PARENT SESSION
Oral Session #93: Forest Carbon Dynamics: Soils and litter.
Presiding: J. Ward
Thursday, August 8. 1:00 PM to 3:45 PM. Grand Ballroom Central, Radisson.

Forest floor CO₂ efflux - a comparison of instantaneous and seasonal flux between a pine and an oak-hickory forest.

PALMROTH, SARI^*,1, BUTNOR, JOHN², MCCARTHY, HEATHER¹, MAIER, CHRISTOPHER², STOY, PAUL¹, KATUL, GABRIEL¹, OREN, RAM¹, ¹ Duke University, Durham, NC² US Forest Service, Research Triangle Park, NC

ABSTRACT- Net ecosystem carbon exchange is the balance between gross primary production and ecosystem respiration (R_E). CO₂ efflux from the forest floor (F_ff) reflects the production rate of CO₂ and its transport to the surface. Thus, F_ff depends on the vegetation cover, climate, and the physical properties of the site. We aimed at extracting the contribution to CO₂ efflux of biological differences between forest types by comparing two stands, a pine plantation (PP) and an Oak-Hickory type forest (HF), under identical climatic and edaphic conditions. We analyzed instantaneous to seasonal integrals of F_ff and R_E measured continuously at the two forests in 2001. The shape and dynamics of the instantaneous responses of F_ff to temperature were different in the two forest types, probably reflecting the availability of recently assimilated carbohydrates at PP and a combination of greater standing biomass and more easily decomposable litter at HF. The seasonal dynamics of CO₂ efflux was more apparent at HF, where the leaf area index changed between <1 and 4, than at PP, where it changed between 3 and 5. The ratio of nighttime F_ff to R_E was similar in both ecosystems, showing a general tendency to increase from 0.4 to 0.6 during the early part of the growing season, increasing thereafter more at PP than at HF. Yearly estimates of F_ff were 1270 and 1370 g C m^-2 at HF and PP, respectively.

KEY WORDS: ecosystem respiration, chamber measurements, eddy covariance