Keystone Species

• Coastal Redwoods• Saguaro Catci

• Sea Birds

Scott Rohlf3/1/10

Fog in the CaliforniaRedwood forest:

Ecosystem inputs and use byplants

T.E.Dawson

Objectives

• How important is fog as a source of moisture for theplants 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 notpresent

Importance of Fog

• Can reduce plant moisturestress by reducing canopytranspiration or evaporationfrom habitat

• Improve plant water status bydirect absorption

• When trees are removedwater input from fog drip andstream flow decrease

• Higher water input/soilmoisture around tree canopies

Fog formation• Interaction between warm air and

recently evaporated water vaporand cold water (up-welling, orcurrents)

• Causes condensation---thus fog• Key Point: Heavier then rain

because rains come from stormsystems that have moved greatdistances, which causes them tobecome depleted in 2H and 18O(hence no Rayleigh Distillation infog)

Methods

• Fog and rain samples– Total input

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

• δ2H=7.7δ18O+9.6• Provided a mixing line that

was more useful forinterpretation 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 (Brunelet al)

• Assumes water comes from 2sources– Fog or Rain

• Weighted values-not allsources are equally available

ResultsInterception off treesalways higher by 18-40%

-stripping fog-solar radiation, windvelocities

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:

SaguaroCactus:How importantare 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• δ13C = -13.1±0.2‰

– Most common C3= -24.9 ±0.2‰• δD = 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

δ13C - Collected from blood plasmaand liver tissue

δD – of body water

(Wolf and Martinez del Rio, 2002)

Importance for community of SonoranDesert birds…

• Determining proportion of diet that isrepresented by two isotopic sources:

isotopic composition of 2 sources

– δtissue= p(δ1 + Δ) + (1-p)(δ2 + Δ ) Isotopic discrimination factor(δ tissue- δdiet) fraction of diet incorporated into focal tissue

• Blood plasma– Stable C3 resource signal in bird communityduring periods when they saguaro fruit wasnot available– Δ= +3.3‰– High turnover rate of blood plasmareflects isotopic composition of Cincorporated recently

(Wolf and Martinez del Rio, 2002)

Avian Liver and BodyWater Results

Mourning Dove• No correlation between δ

13C and δD• Gained only nutrients

(35% total C) for ~3weeks in July

White-winged Dove• δ13C and δD linearly and

positivelycorrelated—fruit wasimportant for C and H2O

• Saguaro fruit = >60% ofdiet between June andmid-Sep.

Implies a difference in foraging modes(Wolf and Martinez del Rio, 2002)

Deuterium• δD of fruit water is enriched

75-100‰• White-winged Doves

– When using fruit, body waterpools became enriched

• Peak due to evaporativelosses

(Wolf and Martinez del Rio, 2002)

Individual species

• Granivorous and frugivorous and insectivorous

(Wolf and Martinez del Rio, 2002)

Introduced Predators Transform SubarcticIslands from Grassland to Tundra

• Impacts of introducedarctic foxes to theAleutian Island vegetation

• Observed increasedvegetation on fox freeislands

• Isotopic study to showwhether effects of toppredators can propagatethrough multiple trophiclevels

Croll et al., 2005

Preliminary Data• Sampled during Augusts of

2001-2003• Fox-free islands had

consistently higher nutrientvalues and foliage cover

• Concept: Foxes preying onsea birds lessen amount ofmarine derived nutrientsbeing deposited on land(i.e. less bird poop)

Croll et al., 2005

Isotopic Results• Fox-free islands have

significantly increased δ15N over fox-infestedislands

• Experimental plot withincreased nutrient inputon fox-infested islandhad 24x biomass overthe 3yrs

Croll et al., 2005