Measuring in-canopy advection of carbon dioxide using a new transect measurement system (TRAM)

An imbalance often is seen over forests between estimates of net ecosystem exchange (NEE) of carbon from above-canopy eddy-correlation flux measurements and other methods. One hypothesis is that nocturnal emission of carbon dioxide from soils preferentially builds up in low-lying

areas and drains to locations not sampled by the above-canopy sensors. To investigate this hypothesis, we developed an instrument platform that carries a carbon dioxide sensor and a sonic anemometer along a path through a forest canopy. The platform operates like a toy electric train, with a motorized set of wheels driving along a track. The track consists of a sequence of cables suspended from towers that forms a closed circuit. We show results from the first use of this system along a 220m transect sampling at the bottom and middle of the canopy at the University of Colorado's

Flux Facility CUFF in an alpine forest at Niwot Ridge.