Progress in understanding carbon dynamics in primary forests CD08 team

Stock (e.g. biomass, soil C) Input Output Mean Residence Time = Stock/Output How many of us model Carbon dynamics

Stock (e.g. biomass, soil C) Input Output Mean Residence Time = Stock/Output How many of us model Carbon dynamics

Input Output Mean Residence Time = Stock/Output NOT necessarily = Mean age of C in stocks The better model: Fast cycling components Slower cycling components

14 C atmosphere atmosphere, lagged 3 years 0-5 cm, Surface litter 0-5 cm soil Modeling turnover time using changes in bomb radiocarbon Requires C to have both rapidly and slowly cycling components; Like trees, soils cannot be modeled as single homogeneous C pools

Trees How old are tropical trees? How fast do they grow? How long do they store carbon? How do characteristics vary across the Amazon basin?

Measurement of tree diameter during establishment of permanent plot

Rio Branco Manaus Santarém Field sites All terra firme forest Soils are Oxisols Variation in dry season length: Shortest in Manaus, longer in Rio Branco, Santarém Paragominas

Growth rates from dendrometer bands (Vieira et al., Oecologia 2004)

Radiocarbon and dendrometers agree Trees grow slowly 10-30cm 30-50cm >50cm Manaus Rio Branco Santarém Little trees grow slower than big trees Trees in Manaus grow ~2x slower than other areas

No Individuals/ ha Manaus SantarémRio Branco Trees can be old Extrapolating growth rates, we estimate >20% of all trees and 15-35% of trees cm diameter are >300 yrs old Age of individuals estimated from diameter/growth rate (yr)

Limited radiocarbon data available agree qualitatively with age structure based on Monte Carlo extrapolation of dendrometer growth rates % of individuals with age >300 years

Trees 45years Basal age (years) from radiocarbon No of individuals

Manaus Santarém Rio Branco Individuals/ha Biomass C MgC/ha Growth MgC/ha/yr Mean age of C (yr)* MRT of C (stock/growth)** * From monte carlo simulations **biomass-weighted Data from Vieira et al C dynamics differ with forest location

How can MRT of C in wood be less than the mean age of C in standing wood? Standing stock (180 MgC/ha) Mean age ~260 yr Growth ~2 MgC/ha/yr Mortality ~2 MgC/ha/yr Mean age C ~90 yr Probability of mortality is not the same for all trees – younger, or faster growing, trees tend to die more frequently Need better understanding of what causes tree mortality

Low carbon use efficiency (NPP/GPP ~ 30% at Manaus and Santarém sites) ~25% of NPP used for wood growth at Manaus (data pending for other sites) Although biomass may recover quickly through fast-growing pioneer species, slow growing species (therefore biodiversity) will take centuries to recover from disturbance Implications of low growth rates:

Conclusions: Models of forest dynamics need to account for: Heterogeneity of C in wood and soil pools (age of standing stock > age of C in dying wood; age of C in soils> age of C respired) Low allocation of C to wood growth Differences in wood dynamics and forest structure across the Amazon basin