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Fog in the California Redwood forest: Ecosystem inputs and use by plants

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)

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Fog in the California Redwood forest: Ecosystem inputs and use by plants

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  1. Fog in the California Redwood forest: Ecosystem inputs and use by plants T.E. Dawson

  2. 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

  3. 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

  4. Fog formation • 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 • Enriched in the heavier 2H and 18O 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 2H and 18O

  5. 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

  6. Mixing Models • Proportion of fog water (Pf) used by plants • 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

  7. Results Interception off trees always higher by 18-40% -stripping fog -solar radiation, wind velocities Forested areas have greater input

  8. Redwoods: 8-43% Understory: 6-100% Rooting patterns, water demand, direct absorption through leaves, funnel water

  9. 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

  10. 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

  11. 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

  12. Saguaro Cactus: How important are they? (Wolf and Martinez del Rio)

  13. Saguaro cactus • 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‰ • D = 48.4±1.6 ‰ • Surface water=-37.3 to -23.5‰

  14. 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 Desert Nesting Birds Differences in foraging modes!!

  15. 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

  16. 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

  17. Individual species • Granivorous and frugivorous • Insectivorous (7 of 16 that get 25% diet from cactus)

  18. 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

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