Transcript Keystone_species_lecture

Fog in the California
Redwood forest:
Ecosystem inputs and use by
plants
T.E. Dawson
Objectives
• Is fog an important source of moisture for the plants
that inhabit the ecosystem
– Redwoods use 600±145 L/day (45 m tree)
– Greatest demand during summer when rain is sparse, but fog
is common
– During summer, deep soil water may become unavailable for
shallow rooted species
– How much is actually used, not just stored?
• Areas with redwoods and without
– Trees significance in influencing the magnitude of fog water
input into the ecosystem
Importance of Fog
• Ecosystem nutrient balance or
aspects of biochemistry
• Reduce plant moisture stress
by reducing canopy
transpiration or evaporation
from habitat
• Improve plant water status by
direct absorption
• When trees are removed water
input from fog drip deceases
and so does streamflow
• Higher water input/soil
moisture around tree canopies
Fog formation
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Heaviest from midnight to early or
mid-morning
Interaction between warm air and
cold water (up-welling, or currents)
Causes condensation---thus fog
Doesn’t require condensation
nuclei like clouds
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Enriched in the heavier H and O
isotopes relative to water source
(ocean)
Heavier then rain because rains
come from storm systems that
have moved great distances,
which causes them to become
depleted in H and O
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Methods
• Fog and rain samples
– Total input
• Rain, fog, fog drip off trees
– Local meteoric water line
• 2H=7.718O+9.6
• Provided a mixing line that
was more useful for
interpretation local variations
• Plant and soil samples
• Plant water use
– Whole tree transpiration
– Sapflow sensors
• Different size trees
Mixing Models
• Proportion of fog water (Pf)
used by plants
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Two compartment mixing model (Brunel et
al)
• Assumes water comes from 2
sources
– Fog and rain
– Deep soil/groundwater
• Weighted values-not all
sources are equally available
Results
Interception off trees always higher
by 18-40%
-stripping fog
-solar radiation, wind
velocities
Forested areas have greater input
Redwoods: 8-43%
Understory: 6-100%
Rooting patterns, water demand, direct absorption through leaves, funnel water
Water use patterns
• Fraction of fog within xylem that was used
• 13-45% of all water used annually
– Smaller trees used more
• Obtain ~19% from fog
– Water use is higher in summer when trees
take up and use more fog water
– More important source than isotopic
information implies
El niño: ratio of rainfall to fog water input higher (less fog), Pf and coefficient of variation increased
-plant demand for water was highest in summer when there was no rain, and fog inputs did occur
Dry: Less rain in winter, so more dependence on fog in summer
VS.
Intact forests increase annual income of water
-if moisture inputs decline, so do nutrient inputs,
decomposition and mineral cycling
-therefore, tree loss = more drought prone,
warmer, open ecosystem
-plants will experience more water stress
Saguaro Cactus:
How important are they?
(Wolf and Martinez del Rio)
Saguaro cactus
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Succulent CAM
4000 or more liters of water
300 flowers, 50-60% fruit
A ton of pollen, nectar, fruit—to
attract pollinators and seed
dispersers
Produce fruit during driest
months (June-July)
Fruit : water and sugar
Seeds: protein, lipids and
carbs
13C = -13.1±0.2‰
– Most common C3= -24.9 ±0.2‰
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D = 48.4±1.6 ‰
– Surface water=-37.3 to -23.5‰
Desert Nesting Birds
Mourning Dove
• Gained only nutrients
(35% total C) for ~3
weeks in July
• No correlation between
13C and D
White-winged Dove
• Saguaro fruit = >60% of
diet between June and
mid-Sep.
• 13C and D linearly and
positively correlated—fruit
was important for C and
H2O
Differences in foraging modes!!
Importance for community of Sonoran
Desert birds…
• Determining proportion of diet that is
represented by two isotopic sources:
isotopic composition of 2 sources
– tissue= p(1 + ) + (1-p)(2 +  )
Isotopic discrimination factor( tissue- diet)
fraction of diet incorporated into focal tissue
• Blood plasma
– Stable C3 resource signal in bird plasma
during periods when they saguaro fruit was
not available
– Thus- = +3.3‰
– Reflects isotopic composition of C
incorporated recently
• 13C of plasma during
summer showed distinct
swell—coresponds to
Saguaro input into
ecosystem
• without: 13C= -21.6‰
• with: 13C= -16‰
• 43% of avian
community’s carbon
derived from fruit
• Lasted for ~ 6 weeks
Individual species
• Granivorous and frugivorous
• Insectivorous (7 of 16 that get 25% diet from
cactus)
Deuterium
• D of fruit water is enriched
75-100‰
• White-winged Doves
– When using fruit, body water
pools became enriched
– Strong correlation between C
and D
• Body water discrimination
factor
– Enriched above fruit
• Evaporation
• But…the presence or absence
of a correlation between  13C
and D can be used to
determine whether birds feed
on seeds, or pulp as well