Document: JIM-3-68-26

CO₂ flux in burned and unburned Prosopis savanna: Comparing Bowen ratio and leaf chamber photosynthesis.

ANSLEY, R.J.* ¹, W.A.DUGAS ² and B.A.KRAMP ¹

Texas A&M Univ. Agricultural Experiment Station, Vernon, TX, USA ¹
Texas A&M Univ. Blackland Research Center, Temple, TX, USA ²

Abstract:
The objective of the study was to quantify CO₂ flux in a honey mesquite (Prosopis glandulosa) savanna in north Texas, USA the growing season following a winter fire when compared to an unburned Prosopis control site. Flux measurements occurred in mid-summer during a wet and a drought year with a different area burned each year. Fires killed most stems and stimulated coppice growth in Prosopis. Two methods were used to quantify CO₂ flux: Bowen Ratio/Energy Balance (BREB), which provided an integrated landscape measurement net uptake, and leaf chamber photosynthesis of key species (Prosopis, Nasella leucotricha, Buchloe dactyloides) scaled to a landscape level using small plot biomass, live leaf area and species composition estimates. BREB measurements indicated CO₂ uptake was 29.3 and 9.9 g m^-2 d^-1 on the unburned site, and 28.5 and 3.3 g m^-2 d^-1 on burned sites in the wet and drought year, respectively. Scaled CO₂ flux estimates were within 20 percent of BREB values. Leaf photosynthesis of coppice Prosopis on burned sites was 2 to 3 times greater than that of undamaged trees in the control, possibly due to greater root:stem ratio created by burning. However, total Prosopis leaf area was much less on burned sites. Results suggest that drought following fire may reduce carbon assimilation when compared to unburned areas.

Keywords: Mesquite,Prosopis, fire, carbon dioxide, photosynthesis

This abstract is being presented at: 10:30 AM in session:
Poster Session #12: Disturbance Ecology.