Tree Growth and Ecosystem Respiration in a Central Amazon Forest

1. Tree Growth and Ecosystem Respiration in a Central Amazon Forest Jeffrey Q. Chambers, Edgard S. Tribuzy, Roseana P. da Silva, Ligia C. Toledo, Joaquim dos Santos, Niro Higuchi, and Susan E. Trumbore

2. Overview We are studying tree growth and respiration in Central Amazon forest near Manaus, Brazil. We are interested in understanding how physiological processes underlying ecological observations respond to environmental variability. We have also developed a stochastic-empirical model for exploring how environmental change affects ecosystem carbon balance. A MISR image of the central Amazon showing the meeting of the waters where the Rio Negro and Rio Solimões merge to form the Amazon river. The Ducke botanical reserve is the large undisturbed block of forest at the north of Manaus. See the Ikonos image below for a more detailed image of our primary study sites.

3. Precipitation Variability in Manaus from 1910-85 The Central Amazon experiences considerable intra- and inter-annual variability in precipitation. Changes in moisture availability affects a number of physiological processes including growth and respiration. El Niño often results in a dry early wet season.

4. Seasonal Variability in Forest Wood Production Linear gauge data There is a steep increase in wood production at the onset of the rainy season. Using linear gauge tensiometers and TDR we are comparing stem volume changes associated with moisture with changes from actual growth. Daily shrinking and swelling associated with transpiration is small compared with growth. Production in the Central Amazon is not constant.

5. Spatial and Temporal Variation in Soil Respiration 1.70 3.04 3.47 3.10 2.76 2.53 2.60 2.10 3.21 Plateau 2.77 Slope Soil Respiration[Log(g C m-2 day-1)] 1.98 Valley There is considerable spatial and temporal variability in the soil respiratory flux. Numerical values indicate means in original flux units. Changes in soil moisture drives some of this variability. Much valley forest flux may actually be above-ground due to the dense root mat.

6. Temporal Variation in Woody Tissue Respiration Similar to soil respiration, stem respiration peaks in the early wet season and drops during the dry season. Because of the log-normal distribution and high variability (A), the cumulative flux must be estimated using a randomization model (B).

7. Central Amazon Forest Ecosystem Respiration Result indicate seasonal variability in ecosystem respiration shown as the range of the total flux. The value for leaf respiration is preliminary and we have a study underway to quantify seasonal variability. We are also exploring mechanistic factors that explain this variability. Reco = 30.3 12.1 Rleaf 4.2 1.9 12.1 Rstem RCWD Rsoil Units: Mg C ha-1 yr-1 Ecosystem carbon use efficiency (CUE) about 25%.

8. Partitioning of NPP in Central Amazon Forest To quantify how carbon storage responds to an increase in productivity both the allocation of net primary production (NPP) ... Woody tissues represent 49% of above-ground NPP

9. Carbon Pools in Central Amazon Forest and the size of the carbon reservoir determines the residence time and the capacity for sequestering carbon. Only large wood and SOM have a high capacity to sequester carbon for long periods of time.

10. 20 m We have developed a stochastic-empirical individual-based model to explore the carbon cycling dynamics of large wood in Central Amazon forest. Tree Stand Plot

11. Carbon cycling structure of the model CO2 CO2 respiration growth mortality live wood coarse litter fragmentation recruitment total large wood (TLW) We can use this model to explore how changes affecting individual trees and canopy gaps influences ecosystem scale carbon cycling and storage.

12. Carbon Balance and Catastrophic Mortality Points above the zero line indicate TLW is a carbon sink, and below the line TLW is a carbon source. TLW can act as a carbon sink by and increase in production and/or a decrease in coarse litter respiration. There is a quick and large loss of ecosystem carbon immediately following a large mortality event. Afterwards large wood primarily acts as a small sink for many decades. 100 ha run only background mortality TLW carbon balance (Mg C ha-1 yr-1) 20% mortality events

13. IKONOS image of 10x10 km area in the Central Amazon High resolution satellite imagery is useful for quantifying the frequency and extent of catastrophic mortality events such as this blowdown which can exceed 2,000 ha in size. The Jacaranda plots are indicated with gray lines. 400 m Severe downburst type winds are associated with late dry season storms.

14. The carbon sequestration potential of large wood We can also use the model to explore how large wood carbon balance responds to an increase in NPP. NPP was increased 0.5% per year for fifty years (the gray area). Large wood sequestered carbon for many years but at a low annual rate. The annual sink (0.5 Mg C ha-1 yr-1) is much lower than estimates from eddy covariance tower studies.

15. Conclusions • Soil and stem respiration increase during the dry to wet season transition and there is a comparable increase in tree growth during these transition months. • Total ecosystem respiratory flux is not a constant and varies seasonally. • The frequency and extent of catastrophic mortality is important for understanding forest carbon balance. • Only large wood and SOM can sequester significant amounts of carbon in response to an increase in NPP. • Central Amazon forests can sequester a large amount of carbon with increasing NPP, but in any given year sequestration is limited to about 0.5-1.0 Mg C ha-1 yr-1. For further information and reprints contact Jeff Chambers at chambersjq@yahoo.com