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Changes in Soil Carbon Following Afforestation

DOI: 10.3334/CDIAC/tcm.008

Forest Ecology and Management 168:241-257 (2002)

K. I. Paul, P. J. Polglase, J. G. Nyakuengama, P. K. Khanna
CSIRO Forestry and Forest Products
P.O. Box E4008
Kingston, ACT 2604, Australia

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Australia's Commonwealth Scientific and Industrial Research Organisation

Sponsor: Australian Greenhouse Office

Abstract

Quantifying changes in soil C may be an important consideration under large-scale afforestation or reforestation. We reviewed global data on changes in soil C following afforestation, available from 43 published or unpublished studies, encompassing 204 sites. Data were highly variable, with soil C either increasing or decreasing, particularly in young (<10-y) forest stands. Because studies varied in the number of years since forest establishment and the initial soil C content, we calculated change in soil C as a weighted average (i.e. sum of C change divided by sum of years since forest establishment) relative to the soil C content under previous agricultural systems at <10 cm, >10 cm and <30 cm sampling depths. On average, soil C in the <10 cm (or <30 cm) layers generally decreased by 3.46% y–1 (or 0.63% y–1) relative to the initial soil C content during the first five years of afforestation, followed by a decrease in the rate of decline and eventually recovery to C contents found in agricultural soils at about age 30. In plantations older than 30 years, C content was similar to that under the previous agricultural systems within the surface 10 cm of soil, yet at other sampling depths, soil C had increased by between 0.50 and 0.86% y–1. Amounts of C lost or gained by soil are generally small compared with accumulation of C in tree biomass.

The most important factors affecting change in soil C were previous land use, climate and the type of forest established. Results suggest that most soil C was lost when softwoods, particularly Pinus radiata plantations, were established on ex-improved pastoral land in temperate regions. Accumulation of soil C was greatest when deciduous hardwoods, or N2-fixing species (either as an understorey or as a plantation), were established on ex-cropped land in tropical or subtropical regions. Long-term management regimes (e.g., stocking, weed control, thinning, fertilizer application and fire management) may also influence accumulation of soil C. Accumulation is maximised by maintaining longer (20-50 year) forest rotations. Furthermore, inclusion of litter in calculations reversed the observed average decrease in soil C, so that amount of C in soil and litter layer was greater than under preceding pasture.

Reprint available from Elsevier Science.

This table provides a quick look at some of the data available from this publication. For the complete data set, please contact Keryn Paul.

Location Layer (cm) Age (y) Climate1 Ex-land use2 Forest spp. Initial soil C (g C/m2) Final soil C
(g C/m2)
Change
(g C/m2)
Change
(% initial)
Augusta, WA 0-10 cm 4 3 1 E. globulus 4974 5422 448 9.01
0-20 cm 7772 8540 768 9.88
10-20 cm 2798 3118 320 11.44
Nigeria 0-10 cm 3 1 2 Succession 1482 1188 -293 -19.81
0-30 cm 3374 2954 -420 -12.44
10-30 cm 1892 1766 -126 -6.68
continued...

1Climate: 1 = Subtropical wet/Savanna; 3 = Mediterranean/Marine temperate.
2Ex-land use: 1 = Ex-pasture; 2 = Ex-crops.

For related work, see:

  • Polgase et al. (2000) Change in Soil Carbon Following Afforestation or Reforestation. National Carbon Accounting System Technical Report No. 20, Australian Greenhouse Office.
  • Paule et al. (2003) Predicted change in soil carbon following afforestation or reforestation, and analysis of controlling factors by linking a C accounting model (CAMFor) to models of forest growth (3PG), litter decompoistion (GENDEC) and soil C turnover (RothC) Forest Ecology and Management 177: 485-501.
  • Paul et al. (2003) Sensitivity analysis of predicted change in soil carbon following afforestation Ecological Modelling 164:137-152.

lak 04/2003