Modeling Questions and Models

In the following, we present an overview over the most important grassland models, structured by their scientific questions rather than by model type. A summary of these models is given in Table 1. The major variables and properties of ecological grassland models are temporal and spatial grassland dynamics and diversity, grassland

Table 1 Overview of different exemplary modeling studies in grasslands

Authors

Type of model

Description

Area

Rangeland models Westoby etal. (1989)

Noy-Meir (1975)

Fernandez-Gimenez and Allen-Diaz (1999)

Bosch and Gauch

(1991) Phelps and Bosch (2002)

Conceptual

Nonspatial differential equation Conceptual

Statistical Statistical

Alternative stable states with discontinuous and irreversible transitions, nonequilibrium dynamics Applies classical predator-prey models to plant-

herbivore systems, detects dual stability Assesses the extent to which the current nonequilibrium models of rangeland vegetation dynamics apply Description of degradation gradient method for range condition assessment Degradation gradient method in conjunction with state-and-transition models of rangeland dynamics and condition

Spatially explicit models on succession and disturbance in grasslands

Coffin and Lauenroth (1989, 1990)

Coffin and Urban (1993)

Lauenroth etal. (1993)

Peters (2002)

Moloney and Levin (1996)

Wu and Levin (1994)

Tan and Smeins (1996)

O'Connor (1993)

Gap model, simulations

Gap models, simulations

STEPPE, CENTURY, simulations

Gap model, similar to STEPPE, simulations

Spatially explicit, grid-based, simulations

Spatially explicit patch-based model

Statistical model, neural networks

Size-structured matrix models

Introduction to STEPPE model, evaluates the effects of disturbances at the scale of a landscape for a semiarid grassland Compares the STEPPE model to a structurally similar gap model for forest dynamics (ZELIG) Couples two models to study interactions between vegetation structure and ecosystem processes

Studies effects of climatic fluctuations and disturbance on regional patterns of vegetation dynamics at an arid-semiarid grassland ecotone Varies components of disturbance architecture systematically to determine their impact on population dynamics at the scale of the landscape Studies landscape pattern and process dynamics

Predicts grassland community changes with an artificial neural network model

Investigates how population growth rate depends on factors such as rainfall or grazing

Optimal life-history strategies, competition, coexistence, and biodiversity

Lavorel et al. (1994)

Spatially explicit, two-species, simulation

Matsinos and Troumbis Cellular automaton (2002) model

Schwinning and Parsons (1996)

Thornleyetal. (1995)

Winkler and Fischer (2002)

Bolker and Pacala (1999)

Spatially explicit cellular automaton model

Physiological models Grid-based model

Analytical model, moment equations

Spatial structures in arid and semiarid grasslands Dunkerley (1997) Cellular automaton model

Spatiotemporal dispersal strategies and annual plant species coexistence in a structured landscape

Models competition, dispersal and effects of disturbance in the dynamics of a grassland community

Extends a pasture model by Thornley etal. in 1995 to study coexistence mechanisms for grasses and legumes including selective grazing and spatial considerations

Studies complex dynamics in a carbon-nitrogen model of a grass-legume pasture

Investigates the role of vegetative and seed dispersal within habitats for optimal life histories of clonal plants

Aims to understand at a general level how plants coexist in communities

Investigates the development of banded vegetation communities in grass- and shrublands

Arid and semiarid rangelands

Mongolian rangeland ecosystems

Grasslands of South Africa

Mitchell grasslands, central western Queensland, Australia

Semiarid grassland in north-central Colorado, USA

Semiarid grassland in north-central Colorado, USA Chihuahuan desert, central New Mexico, USA Jasper Ridge serpentine grassland, USA Jasper Ridge serpentine grassland, USA Grassland communities near Hays, Kansas, USA Perennial grasses of two African savannas

Species-rich Mediterranean old-fields Grasslands in Lesbos, Greece

Perennial rye-grass and white clover communities

Western NSW grassand shrublands, Australia

(Continued )

Table 1 (Continued)

Authors

Type of model

Description

Area

Rietkerk et al. (2004) Partial differential equations, numerical simulations

Modeling primary production in grasslands Le Houerou et al. (1988) Regression models

Paruelo et al. (1999) Regression models and NDVI

Paruelo et al. (1997, 2000)

Prince (1991)

Ecosystem modeling and Nouvellon etal. (2001)

Van Dyne (1972)

Coughenour and Chen (1997)

Parton etal. (1993)

Gilmanovetal. (1997) Hibbard etal. (2003)

Regression models, NDVI

Satellite remote sensing flows of energy and matter Remote sensing, ecosystem model

Linked ecosystem model

CENTURY

CENTURY

CENTURY and matrix transition model

Paruelo and Sala (1995) Water balance model

Investigates vegetation pattern formation in arid ecosystems and hypothesizes that they may be the result of spatial self-organization, caused by net displacement of surface water to vegetated patches

Relationship between the variability of primary production and the variability of annual precipitation in world arid lands Studies how grassland precipitation-use efficiency varies across a resource gradient. Uses 11 temperate grassland sites worldwide, and 19 grassland sites across the central grassland region of North America Estimates ANPP for the central grassland region of the US and subhumid pampa rangelands in Argentina

Determines primary production for Sahelian grasslands, 1981-88

in grasslands

Couples a grassland ecosystem model for semiarid perennial grasslands with Landsat imagery to calibrate parameters of ecosystem model Describes organization and management of an IBP

'big biology' program. Assessment of grassland ecosystem responses to atmospheric change using linked plant-soil process models

Parametrizes CENTURY for the world's major grassland types to model biomass and soil organic-matter dynamics in grasslands Uses long-term data from several sites to assess the performance of CENTURY Linked CENTURY to a transition matrix model to simulate the displacement of grassland communities under heavy livestock grazing and climate events Calculates the amount of water evaporated from the soil and transpirated by the canopy to estimate water losses in a Patagonian steppe

Arid lands of the world

Grassland sites worldwide

Central grassland (USA), subhumid pampa (Argentina) Sahelian grasslands

Grasslands in southeastern Arizona (USA)

Grasslands of Colorado and Kansas (USA) and Kenya Grassland biome worldwide

Grassland and thorn woodland in southern Texas (USA)

Shrub-grass steppe in Patagonia (Argentina)

productivity, water dynamics, and flow of other matter and nutrients. Grazing is a predominant theme in grassland models. It has been discussed in Grazing Models.

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