Presenter/Author Information

J. Raventós
M. F. Acevedo
J. Segarra

Keywords

grass plants, savanna, individual-based model, matrix model

Start Date

1-7-2002 12:00 AM

Description

We developed a model of grass plant growth as a collection of the individual dynamic behavior of shoots inspired in data for plants of three species (Elyonurus adustus, Leptocoryphium lanatum and Andropogon semiberbis) of common grasses in the Venezuelan savannas. These species represent various types of architecture and regeneration response to fire. The individual-shoot model is based on shoot emergence, mortality, and elongation given by Richards’ equation, plus a few simple geometric considerations. Model output is shoot density in each cell of a square grid at several vertical levels. Differences in patterns of shoot density among species are explained by changing a set of parameter values related to growth form and phenology. Vertical distribution of shoot density was calculated from the simulation results and the field data with the purpose of deriving a simpler lumped shoot-population model. This simpler demographic model is based on a projection matrix that predicts the essential dynamics of growth in the vertical dimension. The final and transient behavior of vertical distribution of shoot density are calculated with the matrix model and compared to field data yielding good fit. The matrix model can be used for scaling-up the individual-shoot model to larger areas, or applied to generate plant functional types for analysis of savanna dynamics subject to fire.

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Jul 1st, 12:00 AM

Growth dynamics of tropical savanna grasses: from individual shoots to plant models

We developed a model of grass plant growth as a collection of the individual dynamic behavior of shoots inspired in data for plants of three species (Elyonurus adustus, Leptocoryphium lanatum and Andropogon semiberbis) of common grasses in the Venezuelan savannas. These species represent various types of architecture and regeneration response to fire. The individual-shoot model is based on shoot emergence, mortality, and elongation given by Richards’ equation, plus a few simple geometric considerations. Model output is shoot density in each cell of a square grid at several vertical levels. Differences in patterns of shoot density among species are explained by changing a set of parameter values related to growth form and phenology. Vertical distribution of shoot density was calculated from the simulation results and the field data with the purpose of deriving a simpler lumped shoot-population model. This simpler demographic model is based on a projection matrix that predicts the essential dynamics of growth in the vertical dimension. The final and transient behavior of vertical distribution of shoot density are calculated with the matrix model and compared to field data yielding good fit. The matrix model can be used for scaling-up the individual-shoot model to larger areas, or applied to generate plant functional types for analysis of savanna dynamics subject to fire.