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

M. R. Pejam,A. M. Arain,J. McLaren,S. Ullah,M. Peichl,M. Khomik,T. R. Moore,N. Restrepo-Coupé,J. J. Brodeur

doi:10.5194/bg-11-5399-2014

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 46 to 197 t C ha−1 across the four stands. Rates of organic matter cycling (i.e. litterfall 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 was 2.6, 21.6, 13.5 and 4.8 t CO2 equivalent ha−1 year−1 for the 7-, 20-, 35- and 70-year-old stands, respectively. The maximum annual contribution from the combined exchanges of CH4 and N2O to the GHG balance was 13 and 8% 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 t C and 297 t C ha−1 year−1 for stands growing on low- and high-productivity 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 net C sequestration and climate benefits gained through afforestation of marginal agricultural and fallow lands in temperate regions.

Highlights

The global temperature increase over the past century has been attributed to increasing concentrations of atmospheric greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), among others, coupled with human activities and natural processes in terrestrial ecosystems (Houghton et al, 1998; IPCC, 2013; Schimel, 1995; Schulze et al, 2009)
Peichl et al.: Carbon and greenhouse gas balances in a forest age sequence (a) and decomposition is a major determinant of the accumulation and partitioning of organic matter into soil organic carbon accumulation and losses due to heterotrophic respiration (Yang et al, 2011)
We combined C pools and fluxes of CO2, CH4, N2O and dissolved organic carbon (DOC) to estimate C and GHG balances for an age sequence of afforested white pine stands in the temperate region of southern Ontario, Canada

Summary

Introduction

The global temperature increase over the past century has been attributed to increasing concentrations of atmospheric greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), among others, coupled with human activities (e.g. fossil fuel burning, deforestation) and natural processes in terrestrial ecosystems (Houghton et al, 1998; IPCC, 2013; Schimel, 1995; Schulze et al, 2009). Forest ecosystems have the strongest carbon (C) sink potential and provide stocks of 100 to 160 Gt C in biomass and soil in temperate regions alone (Dixon et al, 1994; Goodale et al, 2002; Pan et al, 2011; Reich, 2011). Much of the current CO2 sink strength of the Northern Hemisphere has been attributed to re-growth and afforestation of former agricultural land in the US and Canada (Pan et al, 2011; Reich, 2011). Further afforestation of former agricultural lands of low productivity has been proposed to help offset the increasing concentration of atmospheric CO2 (Bárcena et al, 2014; Brown, 2002; Goodale et al, 2002; Nabuurs et al, 2007; Niu and Duiker, 2006)

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