biotic and abiotic drivers of seedling survival in a hurricane-impacted forest

Biotic and Abiotic Drivers of Seedling Survival in a Hurricane-Impacted Forest

Liza S. ComitaColumbia University

Tropical cyclone tracks from 1985 to 2005

Photo credit: Larsen & Torres-Sanchez, USGS

Photo credit:Timo Veijola

Before….

Photo credit:Timo Veijola

And after….

Hurricane Damage

• Abiotic environment– Open up forest canopy ->

increased understory light levels & more heterogeneity

• Biotic environment– Increased light levels-> increased

seedling densities -> density-dependent mortality

Hurricane Disturbance

• How does hurricane disturbance alter the biotic and abiotic environment?

• Which biotic and abiotic factors determine patterns of seedling survival in the understory?

• Does the importance of these factors change as the forest recovers?

Luquillo Experimental Forest, Puerto Rico

•16 ha Forest Dynamics Plot

•138 tree and shrub species•Aseasonal, hurricane-impacted forest (Hugo 1989, Georges 1998)

0 50 100 150 200 250 300

010

020

030

040

050

0

Meters east

Met

ers

north

Seedling census• 2 x 1 m seedling plots• 150 est. in 2000• 63 added in 2004• Tree, shrub, palm

seedlings ≥10 cm tall • Tagged, measured,

identified to species in 2000, 02, 04, 07, 08

• Hemispherical photos taken over each plot to quantify light levels

Light levels (at 1 m above ground)

1999 2002 2004 2007

Year

Mea

n %

tran

smis

sion

010

2030

4050

60 •Significantly higher light levels after the hurricane•Sharp drop within 3 yrs due to canopy closure

Seedling density

2000 2002 2004 2007 2008

Year

See

dlin

g de

nsity

810

1214

1618

20(m

-2) •Higher seedling densities for

several years post-hurricane

Seedling survival as a function of:• Abiotic factors

– Light– Soil

• (5 soils types)

– Topography • (topo category & % slope)

0 50 100 150 200 250 300

010

020

030

040

050

0

Meters east

Met

ers

north

Seedling survival as a function of:• Biotic neighborhood

– Density of • conspecific seedlings • heterospecific seedlings• conspecific tree BA• heterospecific tree BA

• Abiotic x Biotic interactions– Light x Neighbors

Generalized linear mixed effects model

Logit(S)= TIME + LOG(HEIGHT) + LIGHT + LIGHT2 + SLOPE+TOPO+SOILTYPECONS + HETS + CONBA + HETBA+LIGHT:CONS + LIGHT:HETS +LIGHT:CONBA + LIGHT:HETBA

+SPECIES + PLOT

FIXED EFFECTS

RANDOMEFFECTS

‘lme4’ package

• lmer() function• Binomial errors (survival 0/1)• Standardized predictors

– Divide by mean and subtract 1 sd– Makes it easy to directly compare effects for

variables that are measured on different scales

TIME

log (HT)

CONS

HETS

CONBA

HETBA

LIGHT

LIGHT2

CONS x LIGHT

HETS x LIGHT

CONBA x LIGHT

HETBA x LIGHT

Coefficient estimates-0.6 -0.2 0.2 0.6

12

34

56

78

910

1112

All species

-0.5 0.0 0.5 1.0

Shade tolerant

-0.5 0.0 0.5

Intermediate

-0.5 0.0 0.5 1.0

Light demandingRESULTS

Effect of Light

0.0 0.2 0.4 0.6 0.8

0.35

0.40

0.45

0.50

0.55

0.60

Percent transmission

Pro

babi

lity

of s

urvi

val

Effect of Conspecific Seedling Neighbors

0 20 40 60 80 100 120

0.42

0.44

0.46

0.48

0.50

0.52

0.54

Conspecific seedling neighbors

Pro

babi

lity

of s

urvi

val

Light level:

High (trans = 0.50)Mean (trans = 0.21) Low (trans = 0.10)

Effects in each census interval

2000-02 2002-04 2004-07 2007-08LIGHT + 0 0 0CON Seedlings 0 - - +HET Seedlings 0 0 0 0CON BA - - - -HET BA + 0 0 0

Maria Uriarte Jill ThompsonJess Zimmerman Nick BrokawInge JonckheereLFDP technicians & volunteers

Acknowledgements

Email: [email protected]

QUESTIONS?

biotic and abiotic drivers of seedling survival in a hurricane-impacted forest

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