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

Carbon Release from Stems and Branches in a Seasonally Flooded Amazon ForestViviana Horna 1,2) and Reiner Zimmermann 1,2)1) Max Planck Institute for Biogeochemistry, Carl Zeiss Promenade 10, D-07701 JenaGermany2) Forest Ecology and Remote Sensing Group, Ecological-Botanical Gardens, Universityof Bayreuth, D-95440 Bayreuth, Germanyvhorna@bgc-jena.mpg.de Phone: ++49-3641-686731 Fax: ++49-3641-686710Release of CO 2 from woody tree tissue was measured in eight major tree species of a centralAmazonian “Varzea” white water inundation forest. Varzea forests are believed to have a highcarbon release since net wood productivity is low in spite of favorable nutrient supply andclimate. Consecutive daily courses of carbon release were measured starting in March 1999,using stem and branch chambers in an open system with an integrated infrared gas analyzerrunning in differential mode. Deciduous tree species (Albizia multiflora, Tabebuia barbata,Pseudobombax munguba, Crataeva benthamii, Vitex cymosa) and evergreen tree species(Nectandra amazonum, Laetia corymbulosa, Pouteria glomerata) were compared. The resultswere analyzed for different flooding conditions of increasing water level (February-April),maximum water level (May-July), decreasing water level (August-October) and underconditions of no flooding (November-January).Trees showed maximum rates of woody tissue CO 2 release during early flooding and variedfrom 2 to 14 µmol CO 2 m -2 s -1 in the lower part of the main stem during the day. These valuesare higher than those reported in the literature for broad-leaved species. The highest values ofcarbon release were observed in the main stem of the evergreen Nectandra amazonum. Forthe remaining seasons daily variation of main stem CO 2 release was smaller with a maximumof 4 µmol CO 2 m -2 s -1 between night and midday hours. CO 2 release rates in the upper stemwere rather constant throughout the year. Branch CO 2 release was high during new leafdevelopment indicating a tight relationship with leaf phenology.The up-scaled values of CO 2 release from above-ground woody parts per season showed alinear relationship with tree basal area: lowest correlation (r 2 =0.53) was found for the seasonof increasing water level and highest correlation (r 2 =0.68) during the season of decreasingwater level. Annual stand carbon release from above-ground tree woody biomass wasestimated to be 1870 g C ha -1 a -1 . This value is 5 to 6 times higher than stand carbon releasevalues reported for other non-flooded neotropical forest (Odum, 1970, Ryan et al. 1994, Meir1996).The results of this study support the hypothesis of a high respiration in seasonally floodedtropical forests. A close relationship exists between apparent carbon release in branches andtree leaf phenology.