1. 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 niryk@caltech.edu

2. Motivation  Why did the atmospheric CO 2 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

9. The 1990s: Harvard Forest

10. 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

11. 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?