Ecological Modelling, Vol 44 - n°1-2. Bias in estimates of primary production : an analytical solution / O.E. Sala (1988)

Public ISBD Titre de série : Ecological Modelling, Vol 44 - n°1-2 Titre : Bias in estimates of primary production : an analytical solution Type de document : texte imprimé Auteurs : O.E. Sala, Auteur ; M.E. Biondini, Auteur ; W.K. Lauenroth, Auteur Année de publication : 1988 Importance : pp. 43-55 Présentation : réf. Langues : Anglais (eng) Résumé : This paper addresses the issue of the effect of random error upon the estimates of above-or belowground net primary production (NPP). We show that ramdom errors in estimates of biomass do not compensate but always result in a positive bias in estimates of NPP. Second, we demonstrate that the larger the number of time intervals considered, the higher is the positive bias or overestimation error. An effect similar to an increase in the number of sampling periods is obtained by increasing the number of components utilized in estimating NPP. These are usually taxonomic or functional (depth, live, recent dead, etc.) components. We calculate the magnitude of the overestimation error as a function of the size of the difference in two sequential estimates of biomass and the variability associated with them. We propose a method that uses this error to correct the estimates of NPP for the positive bias resulting from random errors and to develop confidence intervals for the corrected NPP. We suggest that this method will remove the positive bias from estimates of NPP upon which nutrient budgets, energy flow and trophic webs rely. The concepts presented will help in the design of experiments that use production as a response variable. Type de document : Tiré à part Permalien de la notice : https://infodoc.agroparistech.fr/index.php?lvl=notice_display&id=147544 Ecological Modelling, Vol 44 - n°1-2. Bias in estimates of primary production : an analytical solution [texte imprimé] / O.E. Sala, Auteur ; M.E. Biondini, Auteur ; W.K. Lauenroth, Auteur . - 1988 . - pp. 43-55 : réf. Langues : Anglais (eng) Résumé : This paper addresses the issue of the effect of random error upon the estimates of above-or belowground net primary production (NPP). We show that ramdom errors in estimates of biomass do not compensate but always result in a positive bias in estimates of NPP. Second, we demonstrate that the larger the number of time intervals considered, the higher is the positive bias or overestimation error. An effect similar to an increase in the number of sampling periods is obtained by increasing the number of components utilized in estimating NPP. These are usually taxonomic or functional (depth, live, recent dead, etc.) components. We calculate the magnitude of the overestimation error as a function of the size of the difference in two sequential estimates of biomass and the variability associated with them. We propose a method that uses this error to correct the estimates of NPP for the positive bias resulting from random errors and to develop confidence intervals for the corrected NPP. We suggest that this method will remove the positive bias from estimates of NPP upon which nutrient budgets, energy flow and trophic webs rely. The concepts presented will help in the design of experiments that use production as a response variable. Type de document : Tiré à part Permalien de la notice : https://infodoc.agroparistech.fr/index.php?lvl=notice_display&id=147544

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Ecological Modelling, Vol 45 - n°4. Analysis of forest succession with fuzzy graph theory / D.W. Roberts (1989)

Public ISBD Titre de série : Ecological Modelling, Vol 45 - n°4 Titre : Analysis of forest succession with fuzzy graph theory Type de document : texte imprimé Auteurs : D.W. Roberts, Auteur Année de publication : 1989 Importance : pp. 261-274 Présentation : ill., tabl., réf. Langues : Anglais (eng) Catégories : Thésaurus Agrovoc Forêt ; Spermatophyta ; Prunus americana ; Quercus alba ; Quercus velutina ; Amérique du Nord Résumé : Fuzzy graph theory is a fuzzy set generalization of classical graph theory suitable for preliminary analysis of many ecological systems. Fuzzy graph theory is applicable to the analysis of any dynamical system where the values of all state variables are known at at least two points in time. This paper presents some methods and algorithms of fuzzy graph theory, and uses fuzzy graph theory in an analysis of the compositional dynamics of an oak woods in Wisconsin, U.S.A. Three fuzzy relations for succession are compared using the same data to determine how the depiction of forest dynamics depends upon the characteristics of the chosen relation. The inherent minimum requirements for recognizing succession vary with each relation, and the relations from a hierarchy of rigor in requirements. The fuzzy graphs show that the observed successional trends are dependent upon the characteristics of each relation. Fuzzy graph theory is then used to analyze the time-variance of the system dynamics by comparing fuzzy graphs of succession for four consecutive time periods. The analysis shows only small changes in the system dynamics with time, demonstrating that the system is not strongly time-varying. The rate of system change, however, appears to be slowing. Finally, fuzzy graph theory is compared to vector field methods of dynamical system analysis. Type de document : Tiré à part Permalien de la notice : https://infodoc.agroparistech.fr/index.php?lvl=notice_display&id=147895 Ecological Modelling, Vol 45 - n°4. Analysis of forest succession with fuzzy graph theory [texte imprimé] / D.W. Roberts, Auteur . - 1989 . - pp. 261-274 : ill., tabl., réf. Langues : Anglais (eng) Catégories : Thésaurus Agrovoc Forêt ; Spermatophyta ; Prunus americana ; Quercus alba ; Quercus velutina ; Amérique du Nord Résumé : Fuzzy graph theory is a fuzzy set generalization of classical graph theory suitable for preliminary analysis of many ecological systems. Fuzzy graph theory is applicable to the analysis of any dynamical system where the values of all state variables are known at at least two points in time. This paper presents some methods and algorithms of fuzzy graph theory, and uses fuzzy graph theory in an analysis of the compositional dynamics of an oak woods in Wisconsin, U.S.A. Three fuzzy relations for succession are compared using the same data to determine how the depiction of forest dynamics depends upon the characteristics of the chosen relation. The inherent minimum requirements for recognizing succession vary with each relation, and the relations from a hierarchy of rigor in requirements. The fuzzy graphs show that the observed successional trends are dependent upon the characteristics of each relation. Fuzzy graph theory is then used to analyze the time-variance of the system dynamics by comparing fuzzy graphs of succession for four consecutive time periods. The analysis shows only small changes in the system dynamics with time, demonstrating that the system is not strongly time-varying. The rate of system change, however, appears to be slowing. Finally, fuzzy graph theory is compared to vector field methods of dynamical system analysis. Type de document : Tiré à part Permalien de la notice : https://infodoc.agroparistech.fr/index.php?lvl=notice_display&id=147895

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Ecological Modelling, Vol 60 - n°1. Canopy photosynthesis and transpiration estimates using radiation interception models with different levels of detail / C.O. Stockle (1992)

Public ISBD Titre de série : Ecological Modelling, Vol 60 - n°1 Titre : Canopy photosynthesis and transpiration estimates using radiation interception models with different levels of detail Type de document : texte imprimé Auteurs : C.O. Stockle, Auteur Année de publication : 1992 Importance : pp. 31-44 Présentation : ill., graph., réf. Langues : Anglais (eng) Catégories : Thésaurus Agrovoc Photosynthèse ; Transpiration Résumé : To simulate radiation interception, the physical structure of plant canopies is defined by the inclination, orientation, and location of their foliage elements. Detailed models must consider all these factors, which has a significant impact on the required computation time. Simplifications of these models are possible, sacrificing accuracy for computation speed. An existing canopy radiation model was modified to incorporate an ellipsoidal distribution of foliage elements, which was continuous over the range of leaf angles and allowed for accommodation of horizontal or vertical tendencies of the canopy. The canopy was divided into thin layers, and the foliage elements within each layer were classified into nine leaf inclination and azimuth angle classes. Simplications of the model including options for varying the thickness of the canopy layers and the number of angle classes, for modeling the canopy as a single layer, and for partitioning the foliage elements in each layer into sunlit and shaded fractions, with disregard of leaf angle classes were also incorporated. This radiation model and its simplications were implemented in a computer simulation module for estimating canopy photosynthesis and transpiration. Simulation runs were performed for conditions with low and high leaf area index (lai) and irradiance. It was found that canopy photosynthesis and transpiration estimates, determined using canopy layer thickness of 0.5 lai and three inclination and azimuth angle classes, compared well (negligible error) with simulations using 0.1 lai and nine leaf angle classes, an standard recommendation for detailed models. If only photosynthesis estimates were of interest, even thicker layers could be used. Furthermore, errors were small if only average irradiance over sunlit and shaded leaf fractions by layer were considered, fluctuating from 0% to 4.3% for photosynthesis estimates, and from 0% to 2.7% for transpiration estimates. In many instances, a single layer divided into sunlit and shaded elements yielded reasonable results. Simplified canopy radiation models resulted in a dramatic decrease of computation time, up to View the MathML source of that required by the standard. Type de document : Tiré à part Permalien de la notice : https://infodoc.agroparistech.fr/index.php?lvl=notice_display&id=147554 Ecological Modelling, Vol 60 - n°1. Canopy photosynthesis and transpiration estimates using radiation interception models with different levels of detail [texte imprimé] / C.O. Stockle, Auteur . - 1992 . - pp. 31-44 : ill., graph., réf. Langues : Anglais (eng) Catégories : Thésaurus Agrovoc Photosynthèse ; Transpiration Résumé : To simulate radiation interception, the physical structure of plant canopies is defined by the inclination, orientation, and location of their foliage elements. Detailed models must consider all these factors, which has a significant impact on the required computation time. Simplifications of these models are possible, sacrificing accuracy for computation speed. An existing canopy radiation model was modified to incorporate an ellipsoidal distribution of foliage elements, which was continuous over the range of leaf angles and allowed for accommodation of horizontal or vertical tendencies of the canopy. The canopy was divided into thin layers, and the foliage elements within each layer were classified into nine leaf inclination and azimuth angle classes. Simplications of the model including options for varying the thickness of the canopy layers and the number of angle classes, for modeling the canopy as a single layer, and for partitioning the foliage elements in each layer into sunlit and shaded fractions, with disregard of leaf angle classes were also incorporated. This radiation model and its simplications were implemented in a computer simulation module for estimating canopy photosynthesis and transpiration. Simulation runs were performed for conditions with low and high leaf area index (lai) and irradiance. It was found that canopy photosynthesis and transpiration estimates, determined using canopy layer thickness of 0.5 lai and three inclination and azimuth angle classes, compared well (negligible error) with simulations using 0.1 lai and nine leaf angle classes, an standard recommendation for detailed models. If only photosynthesis estimates were of interest, even thicker layers could be used. Furthermore, errors were small if only average irradiance over sunlit and shaded leaf fractions by layer were considered, fluctuating from 0% to 4.3% for photosynthesis estimates, and from 0% to 2.7% for transpiration estimates. In many instances, a single layer divided into sunlit and shaded elements yielded reasonable results. Simplified canopy radiation models resulted in a dramatic decrease of computation time, up to View the MathML source of that required by the standard. Type de document : Tiré à part Permalien de la notice : https://infodoc.agroparistech.fr/index.php?lvl=notice_display&id=147554

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Ecological Modelling, Vol 67 - n°2-4. An object-oriented intracolonial and population level model of honey bees based on behaviors of european and africanized subspecies / M. E. Makela (1993)

Public ISBD Titre de série : Ecological Modelling, Vol 67 - n°2-4 Titre : An object-oriented intracolonial and population level model of honey bees based on behaviors of european and africanized subspecies Type de document : texte imprimé Auteurs : M. E. Makela, Auteur ; G. A. Rowell, Auteur ; W. J. Sames, Auteur ; L. T. Wilson, Auteur Année de publication : 1993 Importance : pp. 259-284 Présentation : graph., réf. Langues : Anglais (eng) Catégories : Thésaurus Agrovoc Dynamique des populations ; Colonie d'abeilles ; Essaimage ; Apis mellifera ; Apidae Résumé : A computer-based simulation model of a population of honey bee colonies, based on the biology of European and African races of Apis mellifera L., is described. The intracolonial dynamics of each colony are simulated each day based on parameters internal and external to the colony. The honey bee population is the collection of all colonies in the model at a particular point in time. Since most of the model development centers on structure and dynamics of the individual colony, the majority of the discussion will be at the intracoloniallevel. Nevertheless, there is no logical limit to the number of colonies that can be simulated simultaneously. Colonial birth and death processes cause the addition and deletion of colonies to the model as needed. A sample simulation is presented to illustrate both the intracolonialandpopulationlevel dynamics. Type de document : Tiré à part Permalien de la notice : https://infodoc.agroparistech.fr/index.php?lvl=notice_display&id=150035 Ecological Modelling, Vol 67 - n°2-4. An object-oriented intracolonial and population level model of honey bees based on behaviors of european and africanized subspecies [texte imprimé] / M. E. Makela, Auteur ; G. A. Rowell, Auteur ; W. J. Sames, Auteur ; L. T. Wilson, Auteur . - 1993 . - pp. 259-284 : graph., réf. Langues : Anglais (eng) Catégories : Thésaurus Agrovoc Dynamique des populations ; Colonie d'abeilles ; Essaimage ; Apis mellifera ; Apidae Résumé : A computer-based simulation model of a population of honey bee colonies, based on the biology of European and African races of Apis mellifera L., is described. The intracolonial dynamics of each colony are simulated each day based on parameters internal and external to the colony. The honey bee population is the collection of all colonies in the model at a particular point in time. Since most of the model development centers on structure and dynamics of the individual colony, the majority of the discussion will be at the intracoloniallevel. Nevertheless, there is no logical limit to the number of colonies that can be simulated simultaneously. Colonial birth and death processes cause the addition and deletion of colonies to the model as needed. A sample simulation is presented to illustrate both the intracolonialandpopulationlevel dynamics. Type de document : Tiré à part Permalien de la notice : https://infodoc.agroparistech.fr/index.php?lvl=notice_display&id=150035

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