Using FLUXNET data to improve models of springtime vegetation activity onset in forest ecosystems
Melaas, E. ; Richardson, A. ; Friedl, M. ; Dragoni, D. ; Gough, C. ; Herbst, M. ; Montagnani, L. ; Moors, E.J. - \ 2013
Agricultural and Forest Meteorology 171-172 (2013). - ISSN 0168-1923 - p. 46 - 56.
terrestrial biosphere model - deciduous forest - co2 exchange - temperate regions - soil-temperature - phenology model - carbon-dioxide - annual cycle - bud-burst - trees
Vegetation phenology is sensitive to climate change and variability, and is a first order control on the carbon budget of forest ecosystems. Robust representation of phenology is therefore needed to support model-based projections of how climate change will affect ecosystem function. A variety of models have been developed to predict species or site-specific phenology of trees. However, extension of these models to other sites or species has proven difficult. Using meteorological and eddy covariance data for 29 forest sites (encompassing 173 site-years), we evaluated the accuracy with which 11 different models were able to simulate, as a function of air temperature and photoperiod, spatial and temporal variability in the onset of spring photosynthetic activity. In parallel, we also evaluated the accuracy with which dynamics in remotely sensed vegetation indices from MODIS captured the timing of spring onset. To do this, we used a subset of sites in the FLUXNET La Thuile database located in evergreen needleleaf and deciduous broadleaf forests with distinct active and dormant seasons and where temperature is the primary driver of seasonality. As part of this analysis we evaluated predictions from refined versions of the 11 original models that include parameterizations for geographic variation in both thermal and photoperiod constraints on phenology. Results from cross-validation analysis show that the refined models predict the onset of spring photosynthetic activity with significantly higher accuracy than the original models. Estimates for the timing of spring onset from MODIS were highly correlated with the onset of photosynthesis derived from flux measurements, but were biased late for needleleaf sites. Our results demonstrate that simple phenology models can be used to predict the timing of spring photosynthetic onset both across sites and across years at individual sites. By extension, these models provide an improved basis for predicting how the phenology and carbon budgets of temperature-limited forest ecosystems may change in the coming decades.
Severe anaemia in Malawian children
Calis, J.C.J. ; Phiri, K.S. ; Faragher, E.B. ; Brabin, B.J. ; Bates, I. ; Cuevas, L.E. ; Haan, R.J. de; Phiri, A.I. ; Malange, P. ; Khoka, M. ; Hulshof, P.J.M. ; Lieshout, L. ; Beld, M.G.H.M. ; Teo, Y.Y. ; Rockett, K.A. ; Richardson, A. ; Kwiatkowski, D.P. ; Molyneux, M.E. ; Hensbroek, M.B. van - \ 2008
In: Aetiology, Pathogenesis & Consequences of Severe Anaemia in Malawian Children: HIV and other factors Amsterdam : Buijten & Schipperheijn - ISBN 9789090228860 - p. 31 - 47.
Comparison of different objective functions for parameterization of simple respiration models
Wijk, M.T. van; Putten, B. van; Hollinger, D. ; Richardson, A. - \ 2008
Journal of Geophysical Research: Biogeosciences 113 (2008). - ISSN 2169-8953
net ecosystem exchange - eddy covariance data - water-vapor exchange - carbon-dioxide - primary productivity - co2 exchange - forest - fluxes - uncertainty - optimization
The eddy covariance measurements of carbon dioxide fluxes collected around the world offer a rich source for detailed data analysis. Simple, aggregated models are attractive tools for gap filling, budget calculation, and upscaling in space and time. Key in the application of these models is their parameterization and a robust estimate of the uncertainty and reliability of their predictions. In this study we compared the use of ordinary least squares (OLS) and weighted absolute deviations (WAD, which is the objective function yielding maximum likelihood parameter estimates with a double exponential error distribution) as objective functions within the annual parameterization of two respiration models: the Q10 model and the Lloyd and Taylor model. We introduce a new parameterization method based on two nonparametric tests in which model deviation (Wilcoxon test) and residual trend analyses (Spearman test) are combined. A data set of 9 years of flux measurements was used for this study. The analysis showed that the choice of the objective function is crucial, resulting in differences in the estimated annual respiration budget of up to 40%. The objective function should be tested thoroughly to determine whether it is appropriate for the application for which the model will be used. If simple models are used to estimate a respiration budget, a trend test is essential to achieve unbiased estimates over the year. The analyses also showed that the parameters of the Lloyd and Taylor model are highly correlated and difficult to determine precisely, thereby limiting the physiological interpretability of the parameters
Severe Anemia in Malawian Children
Calis, J.C.J. ; Kamija, S.P. ; Faragher, E.B. ; Brabin, B.J. ; Bates, I. ; Cuevas, L.E. ; Haan, R.J. de; Phiri, A.I. ; Malange, P. ; Khoka, M. ; Hulshof, P.J.M. ; Lieshout, L. ; Beld, M.G.H.M. ; Teo, Y.Y. ; Rockett, K.A. ; Richardson, A. ; Kwiatkowski, D.P. ; Molyneux, M.E. ; Hensbroek, M.B. van - \ 2008
New England Journal of Medicine 358 (2008)9. - ISSN 0028-4793 - p. 888 - 899.
vitamin-a supplementation - young-children - severe malaria - salmonella bacteremia - plasmodium-falciparum - ancylostoma-duodenale - necator-americanus - blood-transfusion - northern ghana - iron status
Background Severe anemia is a major cause of sickness and death in African children, yet the causes of anemia in this population have been inadequately studied. Methods We conducted a case¿control study of 381 preschool children with severe anemia (hemoglobin concentration,
CO2 balance of boreal, temperate, and tropical forests
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. ; Beers, C. van; 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. ; Maire, G. Le; 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. ; Janssens, I.A. - \ 2007
Global Change Biology 13 (2007)12. - ISSN 1354-1013 - p. 2509 - 2537.
net primary production - carbon-dioxide exchange - total soil respiration - eddy-covariance measurements - water-vapor exchange - black spruce forests - ponderosa pine forests - amazonian rain-forest - broad-leaved forest - gross primary production
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.