Abstract ID: 64

Comprehensive assessment of carbon productivity, allocation and storage in three Amazonian forests

The allocation and cycling of carbon within forests is an important component of the biospheric carbon cycle, but is particularly understudied within tropical forests. Here we synthesise reported and unpublished results from three lowland rainforest sites in Amazonia (in the regions of Manaus, Tapajós and Caxiuanã), all major sites of the Large-Scale Biosphere-Atmosphere Programme (LBA). We attempt a comprehensive synthesis of the carbon stocks, nutrient status and particularly the allocation and internal carbon dynamics of all three sites. The calculated net primary productivities (NPP) are 10.1±1.4 (Manaus), 14.4±1.3 (Tapajós) and 10.0±1.2 (Caxiuanã) Mg C ha-1 a-1 the significantly higher values at Tapajós may be because of post-disturbance status or slightly higher soil fertility. All errors bars report standard errors. Soil and leaf nutrient analyses indicate that Tapajós has significantly more plant-available phosphorus and calcium. Autotrophic respiration at all three sites (14.9-24.4 Mg C ha a-1) is more challenging to measure, with the largest component and greatest source of uncertainty being leaf dark respiration. Comparison of measured soil respiration with that predicted from carbon cycling measurements provides an independent constraint. It shows general good agreement at all three sites, with perhaps some evidence for measured soil respiration being less than expected. 20-30% of fixed carbon is allocated below-ground. Comparison of gross primary productivity, GPP, derived from ecosystem flux measurements with that derived from component studies (NPP plus autotrophic respiration) provides an additional cross-check. The two approaches are in good agreement, giving increased confidence in both approaches to estimating GPP. The ecosystem carbon use efficiencies (CUEs) are similar at Manaus (0.34±0.10) and Caxiuanã (0.29±0.06), but may be higher at Tapajós (0.49±0.16), although the difference is not significant. Old-growth or infertile tropical forests may have low CUE compared to recently disturbed and/or fertile forests.

Session:  Carbon - Forest dynamics, natural disturbance, and recovery. (A)

Presentation Type:  Oral