Right above the tree tops -- where most people might think there is just air -- Prof. Dan Yakir sees a distinctive atmospheric layer in which all sorts of complex exchanges are taking place. CO2, of course, is one of the important ones, and we still don’t understand all of the ins and outs of its flux through the forest, soil and atmosphere. Moisture, heat (and by extension light) and oxygen all cycle through the interface between the forest canopy and the lower atmosphere, as do a number of volatile organic compounds (VOCs) released by many trees. These compounds may contribute to the nucleation of water droplets in clouds – so that trees actually help create their own weather.
Last time we wrote about Yakir and his team, it was to showcase the Biosphere-Atmosphere Mobile Research Lab, a 12-ton truck carrying a telescopic mast that extends 28 meters straight up, enabling them to get monitoring equipment to that unique layer just above the canopy and to move it from forest to forest. In the past couple of years, research in this lab has been yielding some of the hard data needed to create accurate models of these flux phenomena.
That truck is now the center of a somewhat unusual international collaboration. Groups from the National Center for Atmospheric Research, Colorado (NCAR), and universities in Indiana, Germany and Spain are all converging on Israel for a two-part working conference called BRITE (for Bioregional Research along an Israeli TranEct). The great thing about this project, says Yakir, is that it grew out of some casual brainstorming: “It began as discussion between me and Alex Gunter of NCAR, and it was completely ad hoc. We didn’t wait to get funding; we just planned it and made it happen.”
The idea is a bit like a pot-luck dinner: Each of the “guests” brings something to the table – in this case hefty scientific equipment, some of it shipped halfway around the world. Each of the courses is meant to be a part of a complete “meal” – an attempt to fully understand the cycles in which VOCs are released into the atmosphere and affect the weather.
So one group is measuring the vegetation on the ground, another is looking at the chemistry of the VOCs in the layer near the canopy, a third checks the sizes of particles in the atmosphere, etc. Yakir’s group has a nifty piece of equipment with a sci-fi name – a quantum cascade laser -- which was made especially for them. They use it to measure a compound called COS, which exists in the atmosphere in parts per trillion. It turns out that once you can measure these minute amounts, COS is a good proxy for CO2 uptake. CO2 uptake has been very hard to measure directly, because forests release CO2 back into the atmosphere even as they absorb it, so most researchers end up measuring the net difference. COS, in contrast, is chemically converted in the plants, so it is only absorbed, not release.
Also online this week:
The latest in organic-inorganic interface research