We will combine radiocarbon with more traditional measures of C inventory and fluxes to
study the stocks, allocation and turnover of carbon at intensive study sites along the
eastern LBA transect. In spite of their importance to regional and global C budgets, the
understanding of C residence times in vegetation, detritus and soils is very poor in
tropical ecosystems. In particular, the roles of woody biomass and detritus, which contain
large amounts of C with decadal or longer turnover times, need to be better quantified and
are amenable to study with radiocarbon. We will focus on 5 specific components of
stand-level C cycling at several intensive study sites:
- quantifying of C uptake rates in growing trees using bomb radiocarbon in concert with
diameter increment measurements to determine the average rate (and variability) of tree
growth over the past 3 decades
- determining age demographics of tree populations, using radiocarbon to determine tree
- assessing the rate of production and decomposition of dead wood debris using permanent
plot and decomposition rate experiments
- using radiocarbon in fractionated organic matter together with measures of C fluxes and
stocks in soils to determine the amount and turnover time of C in fast-cycling and
mineral-stabilized organic matter in soils
- Using 14C measurements in respired CO2, microbial biomass, and
soil organic matter to partition total soil CO2 efflux into components from
metabolic respiration and heterotrophic decomposition.
We will combine these with measurements of litterfall, root dynamics and CO2
fluxes by other groups to produce site-specific models of C cycling for comparison with
eddy correlation measurements of net ecosystem production (NEP).
Our data will provide process-level understanding needed to apportion eddy correlation
measurements of whole-canopy net CO2 flux into above- and below- ground
components and to predict what factors may cause inter-annual variability in net C
balance. Our studies of tree age demographics will scale this understanding to larger
areas, and help determine the best way to extrapolate NEP measurements in space and in
time. At the global scale, our measurements of the time lag between C uptake by
photosynthesis and loss by decomposition are needed to test ecosystem C models.
Additionally, our work with tree demographics will have implications for forestry
management, since our preliminary results show some large, economically valuable trees are
very old (1000 years).