Keystone Species

• Coastal Redwoods• Saguaro Catci

• Sea Birds

Scott Rohlf3/1/10

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 2H and 18O (hence no Rayleigh Distillation in fog)

Methods

• Fog and rain samples– Total input

• Rain, fog, fog drip off trees– Local meteoric water line

• 2H=7.718O+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

ResultsInterception 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

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

IMPACTS:

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

• White-winged Dove• Mourning 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 communityduring periods when they saguaro fruit was not available = +3.3‰– High turnover rate of blood plasmareflects isotopic composition of C incorporated recently

(Wolf and Martinez del Rio, 2002)

Avian Liver and Body Water Results

Mourning Dove• No correlation between

13C 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