Volcanic eruption effects on temperate and boreal tree

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 § 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

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

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

Width changes by latitude

above 45°N: by genus

The 1990 s: Harvard Forest

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

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?