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United States Department of Agriculture

Agricultural Research Service

Research Project: HYDROLOGIC PROCESSES, SCALE, CLIMATE VARIABILITY, AND WATER RESOURCES FOR SEMIARID WATERSHED MANAGEMENT

Location: Southwest Watershed Research

Title: Temporally-limited herbaceous plants significantly contribute to semi-arid woodland ecohydrological fluxes

Authors
item Tyler, A.P. -
item SCOTT, RUSSELL
item Huxman, T.E. -

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: September 30, 2010
Publication Date: December 13, 2010
Citation: Tyler, A., Scott, R.L., Huxman, T. 2010. Temporally-limited herbaceous plants significantly contribute to semi-arid woodland ecohydrological fluxes. American Geophysical Union 2010 Fall Meeting, [Abstract]. AGU, San Francisco, Calif., 13-17 Dec.

Interpretive Summary: Study of the ephemeral components of ecosystems is often overlooked, yet can be important to our understanding of their ecology, how they affect and interact with biotic and abiotic controls of carbon and water cycling, and to improve our estimates of the components of ecohydrological fluxes given shifts in vegetation structure and climate. Grasslands in the semi-arid areas of the southwestern US have been experiencing increasing woody plant encroachment to become shrublands and woodlands due to factors such as historic changes grazing intensity, fire frequency, and changing atmospheric conditions. In a semi-arid riparian woodland in SE Arizona, ephemeral annual and biennial plants are present and active only during the summer monsoon period, yet they constitute a significant proportion of the ecosystem’s photosynthetic biomass. We have found that although their standing biomass is small compared to the dominant perennial shrubs and trees, these ephemeral herbs represent seasonal bursts of increased activity and primary production disproportional to their standing stock. We are finding that when scaled up to the ecosystem level, these ephemeral plants can contribute up to 30% of ecosystem carbon fixation, and affect 20% of morning evapotranspiration. This level of episodic carbon fixation and water flux should be included in our characterization of these systems coupled carbon and water dynamics.

Technical Abstract: Study of the ephemeral components of ecosystems is often overlooked, yet can be important to our understanding of their ecology, how they affect and interact with biotic and abiotic controls of carbon and water cycling, and to improve our estimates of the components of ecohydrological fluxes given shifts in vegetation structure and climate. Grasslands in the semi-arid areas of the southwestern US have been experiencing increasing woody plant encroachment to become shrublands and woodlands due to factors such as historic changes grazing intensity, fire frequency, and changing atmospheric conditions. In a semi-arid riparian woodland in SE Arizona, ephemeral annual and biennial plants are present and active only during the summer monsoon period, yet they constitute a significant proportion of the ecosystem’s photosynthetic biomass. We have found that although their standing biomass is small compared to the dominant perennial shrubs and trees, these ephemeral herbs represent seasonal bursts of increased activity and primary production disproportional to their standing stock. We are finding that when scaled up to the ecosystem level, these ephemeral plants can contribute up to 30% of ecosystem carbon fixation, and affect 20% of morning evapotranspiration. This level of episodic carbon fixation and water flux should be included in our characterization of these systems coupled carbon and water dynamics.

Last Modified: 8/19/2014
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