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4 results on '"Hutyra, L.R."'

2. Modeling the carbon balance of Amazonian rain forests; resolving ecological controls on net ecosystem productivity

Author

Grant, R.F., Hutyra, L.R., De Oliveira, R.C., Munger, J.W., Saleska, S.R., and Wofsy, S.C.

Subjects
Rain and rainfall -- Analysis, Rain and rainfall -- Models, Rain and rainfall -- Chemical properties, Old growth forests -- Analysis, Old growth forests -- Models, Old growth forests -- Chemical properties, Ecology -- Analysis, Ecology -- Models, Ecology -- Chemical properties, Southern oscillation -- Analysis, Southern oscillation -- Models, Southern oscillation -- Chemical properties, Ecosystems -- Analysis, Ecosystems -- Models, Ecosystems -- Chemical properties, Rain forests -- Analysis, Rain forests -- Models, Rain forests -- Chemical properties, Biological sciences, Environmental issues
Abstract

There is still much uncertainty about ecological controls on the rate and direction of net C[O.sub.2] exchange by tropical rain forests, in spite of their importance to global C cycling. These controls are thought to arise from hydrologic and nutrient constraints to C[O.sub.2] fixation caused by seasonality of precipitation and adverse chemical properties of some major tropical soil types. Using the ecosystem model ecosys, we show that water uptake to a depth of 8 m avoids constraints to C[O.sub.2] and energy exchange from soil drying during five-month dry seasons typical for eastern Amazonian forests. This avoidance in the model was tested with eddy covariance (EC) measurements of C[O.sub.2] and energy fluxes during 2003 and 2004 over an old-growth forest on an acidic, nutrient-poor oxisol in the Tapajds National Forest (TNF) in Para, Brazil. Modeled C[O.sub.2] fixation was strongly constrained by slow phosphorus (P) uptake caused by low soil pH. Daytime C[O.sub.2] influxes in the model were in close agreement with EC measurements ([R.sup.2] > 0.8) during both wet and dry seasons. Both modeled and measured fluxes indicated that seasonality of precipitation affected C[O.sub.2] and energy exchange more through its effect on radiation and air temperature than on soil water content. When aggregated to a yearly scale, modeled and gap-filled EC C[O.sub.2] fluxes indicated that old-growth forest stands in the TNF remained within 100 g C*[m.sup.-2]*[yr.sup.-1] of C neutrality in the absence of major disturbance. Annual C transformations in ecosys were further corroborated by extensive biometric measurements taken in the TNF and elsewhere in the Amazon basin, which also indicated that old-growth forests were either small C sources or small C sinks. Long-term model runs suggested that rain forests could be substantial C sinks for several decades while regenerating after stand-replacing disturbances, but would gradually decline toward C neutrality thereafter. The time course of net ecosystem productivity (NEP) in the model depended upon annual rates of herbivory and tree mortality, which were based on site observations as affected by weather (e.g., El Nino Southern Oscillation [ENSO] events). This dependence suggests that rain forest NEP is strongly controlled by disturbance as well as by weather. Key words: Brazil; C[O.sub.2] exchange; disturbance; ecosys; ecosystem modeling; Her ecosystem productivity; rain forest.

Published
2009

4. CO2 balance of boreal, temperate, and tropical forests

Author

Luyssaert, S., Inglima, I., Jungs, M., Richardson, A., Reichsteins, M., Papale, D., Piao, S.L., Schulzes, E.D., Wingate, L., Matteucci, G., Aragaoss, L., Aubinet, M., van Beers, C., Bernhofer, C., Black, K.G., Bonal, D., Bonnefonds, J.M., Chambers, J., Ciais, P., Cook, B., Davis, K.J., Dolman, A.J., Gielen, B., Goulden, M., Grace, J., Granier, A., Grelle, A., Griffis, T., Grunwald, T., Guidolotti, G., Hanson, P.J., Harding, R., Hollinger, D.Y., Hutyra, L.R., Kolari, P., Kruijt, B., Kutsch, W., Lagergren, F., Laurila, T., Law, B.E., Le Maire, G., Lindroth, A., Loustau, D., Malhi, Y., Mateus, J., Migliavacca, M., Misson, L., Montagnani, L., Moncrief, J., Moors, E.J., Munger, J.W., Nikinmaa, E., Ollinger, S.V., Pita, G., Rebmann, C., Roupsard, O., Saigusa, N., Sanz, M.J., Seufert, G., Sierra, C., Smith, M., Tang, J., Valentini, R., Vesala, T., and Janssens, I.A.

Subjects
carbon-dioxide exchange, net primary production, black spruce forests, gross primary production, ponderosa pine forests, amazonian rain-forest, water-vapor exchange, broad-leaved forest, Alterra - Centre for Water and Climate, Wageningen Environmental Research, eddy-covariance measurements, Alterra - Centrum Water en Klimaat, total soil respiration
Abstract

Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 °C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for.

Published
2007

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