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Potential Net Primary Productivity in South America: Application of a Global Model
Ecological Applications (1991)
  • James W. Raich, Marine Biological Laboratory
  • E. B. Rastetter, Marine Biological Laboratory
  • J. M. Melillo, Marine Biological Laboratory
  • D. W. Kicklighter, Marine Biological Laboratory
  • P. A. Steudler, Marine Biological Laboratory
  • B. J. Peterson, Marine Biological Laboratory
  • A. L. Grace, University of New Hampshire, Durham
  • B. Moore III, University of New Hampshire, Durham
  • C. J. Vorosmarty, University of New Hampshire, Durham
Abstract
We use  a  mechanistically based ecosystem simulation model to  describe and analyze the spatial and temporal patterns of terrestrial net primary productivity (NPP) in South America. The Terrestrial Ecosystem Model (TEM) is designed to predict major carbon and nitrogen fluxes and pool sizes in terrestrial ecosystems at continental to global scales. Information from intensively studied field  sites is  used in combination with con-tinental-scale information on climate,  soils, and vegetation to estimate NPP in each of 5888 non-wetland, 0.5° latitude  x  0.5° longitude grid cells in South America, at monthly time steps.  Preliminary  analyses  are  presented  for the scenario of natural  vegetation throughout the continent, as a  prelude to evaluating human impacts on terrestrial NPP. The potential annual NPP of South America is estimated to be  12.5  Pglyr of carbon (26.3 Pglyr of organic matter) in a  non-wetland area of 17.0  x  106 km2• More than 50% of this production occurs in the tropical and subtropical evergreen  forest  region.  Six  in-dependent model runs, each based on an independently derived set of model parameters, generated mean annual NPP estimates for the tropical evergreen forest region ranging from 900 to 1510 g·m-2·yr-1 of carbon, with an overall mean of 1170 g·m-2·yr-1• Coefficients of variation in estimated annual NPP averaged 20% for any specific location in the evergreen forests, which is probably within the confidence limits of extant NPP measurements. Predicted  rates of mean annual NPP in other types of vegetation  ranged  from  95 g·m-2·yr-1 in arid shrublands to 930 g·m-2·yr-1 in savannas, and were within the ranges measured in empirical  studies. The spatial  distribution of predicted NPP was  directly compared with  estimates made using the Miami model of Lieth (1975).  Overall, TEM predictions were セ@10% lower than those of the Miami model, but the two models agreed closely on the spatial patterns ofNPP in South America. Unlike previous models, however, TEM estimates NPP monthly, allowing for the evaluation of seasonal phenomena. This is an important step toward integration of ecosystem  models with  remotely sensed infor-mation, global climate models, and atmospheric transport models, all of which are evaluated at comparable spatial and temporal scales. Seasonal patterns of NPP in South America are correlated with moisture availability in most vegetation types, but are strongly influenced by seasonal differences in cloudiness in the tropical evergreen forests. On an annual basis, moisture availability was the factor that was correlated most strongly with annual NPP in South America, but differences were again observed among vegetation  types. These results  allow  for the investigation and analysis of climatic controls over NPP at continental scales, within and among vegetation types, and within years. Further model validation is  needed. Nevertheless, the ability to investigate NPP-environment interactions with a  high spatial and temporal resolution at continental scales should prove useful if not essential for rigorous analysis of the potential effects of global climate changes on terrestrial ecosystems. 
Keywords
  • carbon fluxes,
  • ecosystem simulation model,
  • geographic information system,
  • global model,
  • modelling,
  • net primary productivity,
  • net primary productivity-environment interactions,
  • South America,
  • spatial and temporal patterns
Publication Date
1991
DOI
10.2307/1941899
Publisher Statement
Copyright 1991 by  the Ecological Society of America
Citation Information
James W. Raich, E. B. Rastetter, J. M. Melillo, D. W. Kicklighter, et al.. "Potential Net Primary Productivity in South America: Application of a Global Model" Ecological Applications Vol. 1 Iss. 4 (1991) p. 399 - 429
Available at: http://works.bepress.com/jim_raich/14/