A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Seasonality of Stem Respiration at the Tapajos National ForestEvilene Lopes 1 , Patrick Crill 1 , Michael Keller 1,2 , Rosenildes Guimaraes 3 and WilleyMachado 41 Complex System Research Center, Morse Hall, University of New Hampshire, Durham,NH 03824, USA2 USDA Forest Service, International Institute of Tropical Forestry, Rio Piedras, PuertoRico3Desenvolvimento Regional RHAE/LBA4Iniciacao cientifica CNPq/LBAEmail addresses: evilene@kaos.sr.unh.edu, patrick.crill@unh.edu,michael.keller@unh.edu, roguisan@bol.com.br, willmach@zipmail.com.brStem respiration is one of the four major components of ecosystem respiration inthe forest environment. Previous studies in temperate and boreal forest have estimatedthat stem respiration contributes only 5% of ecosystem respiration. Based on recentestimates of ecosystem respiration from eddy covariance flux measurements and soilrespiration from chambers at the Tapajos National Forest (TNF), Para State, Brazil, itappears that soils emit less CO 2 than expected. The remaining CO 2 emission must befrom foliage, live and dead wood respiration. We have been measuring stem respirationmanually and discontinuously at the TNF since July 2002 and bi-weekly since November2001 at two sites at TNF. CO 2 is measured using an infrared gas analyzer (LI-6251). Bothsites have towers, which continuously measure NEE by eddy covariance and soilrespiration by an automatic chamber system. The undisturbed forest site is located nearthe km 67 of the BR-163 (Cuiaba-Santarem Highway). The logged forest site is locatednear the km 83 of the same road. At km 83, the forest was selectively logged betweenAugust 2001 and January 2002. Stem respiration fluxes varied between 0.11 and 3.95µmol CO 2 m -2 s -1 , with an average of 1.2 (+ 0.81) µmol CO 2 m -2 s -1 . The fluxes at thelogged site increased with increasing precipitation at the beginning of 2002 while theopposite trend was observed at the undisturbed site.