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The Effect of Canopy Gaps on Subcanopy Ventilation and Scalar Fluxes above a Tropical Forest

Scott Miller, SUNY Albany, smiller@albany.edu (Presenting)
Mike Goulden, UC Irvine, mgoulden@uci.edu
Humberto Rocha, University of Sao Paulo, humberto@model.iag.usp.br

Forest gaps may provide conduits that preferentially vent moist, CO2 rich subcanopy air to the atmosphere. We measured the above-canopy fluxes of sensible heat, CO2, and water vapor, and vertical profiles of CO2 and water vapor, from two 67-m towers in a selectively-logged Brazilian rainforest as part of the Large-Scale Biosphere Atmosphere Experiment in Amazonia (LBA). One tower was in an intact patch of forest within the selectively logged area; the other was 400 m upwind in a large gap created by the logging. The logging removed ~3.5 trees ha-1, and increased the incidence of gaps by a factor of 3 over nearby undisturbed forest. The forest understory was drier and warmer during daytime after the logging, which would be expected to increase flammability. After the logging, the daytime subcanopy air in the intact patch of forest had more CO2, more water vapor, and was cooler than the air at comparable altitudes in the gap. Meanwhile, the daytime CO2 flux was less negative (reduced CO2 uptake) above the gap than above the intact forest, the daytime evapotranspiration was greater above the gap than the intact forest, and the daytime sensible heat flux was lower above the gap than the intact forest. These patterns cannot be explained fully by the local loss of canopy gas exchange in the gap, but are consistent with the horizontal transport into the gap, and subsequent vertical transport out of the gap, of high-CO2, humid, cool air from the forest understory. Estimates of the CO2 venting flux indicate the potential for high rates of subcanopy scalar emissions out the gap; however, these estimates were uncertain because the contribution of the gap to the flux footprint was not known. Further measurement and modeling efforts are needed to better understand the effect of canopy gaps on flux footprints.

Presentation Type:  Poster

Abstract ID: 42

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