Submitted to: Ecological Modelling
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/7/2001
Publication Date: 6/1/2002
Citation: PETERS, D.C. PLANT SPECIES DOMINANCE AT A GRASSLAND-SHRUBLAND ECOTONE: AN INDIVIDUAL-BASED GAP DYNAMICS MODEL OF HERBACEOUS AND WOODY SPECIES. ECOLOGICAL MODELLING. 2002. V. 152(1). P. 5-32. Interpretive Summary: An individual-plant based simulation model was developed to examine the relationship between plant life history traits, climate and soil processes at a semiarid-arid biome transition zone. The model (ECOTONE) simulates the recruitment, growth and mortality of individual plants through time at an annual time step. The model contains a sub-module that simulates soil water rdaily and a sub-module that simulates nitrogen monthly. ECOTONE was parameterized for two soil types at the Sevilleta National Wildlife Refuge. Shortgrass steppe communities are dominated by perennial grass blue grama and Chihuahuan desert communities by perennial grass black grama or shrub creosotebush. Experiments were conducted to provide key parameters related to recruitment and growth that were supplemented with information from the literature for remaining parameters. Simulation analyses were conducted under current climate and for a directional change in climate. Under current climatic conditions, simulated biomass on sandy loam soils was dominated by black grama with smaller biomass of blue grama. Simulated biomass on a loamy sand soil was codominated by black grama and creosotebush. Under a GFDL climate change scenario of increased year-round temperatures and increased summer precipitation, vegetation patterns shifted to a clear dominance of biomass by black grama on both soil types. These results show that temporal partitioning of soil water is important to codominance by the two grasses, and that spatial and temporal partitioning of soil water is important for grass-shrub interactions. Results also suggest global climate change may provide a mechanism for recovery of black grama following shrub invasion in the Southwestern US.
Technical Abstract: This study examined the relationship between plant life history traits and patterns in dominance and composition at a grassland-shrubland transition zone to predict shifts in dominance with directional changes in climate. A mixed lifeform individual plant-based gap dynamics model (ECOTONE) was developed to examine consequences of differences in recruitment, resource acquisition and mortality to patterns in species dominance and composition under a variety of soils and climatic conditions. ECOTONE was parameterized for 2 soil types at the Sevilleta National Wildlife Refuge. Shortgrass steppe communities are dominated by the perennial grass Bouteloua gracilis and Chihuahuan desert communities are dominated by the perennial grass Bouteloua eriopoda or the shrub Larrea tridentata. Under current climatic conditions, simulated biomass on sandy loam soils was dominated by B. eriopoda with smaller biomass of B. gracilis and other species groups. By contrast, simulated biomass on loamy sand soil was codominated by B. eriopoda and L. tridentata with small biomass attributed to other species groups. Under a GFDL climate change scenario of increased year-round temperatures and increased summer precipitation, vegetation patterns shifted to a clear dominance of biomass by B. eriopoda on both soil types. Results show temporal partitioning of soil water is important to codominance by the 2 Bouteloua species and spatial and temporal partitioning of soil water is important for grass-shrub interactions. This modeling approach is useful in improving understanding key processes driving these vegetation dynamics as well as predicting shifts in dominance as environmental conditions change.