Transcript 10-0301_Keystone

Keystone Species
• Coastal Redwoods
• Saguaro Catci
• Sea Birds
Scott Rohlf
3/1/10
Fog in the California
Redwood forest:
Ecosystem inputs and use by
plants
T.E. Dawson
Objectives
• How important is fog as a 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
• Areas with redwoods and without
– Fog observed to not hydrate areas where trees are not
present
Importance of Fog
• Can 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 and stream
flow decrease
• Higher water input/soil
moisture around tree canopies
Fog formation
•
•
•
Interaction between warm air and
recently evaporated water vapor
and cold water (up-welling, or
currents)
Causes condensation---thus fog
Key Point: Heavier then rain
because rains come from storm
systems that have moved great
distances, which causes them to
become depleted in H and O
(hence no Rayleigh Distillation in
fog)
2
18
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
–
Two compartment mixing model (Brunel et
al)
• Assumes water comes from 2
sources
– Fog or Rain
• 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%
Plants in Understory: 6-100%
Rooting patterns, water demand, direct absorption through leaves, funnel water
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
IMPACTS:
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?
(Review)
(Wolf and Martinez del Rio, 2002)
Saguaro cactus
• Succulent CAM
• 4000 or more liters of water
• 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‰
•
D = 48.4±1.6 ‰
– Surface water=-37.3 to -23.5‰
• Other C4 plants consumed by
mammals
• C3=<.5% seed mass in
sampled ecosystem
(Wolf and Martinez del Rio, 2002)
Avian Species
• Mourning Dove
• White-winged Dove
13C - Collected from blood plasma
and liver tissue
D – of body water
(Wolf and Martinez del Rio, 2002)
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 community
during periods when they saguaro fruit was
not available
– = +3.3‰
– High turnover rate of blood plasma
reflects isotopic composition of C
incorporated recently
(Wolf and Martinez del Rio, 2002)
Avian Liver and Body
Water Results
Mourning Dove
• No correlation between
13
 C and D
• Gained only nutrients
(35% total C) for ~3
weeks in July
White-winged Dove
• 13C and D linearly and
positively correlated—fruit
was important for C and
H2O
• Saguaro fruit = >60% of
diet between June and
mid-Sep.
Implies a difference in foraging modes
(Wolf and Martinez del Rio, 2002)
Deuterium
• D of fruit water is enriched
75-100‰
• White-winged Doves
– When using fruit, body water
pools became enriched
• Peak due to evaporative
losses
(Wolf and Martinez del Rio, 2002)
Individual species
• Granivorous and frugivorous and insectivorous
(Wolf and Martinez del Rio, 2002)
Introduced Predators Transform Subarctic
Islands from Grassland to Tundra
• Impacts of introduced
arctic foxes to the
Aleutian Island vegetation
• Observed increased
vegetation on fox free
islands
• Isotopic study to show
whether effects of top
predators can propagate
through multiple trophic
levels
Croll et al., 2005
Preliminary Data
• Sampled during Augusts of
2001-2003
• Fox-free islands had
consistently higher nutrient
values and foliage cover
• Concept: Foxes preying on
sea birds lessen amount of
marine derived nutrients
being deposited on land (i.e.
less bird poop)
Croll et al., 2005
Isotopic Results
• Fox-free islands have
significantly increased
15N over fox-infested
islands
• Experimental plot with
increased nutrient input
on fox-infested island had
24x biomass over the
3yrs
Croll et al., 2005