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Progress in understanding carbon dynamics in primary forests CD08 team
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Stock (e.g. biomass, soil C) Input Output Mean Residence Time = Stock/Output How many of us model Carbon dynamics
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Stock (e.g. biomass, soil C) Input Output Mean Residence Time = Stock/Output How many of us model Carbon dynamics
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Input Output Mean Residence Time = Stock/Output NOT necessarily = Mean age of C in stocks The better model: Fast cycling components Slower cycling components
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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
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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?
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Measurement of tree diameter during establishment of permanent plot
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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
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Growth rates from dendrometer bands (Vieira et al., Oecologia 2004)
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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
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No Individuals/ ha Manaus SantarémRio Branco Trees can be old Extrapolating growth rates, we estimate >20% of all trees and 15-35% of trees 10-30 cm diameter are >300 yrs old Age of individuals estimated from diameter/growth rate (yr)
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Limited radiocarbon data available agree qualitatively with age structure based on Monte Carlo extrapolation of dendrometer growth rates % of individuals with age >300 years
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Trees 45years Basal age (years) from radiocarbon No of individuals
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Manaus Santarém Rio Branco Individuals/ha 626 460 466 Biomass C MgC/ha 180 141 95 Growth MgC/ha/yr 1.6-2.1 2.2 -3.0 3.3-3.4 Mean age of C (yr)* 260 220 240 MRT of C (stock/growth)** 114 74 53 * From monte carlo simulations **biomass-weighted Data from Vieira et al. 2004 C dynamics differ with forest location
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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
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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:
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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
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