gotsch, sybil

Life in the treetops: Ecophysiological strategies in canopy epiphyte communities along a microclimate gradient in the tropical montane cloud forest

Sybil G. Gotsch1, Nalini Nadkarni2, Alexander Darby1, Andrew Glunk1, Mackenzie

Dix1, Kenneth Davidson1, Todd Dawson3

1Department of Biology, Franklin and Marshall College, Lancaster, PA, USA 2 Department of Biology, University of Utah, Salt Lake City, UT, USA 3 Department of Integrative Biology, University of California at Berkeley, CA, USA

Tropical Montane Cloud Forests (TMCF) • Highland forests in the tropics that are frequently

covered in clouds or mist • Exceedingly high biodiversity and endemism • Important role in local and regional hydrology

Role of Epiphyte Community in Ecosystem Processes in the TMCF

• 5-20% of water inputs due to water stripping from clouds • Epiphytes play major role in interception of cloud water • Up to half total nutrient pool in canopy may be due to

epiphytes • Dependence on cloud water may make these

communities very vulnerable to changes in climate

In the TMCF of Costa Rica, climate has already begun changing

• General Trends since 1971 – Annual rainfall has been increasing – Variability in rainfall has been increasing – Number of days without rain in a year has been

increasing – Number of 3-5 day periods without rain has been

increasing

Pounds et al. 1999, Pounds pers. comm.

1. What are the ecophysiological strategies of

epiphytes in a TMCF and in canopy communities across a gradient in microclimate?

2. How is transpiration affected by the TMCF microclimate?

1. How does microclimate vary in a tropical montane cloud forest region?

Research Questions

The TMCF of Monteverde, Costa Rica

• Elevation 1480-1500 m • Rainfall 3000-5000mm • 500-2000mm of cloud

water inputs

Significant trait variation across species within a single site

• Stem Density: 3-fold variation • Specific Leaf Area: 3-fold variation • Leaf toughness: varied 2.5-fold, though values

were generally high (> 600gm). • Leaf thickness: 4-fold variation • Hydrenchymal Thickness: 10-fold variation • Plants exhibit a variety of strategies • No clear grouping based on life form

Gotsch et al. 2015

• Clear diurnal patterns during sunny periods following rain

• FWU occurs

when leaves are wet

• Variation

across species

Dry Season Foliar Water Uptake in the Monteverde Cloud Forest Reserve

What are the drivers of sap flow in epiphytes??

Hierarchical linear model, parameters included: vapor pressure deficit, air temperature, leaf wetness, wind speed, soil moisture, soil temperature, visibility and solar radiation 1. Overall Transpiration: Canopy soil water most important driver

• More transpiration when soil well hydrated 2. Foliar water uptake: Precipitation most important driver

• More FWU during rainy periods 3. Nighttime flow: Visibility most important driver.

• Less NF during clear nights, more NF during cloudy nights • NF likely refilling in epiphytes rather than transpiration Darby et al. in prep

How do epiphyte communities under, in and above the clouds function differently?

Measurements Microclimate: Canopy station-air temp/RH, leaf wetness, soil moisture/temp, wind speed/direction

Plant-based measures (1425 samples to date) • Functional Trait Analysis: stem density,

specific leaf area, leaf dry matter content, leaf toughness, stomatal density

• Anatomical measures: Leaf thickness, cuticle thickness, hydrenchymal thickness

• Water relations: turgor loss point, bulk elastic modulus, relative water content at the TLP, etc.

• 38 species representing 11 families and 4 growth forms

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1 site 2 sites 3 sites 4 sites 5 sites 6 sites

% o

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ecie

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Variation in Microclimate

Variation in Traits

• Functional Traits: – Toughness, generally high (>

750 g) but no clear trend in variation

– SLA/LDMC/WD little variation across sites

• Water Relations Traits – Many traits tend to vary in a

predictable pattern across the gradient

Photo Credit: Eric Stearley

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UGA BuenAmigo

Lower CC Upper CC CCT-Lab El Valle

Sto

mat

al D

ensit

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tom

./m

m^2

)

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-1

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ΨTL

P (M

Pa)

74

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92

UGA BuenAmigo


RWC

at th

e TL

P (%

)

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0.7

UGA BuenAmigo


Hydr

ench

ymal

thic

knes

s (m

m)

Interspecific Variation in Water Relations Traits

Plants in drier sites are more succulent AND have lower turgor loss points

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UGA Buen Amigo Lower CC

Mea

n St

omat

al D

ensit

y (S

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ata/

mm

^2)

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Mea

n To

tal H

ydro

(mm

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Intraspecific variation across the three driest sites (Anthurium scandens, Clusia palmana, Peperomia sp, Macleanea insignis, Peperomia hoffmannii)

In the wettest three sites, no clear pattern across sites. SD generally higher.

-1.8

-1.6

-1.4

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-1

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ΨTL

P (M

Pa)

76

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Rela

tive

Wat

er C

onte

nt a

t th

e TL

P (%

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R² = 0.2177

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-2

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-1

-0.5

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Turg

or Lo

ss P

oint

(Mpa

)

Stomatal Density (stomata/mm2)

R² = 0.282

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Hydr

ench

yma

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m)

Stomatal Density (stomata/mm2) R² = 0.4888 -3

-2

-1

00 100 200 300

R² = 0.3142

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Upper CC and CCT

Upper CC

Microclimate variability in the mid elevation sites may be driving trait correlations

What have we learned from the epiphyte community?

• Transpiration is very responsive to changes in atmospheric conditions

• Foliar uptake occurs frequently and comprises a significant portion of whole plant water balance

• Parameters that relate to habitat moisture are the most important drivers of sap flow.

• Variation in water relations traits indicate that the epiphyte community in drier sites can both avoid and withstand drought better than in wetter sites.

• Trait relationships maybe driven by variation in microclimate in the mid-elevation sites

Next Steps

• Dry season sap flow in three sites along the gradient • Dry season leaf water potentials • Quantification of abundance via biomass in all six sites • Dry-down experiment on common species from three

sites to link traits with drought resilience

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UGA BuenAmigo

Lower CC Upper CC Reserve El Valle

Epip

hyte

Abu

ndan

ce (%

)

UGA

Lower CC Reserve

gotsch, sybil

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