Contrasting responses to drought of forest floor CO 2 efflux in a Loblolly pine plantation and a nearby Oak‐Hickory forest

• Published in: Global change biology Vol. 11; no. 3; pp. 421 - 434
• Main Authors: Palmroth, S., Maier, C. A., McCarthy, H. R., Oishi, A. C., Kim, H.‐S., Johnsen, K.H., Katul, G. G., Oren, R.
• Format: Journal Article
• Language: English
• Published: 01.03.2005
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/j.1365-2486.2005.00915.x

Abstract Forest floor CO 2 efflux ( F ff ) depends on vegetation type, climate, and soil physical properties. We assessed the effects of biological factors on F ff by comparing a maturing pine plantation (PP) and a nearby mature Oak‐Hickory‐type hardwood forest (HW). F ff was measured continuously with soil chambers connected to an IRGA during 2001–2002. At both sites, F ff depended on soil temperature at 5 cm ( T 5 ) when soil was moist (soil moisture, θ >0.20 m 3  m −3 ), and on both T 5 and θ when soil was drier. A model ( F ff ( T 5 , θ )) explained 92% of the variation in the daily mean F ff at both sites. Higher radiation reaching the ground during the leafless period, and a thinner litter layer because of faster decomposition, probably caused higher soil temperature at HW compared with PP. The annual F ff was estimated at 1330 and 1464 g C m −2  yr −1 for a year with mild drought (2001) at PP and HW, respectively, and 1231 and 1557 g C m −2  yr −1 for a year with severe drought (2002). In the wetter year, higher soil temperature and moisture at HW compared with PP compensated for the negative effect on F ff of the response to these variables resulting in similar annual F ff at both stands. In the drier year, however, the response to soil temperature and moisture was more similar at the two stands causing the difference in the state variables to impel a higher F ff at HW. A simple mass balance indicated that in the wetter year, C in the litter–soil system was at steady state at HW, and was accruing at PP. However, HW was probably losing C from the mineral soil during the severe drought year of 2002, while PP was accumulating C at a lower rate because of a loss of C from the litter layer. Such contrasting behavior of two forest types in close proximity might frustrate attempts to estimate regional carbon (C) fluxes and net C exchange.