Carbon and greenhouse gas balances in an age-sequence of temperate pine plantations

Abstract

Abstract. This study investigated differences in the magnitude and partitioning of the carbon (C) and greenhouse gas (GHG) balances in an age-sequence of four white pine (Pinus strobus L.) afforestation stands (7, 20, 35 and 70 years old as of 2009) in southern Ontario, Canada. The 4 year (2004–2008) mean annual carbon dioxide (CO2) exchanges, based on biometric and eddy covariance data, were combined with the 2-year means of static chamber measurements of methane (CH4) and nitrous oxide (N2O) fluxes (2006–2007) and dissolved organic carbon (DOC) export below 1 m soil depth (2004–2005). The total ecosystem C pool increased with age from 9 to 160 t C ha−1 across the four stands. Rates of organic matter cycling (i.e. litter-fall and decomposition) were similar among the three older stands. In contrast, considerable differences related to stand age and site quality were observed in the magnitude and partitioning of individual CO2 fluxes showing a peak in production and respiration rates in the middle-age (20 year-old) stand growing on fertile post-agricultural soil. The DOC export accounted for 10% of net ecosystem production (NEP) at the 7 year old stand but < 2% at the three older stands. The GHG balance from the combined exchanges of CO2, CH4 and N2O fluxes was 2.6, 21.6, 13.5 and 4.8 t CO2 eq ha−1 yr−1 for the 7, 20, 35, and 70 year-old stands, respectively. The maximum annual contribution from the combined exchanges of CH4, N2O and DOC to the GHG balance was 8% and 15% in the 7 and 70 year-old stands, respectively, but < 1% in the two highly productive middle-age (20 and 35 year-old) stands. Averaged over the entire age-sequence, the CO2 exchange was the main driver of the GHG balance in these forests. The cumulative CO2 sequestration over the 70 years was estimated at 129 \\unit{t} C and 297 t C ha−1 yr−1 for stands growing on low and high productive sites, respectively. This study highlights the importance of accounting for age and site quality effects on forest C and GHG balances. It further demonstrates a large potential for C sequestration and climate benefits (i.e. cooling effect) gained through afforestation of marginal agricultural and fallow lands in temperate regions.

The Net Landscape Carbon Balance—Integrating terrestrial and aquatic carbon fluxes in a managed boreal forest landscape in Sweden

“…The amount of aquatic C exports in the forms of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC; i.e., , , and ), and dissolved CO 2 and CH 4 reflect furthermore the aquatic‐terrestrial links between water bodies and the surrounding soil and plants within the landscape (Cole et al, ). DOC fluxes vary with different stand ages (Justine et al, ; Peichl, Arain, et al, ; Peichl et al, ) and may account for up to 20% of annual net CO 2 uptake in boreal forest stands (Öquist et al, ). DIC fluxes together with the supersaturated CO 2 and CH 4 in the stream discharge (i.e., dissolved CO 2 and CH 4 fluxes) represent a significant channel of C transformation and cycling at the landscape scale (Wallin et al, ).…”

“…Meanwhile, thinning may have a minor effect on the annual net CO 2 uptake (Lindroth et al, ) but may reduce soil CH 4 uptake in boreal forests (Vesala et al, ; Vestin, ). Harvest operations can also result in large amounts of C export and a mosaic of tree stands with various ages, which may act as either sinks or sources of GHGs (Litvak et al, ; Peichl, Arain, et al, ; Peichl, Arain, & Brodeur, ). Furthermore, management activities to enhance tree growth such as nitrogen fertilization and drainage ditching may locally enhance biomass production and alter the ecosystem C storage and dynamics (e.g., Lim et al, ; Lohila et al, ).…”