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United States Department of Agriculture

Agricultural Research Service

Title: A Phenological Model of Global C3 and C4 Grass Distribution with Application to Climatic Change Scenarios with and Without Elevated Co2 Responses

Authors
item Winslow, J - UNIVERSITY OF WYOMING
item Hunt, Earle
item Piper, S - SCRIPPS INSTITUTION

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 19, 2002
Publication Date: May 1, 2003
Citation: Winslow, J.C., Hunt, E.R., Piper, S.C. 2003. A phenological model of global C3 and C4 grass distribution with application to climatic change scenarios with and without elevated CO2 responses. Ecological Modeling. 163(5):153-173.

Interpretive Summary: Global distributions of grasses with the C3 and C4 photosynthetic pathways are related to climate. These distributions are expected to change under climatic change and elevated CO2. To better understand and characterize the distributions of C3 and C4 grasses, we developed a model. First, we divided grasslands into three categories: (I) all C, (II) mixed C3/C4, and (III) all C4, based upon the timing of the growing season. Second, for the mixed regions only, we predicted the fractional of C3 biomass based on available water and water use efficiency. We applied the model globally using 14 years of daily weather data and compared predictions with data at 142 points in North America, Argentina, Australia, and Africa. To examine how C3/C4 distribution might change, we applied it to historical climate data for the United States and a scenario for doubled atmospheric CO2. Without any ameliorating effects of elevated CO2 on C3 photosynthesis, C3 grasses drastically decreased in abundance. With ameliorating effects of elevated CO2, the decrease of C3 biomass was significant compared to historical climate, but not as much as without the ameliorating effects. The model presented here is important because global climatic change may affect conservation efforts for native vegetation communities and may affect agricultural production because most small grains have C3 photosynthesis.

Technical Abstract: Global distributions of C3 and C4 grasses are related to climate. These distributions are expected to change under climatic change and elevated CO2. To better understand and characterize the distributions of C3 and C4 grasses, we developed a model. First, we divided grasslands into three categories: (I) all C, (II) mixed C3/C4, and (III) all C4, based upon the timing of the active growth periods. Second, for the mixed regions only, we predicted the fractional biomass of C3 grasses based available water and water use efficiencies. We applied the model globally using 14 years (1983 to 1994) of daily weather data and compared predictions with data at 142 points in North America, Argentina, Australia, and Africa. The model correctly classified the category at 76% of the points, and in the mixed C3/C4 region, the model predicted fraction of C3 biomass with an R2 = 0.54. To examine how C3/C4 distribution might change, we applied it to the VEMAP historical climate data for the United States and a VEMAP scenario for doubled atmospheric CO2 from the Canadian Climate Centre Global Climate Model. Without any ameliorating effects of elevated CO2 on C3 photosynthesis, grasses with C3 photosynthesis drastically decreased in abundance. With ameliorating effects of elevated CO2, the decrease of C3 biomass was significant compared to historical climate, but not as much as without the ameliorating effects. The model presented here is a positive step toward explaining the distribution of C3/C4 grasslands on a more mechanistic basis.

Last Modified: 10/1/2014
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