Mechanistic model for light-controlled phenology - its implication on the seasonality of water and carbon fluxes in the Amazon rainforests Yeonjoo Kim Lucy Hutyra, Marcos Longo, Ryan Knox, David Medvigy, Steven Wofsy, Rafael Bras and Paul Moorcroft Harvard University

Outline Backgrounds Models Seasonality Summary

Motivation Betts et al. (2004) Saleska et al. (2007) Amazon rainforests dieback Betts et al. (2004) Saleska et al. (2007)

Net Carbon Fluxes to the atmosphere Modeling Net Carbon Fluxes to the atmosphere (KM67) Photosynthesis > Respiration Latent Heat Flux (Reserva Jaru) Saleska et al. (2003) Wang and Zhe (2007)

Observation Myneni et al. (2007) Regional average in the forests Monthly maximum of hourly Shortwave Radiation (W/m2) Leaf Area Index (m2/m2) Myneni et al. (2007) Observation in the forest at Santarem (KM67)

Ecosystem Demography Model (ED2) Moorcroft et al. (2001) & Medvigy et al. (2008) Traditional ‘big leaf’ model v.s. Age and Size structured model

Mechanistic Light-controlled Phenology model Photosynthetic Capacity

Model fitting with Observations Ecosystem measurements at KM67 site (3 deg W and 55 deg S) Ecosystem structure & composition NEE - diurnal & nocturnal Litter Growth & Mortality → ED model parameters to be constrained with measurements! - phenology, respiration, and growth/mortality Flux tower Forest Inventory

Seasonal Dynamics Soil depth - shallow (1m) v.s. deep (6m)  Observation --- Initial model - shallow — Initial model - deep — Fitted model - deep Soil depth - shallow (1m) v.s. deep (6m) Model fitting

Seasonal Carbon Dynamics - NEE=R-GPP Not directly fitted to GPP and R Light-controlled phenology Moisture dependency in soil respiration  Observation — Initial model — Fitted model  Observation — Initial model — Fitted model

Seasonal Carbon Dynamics It is necessary to have a light-controlled phenology to have a right seasonality of GPP.  Observation — Initial model --- Initial model with an adjusted optimal soil moisture — Fitted model

Seasonal Leaf Dynamics  Observation — Initial model — Fitted model Model fitting LAI not used for fitting observation: 1km MODIS LAI  Observation — Initial model — Fitted model

Annaul Ecosystem Dynamics  Observation — Initial model — Fitted model  Observation — Initial model — Fitted model Growth and Mortality - DBH measurements in 2001 and 2005

Concluding Remarks The seasonality of ET can be captured with preventing the water stress during the dry season (e.g., deep soil). Observations suggests that the decrease in NEE during the dry season reflects the increase in GPP and the decrease in Respiration (NEE=R-GPP). The mechanistic light-controlled phenology model successfully captures the observed increase in productivity during the dry season. The seasonality of respiration can be captured with adjusting the optimal soil moisture for the soil respiration. The constrained model is capable of predicting both the fast-time scale fluxes and the slow-time scale ecosystem dynamics reasonably. Our studies on the impact of deforestation in the regional climate using ED2-BRAMS by Longo et al. will be presented at 11:25am in the parallel session in Smauma room.