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Forest disturbance reduces stem CO2 efflux from trees in the central Amazon

Tuesday, 25 June 2013: 08:15
La Paz - B East (Herradura San Jose)
Norbert Kunert , Forest Management, Instituto Nacional de Pesquisas da Amaz˘nia, Brazil
Liliane M. Teixeira , Forest Management, Instituto Nacional de Pesquisas da Amaz˘nia, Brazil
Jeffrey Q. Chambers , Climate Sciences Department, Lawrence Berkeley National Laboratory
Niro Higuchi , Forest Management, Instituto Nacional de Pesquisas da Amaz˘nia, Brazil
Joaquim dos Santos , Forest Management, Instituto Nacional de Pesquisas da Amaz˘nia, Brazil
Susan Trumbore , Biogeochemical Processes, Max Planck for Biogeochemistry, Germany
Daniel Magnabosco Marra , Instituto Nacional de Pesquisas da Amaz˘nia, Brazil
Tropical forests are subject to continuous changes in their structure and composition. These changes have various drivers such as interactions between tree individuals and species as well as natural calamities. The response of forest communities to natural disturbance is relatively well studied whereas studies exploring the physiological response of individual trees are still rare. Here, we present stem CO2 efflux data measured on trees exposed to different forest disturbance scenarios. The study was conducted in a terra firme forest close to Manaus over a five year period (January 2006 to December 2011). In the first year, three one hectare plots were set up and a full inventory including trees >10 cm (DBH) was conducted. Sixteen trees were selected in each plot.  Sample trees were equipped with dendrometer bands. Growth and stem CO2 efflux (portable closed dynamic chamber system) were measured montly. A natural forest disturbance was simulated at the beginning of the second year by selectively logging trees in two plots. Five trees were logged in one plot and 10 trees in another.  The third plot was left as a control. Growth and stem CO2 efflux was monitored monthly for one year after disturbance and the third year after disturbance. The sample trees in all plots showed similar relationships between CO2 efflux and growth before the logging. Changes in this relationship could be observed for trees growing on the plot with the heavy disturbance. The lower logging intensity did not significantly influence CO2efflux rates. Growth and maintenance respiration coefficients declined with higher disturbance rates indicating higher carbon use efficiency in the highly disturbed plots.

We assume that the reduced growth respiration in the highly disturbed stands is due to an enhanced internal transport of dissolved CO2 by an increased transpiration stream resulting out of changes in the canopy roughness.