm

• Current level (378 Current level (378 ppm) is highest in last ppm) is highest in last 20 million years20 million years

• In experiments, In experiments, elevated COelevated CO22 increases increases photosynthesis, growth, photosynthesis, growth, and water-use and water-use efficiency for most efficiency for most plants (for tropical plants (for tropical trees, only seedlings trees, only seedlings assessed)assessed) 310

320

330

340

350

360

370

380

1960 1970 1980 1990 2000

CO

2 c

once

ntra

tion

(ppm

)

Year

Data from Mauna Loa, Hawaii

Evidence for Evidence for pervasive pervasive

changes in changes in Amazonian tree Amazonian tree

communitiescommunities

W. F. Laurance W. F. Laurance et al.et al. (2004) Pervasive (2004) Pervasive alteration of tree communities in undisturbed alteration of tree communities in undisturbed Amazonian forests. Amazonian forests. NatureNature 428428:171-175:171-175

18 1-ha plots in forest interiors18 1-ha plots in forest interiors Monitored 11-19 yearsMonitored 11-19 years 115 most abundant genera115 most abundant genera

Study Design:Study Design:

Changes in Central AmazoniaChanges in Central Amazonia1)1) Concerted shifts in species Concerted shifts in species

composition (14 times more composition (14 times more than expected by chance), than expected by chance), with fast-growing canopy with fast-growing canopy and emergent trees evidently and emergent trees evidently gaining a competitive gaining a competitive advantage over smaller, advantage over smaller, slower-growing treesslower-growing trees

2)2) Accelerating forest dynamicsAccelerating forest dynamics

3)3) Accelerating growth for most Accelerating growth for most generagenera

Barro Barro Colorado Colorado Island Island

-1500 ha in area-1500 ha in area-isolated in 1914-isolated in 1914

50-hectare 50-hectare plot plot

BCI 50-ha PlotBCI 50-ha Plot Established in 1982, recensused in 1985, 1990, 1995, 2000Established in 1982, recensused in 1985, 1990, 1995, 2000 Subdivided into 50 1-ha plotsSubdivided into 50 1-ha plots Included only species present in Included only species present in >>10 1-ha plots and 10 1-ha plots and >>10 cm dbh 10 cm dbh

(142 species)(142 species) Bootstrapping used (at 1% alpha level) to assess changes in density Bootstrapping used (at 1% alpha level) to assess changes in density

and basal area for each species between 1985 - 2000and basal area for each species between 1985 - 2000

BCI: Changes in Tree Density and Basal AreaBCI: Changes in Tree Density and Basal Area

Tree Density:Tree Density:

-19 increased (13%)-19 increased (13%)

-23 decreased (16%)-23 decreased (16%)

Tree Basal-Area:Tree Basal-Area:

-22 increased (15%)-22 increased (15%)

-20 decreased (14%)-20 decreased (14%)

Overall:Overall:

-Nearly 30 times -Nearly 30 times more significant more significant changes than changes than expected by chanceexpected by chance

-10

-8

-6

-4

-2

0

2

4

6

-10 -5 0 5

WinnersLosersOthers

An

nu

al C

ha

ng

e in

Ba

sal A

rea

(%)

Annual Change in Density (%)

Amazonia: Differences in Growth FormAmazonia: Differences in Growth Form

0

20

40

60

80

100

Winners Losers

X2=10.15, d.f.=1, P=0.001

Canopy or emergentsSubcanopy trees

Pe

rcen

t o

f g

en

era

BCI: No Differences in Growth FormBCI: No Differences in Growth Form

0

20

40

60

80

100

120

Winners Losers

X2=0.20, d.f.=1, P=0.65

Canopy or emergentsSubcanopy trees

Pe

rcen

t o

f g

en

era

spec

ies

Amazonia: Larger Trees are WinningAmazonia: Larger Trees are Winning

10 20 30 40 50-40

-30

-20

-10

0

10

20

30

Rs = 0.315, P = 0.0006

Increasing generaDecreasing generaOther genera

Mean trunk diameter (cm)

Ch

an

ge

in d

en

sit

y (%

)

I

I

BCI: No Effect of Tree SizeBCI: No Effect of Tree Size

100 1000-10

-8

-6

-4

-2

0

2

4

Rs= 0.003, P=0.99

WinnersNo changeLosers

Mean tree diameter (mm)

Den

sit

y c

ha

ng

e (%

/ye

ar)

Amazonia: Winners Grow FasterAmazonia: Winners Grow Faster

0

2

4

6

8

10

<1 1-2 2-3 3-4 4-5

t=2.28, d.f.=24, P=0.032

LosersWinners

Nu

mb

er o

f g

ene

ra

Growth rate (mm yr-1)

BCI: No Difference in Growth RateBCI: No Difference in Growth Rate

0

2

4

6

8

10

<1 1-2 2-3 3-4 >4

t= -1.38, d.f.=54P=0.18

LosersWinners

Nu

mb

er o

f g

ene

ra

Growth rate (mm yr-1)

spec

ies

Amazonia: Accelerating Forest DynamicsAmazonia: Accelerating Forest Dynamics

0

0.5

1

1.5

2

1984-1991 1992-1999

MortalityRecruitment

An

nu

al

rate

(%

)

Interval

BCI: Decelerating Forest DynamicsBCI: Decelerating Forest Dynamics

0

0.5

1

1.5

2

2.5

3

1982-1985 1985-1990 1990-1995 1995-2000

MortalityRecruitment

An

nu

al r

ate

(%)

Interval

Mortality:Mortality:

-1982-85 is higher -1982-85 is higher than the other than the other intervalsintervals

-1995-2000 is -1995-2000 is higher than 1990-95higher than 1990-95

Recruitment:Recruitment:

-1982-85 and -1982-85 and 1985-90 are higher 1985-90 are higher than both 1990-95 than both 1990-95 and 1995-2000and 1995-2000

-1990-95 is higher -1990-95 is higher than 1995-2000than 1995-2000

Amazonia: Accelerating Growth RatesAmazonia: Accelerating Growth Rates

Growth accelerated Growth accelerated more for winners more for winners than losersthan losers– Winners: 57% Winners: 57% – Losers: 22% Losers: 22% – Other genera: 40%Other genera: 40%

0.1

1

0.1 1

t=9.74, P<0.00001Paired t-test

WinnersLosersOthersG

row

th r

ate

(m

m y

r-1):

In

terv

al 2

Growth rate (mm yr-1): Interval 1

BCI: Decelerating Growth RatesBCI: Decelerating Growth Rates

0

1

2

3

4

5

82-85 85-90 90-95 95-00

An

nu

al

Rate

(m

m)

1

10

1 10

t=4.71, P<0.0001Paired t-test

Gro

wth

Rat

e 1

985-

90

(m

m/y

r)

Growth Rate 1982-85 (mm/yr)

-Growth was higher -Growth was higher in 1982-85 than in all in 1982-85 than in all other intervals other intervals ((PP<<0.0001)0.0001)

-Growth was also -Growth was also higher in 1985-90 higher in 1985-90 than in the final two than in the final two intervals (Pintervals (P<<0.0003)0.0003)

What is Driving the Tree-What is Driving the Tree-Community Changes on BCI?Community Changes on BCI?

1)1) BCI is a forest fragmentBCI is a forest fragment

2)2) Parts of BCI are Parts of BCI are recovering from recovering from past disturbancespast disturbances

– 70-150 year-old 70-150 year-old regrowth near the regrowth near the plot: previous source plot: previous source of successional-plant of successional-plant propagulespropagules

– Successional species Successional species are now declining on are now declining on the plotthe plot

3)3) BCI has experienced a long-term drying trend and BCI has experienced a long-term drying trend and recent severe droughtsrecent severe droughts

1000

2000

3000

4000

1930 1940 1950 1960 1970 1980 1990 2000

An

nu

al ra

infa

ll (

mm

)

Year

Population Trends vs. Drought TolerancePopulation Trends vs. Drought Tolerance

-10

-5

0

5

0.1 1 10

Rs= -0.164

P=0.051

An

nu

al c

ha

ng

e (%

)

Moisture-demand index

ConclusionsConclusionsTree-community changes in central Amazonia Tree-community changes in central Amazonia

are consistent with elevated productivity, are consistent with elevated productivity, possibly from rising COpossibly from rising CO22 levels levels

Changes are BCI seem to be driven by recent Changes are BCI seem to be driven by recent droughts and possibly nonequilibrium droughts and possibly nonequilibrium conditions on the plotconditions on the plot

The drivers of change may differ among The drivers of change may differ among different forests. Thus, there is a dire need for different forests. Thus, there is a dire need for more long-term studies of tree-community more long-term studies of tree-community dynamics that explicitly test global-change dynamics that explicitly test global-change hypotheseshypotheses

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