PARENT SESSION
Oral Session #27: Fire Ecology.
Presiding: C. Allen
Tuesday, August 6. 8:00 AM to 11:30 AM. Graham Meeting Room, TCC.

Effects of wildfire-induced changes in plant community composition on ecosystem CO₂ and water vapor fluxes in the Great Basin.

Obrist, Daniel^*,1,2, Arnone III, John^1,2, ¹ Desert Research Institute, Reno, NV² University of Nevada, Reno, NV

ABSTRACT- The objectives of this study were (1) to quantify how wildfire-induced shifts in plant community structure, from native Great Basin sagebrush ecosystems to post-fire successional plant communities, affect whole ecosystem CO₂ (NEE) and H₂O vapor exchange (ET) and (2) to calculate yearly budgets for NEE and ET. Results of gas exchange measurements in adjacent sagebrush and post-fire ecosystems using a large (16 m³) static chamber showed significantly lower daily NEE (P= 0.02) and ET (P<0.001) in sagebrush communities 2 years after the fire early in the growing season when LAIs were similar in both systems. Differences in NEP and ET between the two plant communities disappeared when increasingly dry conditions drove NEP and ET downward. Cumulative annual NEP was 22.8±6.0 g C m^-2 yr^-1 in post-fire communities (i.e. C gain) compared to -16.0±8.0 g C m^-2 yr^-1 in intact sagebrush ecosystems (i.e. C loss), while cumulative ET was 87.4±5.5 mm H₂O yr^-1 and 67.6±4.0 mm H₂O yr^-1, respectively. Our results indicate that in an atypically dry year (1) ecosystem C losses via respiration can exceed C uptake in intact sagebrush ecosystems, whereas further C losses from post-fire ecosystems are stemmed by positive annual NEP; and (2) higher soil water recharge and higher soil temperatures in post-fire ecosystems caused ET to exceed that observed in deeper-rooted sagebrush ecosystems.

KEY WORDS: Ecosystem carbon and water fluxes, post-fire plant succession, sagebrush (Artemisia tridentata), cheatgrass (Bromus tectorum)