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Volcanic eruption effects on temperate and boreal tree growth

Volcanic eruption effects on temperate and boreal tree growth . Nir Y Krakauer 1* , Nicole V Smith 1 , James T Randerson 2 1. Geological and Planetary Sciences, Caltech 2. Earth Systems Science, UC Irvine * niryk@caltech.edu. Motivation.

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Volcanic eruption effects on temperate and boreal tree growth

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  1. Volcanic eruption effects on temperate and boreal tree growth Nir Y Krakauer1*, Nicole V Smith1, James T Randerson2 1. Geological and Planetary Sciences, Caltech 2. Earth Systems Science, UC Irvine * niryk@caltech.edu

  2. Motivation • Why did the atmospheric CO2 growth rate drop for 2 years after the 1991 Pinatubo eruption? • An enhanced carbon sink also followed the 1982 El Chichón and 1963 Agung eruptions

  3. How would eruptions lead to a carbon sink? • Roderick et al (2001) and Gu et al (2003): light scattering by aerosols boosts canopy photosynthesis for 1-2 years after eruptions • Jones and Cox (2001) and Lucht et al (2002): soil respiration is lower because of cooling; boreal photosynthesis might decrease Gu et al 2003 Lucht et al 2002

  4. What we did • What happened to tree ring widths after past eruptions? • Large eruptions since 1000 from ice core sulfate profiles • 40,000 ring width series from the International Tree Ring Data Bank (ITRDB) Crowley 2000

  5. Width changes by latitude

  6. above 45°N: by genus

  7. The 1990s: Harvard Forest

  8. Conclusions • Boreal trees had narrower rings up to 8 years after Pinatubo-size eruptions • Temperate-zone trees showed smaller effects. American trees has wider rings for 2 years after eruptions • From this sample, negative influences on NPP appear to dominate positive ones, at least in boreal forests

  9. Research directions • Are there tree groups that show large growth enhancements after eruptions (understory trees, moisture-stressed trees…)? • What’s the impact of eruptions on global NPP? • Can we tell what happens to trees’ physiology after eruptions (short growing season, nutrient stress…)? • Why are boreal rings narrower so long after eruptions?

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