Reforestation of agricultural land in the tropics: The relative contribution of soil, living biomass and debris pools to carbon sequestration

Tom Lewis; Luke Verstraten; Bruce Hogg; Bernhard J Wehr; Scott Swift; Neil Tindale; Neal W Menzies; Ram C Dalal; Philippa Bryant; Ben Francis; Timothy E Smith

doi:10.1016/j.scitotenv.2018.08.351

Reforestation of agricultural land in the tropics: The relative contribution of soil, living biomass and debris pools to carbon sequestration

Sci Total Environ. 2019 Feb 1:649:1502-1513. doi: 10.1016/j.scitotenv.2018.08.351. Epub 2018 Aug 29.

Authors

Affiliations

¹ Department of Agriculture and Fisheries, Queensland Government, University of the Sunshine Coast, Sippy Downs 4556, Australia; Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Sippy Downs 4556, Australia. Electronic address: tom.lewis@daf.qld.gov.au.
² Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Sippy Downs 4556, Australia.
³ Department of Agriculture and Fisheries, Queensland Government, University of the Sunshine Coast, Sippy Downs 4556, Australia.
⁴ School of Agriculture and Food Sciences, The University of Queensland, St Lucia 4072, Australia.
⁵ Department of Agriculture and Fisheries, Queensland Government, University of the Sunshine Coast, Sippy Downs 4556, Australia; Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Sippy Downs 4556, Australia.

PMID: 30308918
DOI: 10.1016/j.scitotenv.2018.08.351

Abstract

Tropical regions of the world experience high rates of land-use change and this has a major influence on terrestrial carbon (C) pools and the global C cycle. We assessed land-use change from agriculture to reforested plantings (with endemic species), up to 33 years of age, using 10 paired sites in the wet tropics, Australia. We determined the impacts on 0-50 cm below-ground C (soil organic C (SOC), charcoal C, humic organic C, particulate organic C, resistant organic C), C stored in roots (fine and coarse), C stored in living above-ground biomass and debris C pools. Reforested areas accumulated ecosystem C at a rate of 7.4 Mg ha^-1 yr^-1. Reforestation plantings contained, on average, 2.3 times more ecosystem C than agricultural areas (102 Mg ha^-1 and 233 Mg ha^-1, respectively). Most of the C accumulation was in living above-ground and below-ground biomass (60 and 30%, respectively) with a smaller amount in debris pools (16%). Apart from C in roots, soil C accumulation was not obvious across sites ranging from 8 to 33 years since reforestation, relative to the agricultural baseline. Differences in SOC (and associated SOC pools) to a depth of 50 cm, did exist between reforested areas and adjacent agriculture at some sites, however there was not a consistent trend in SOC associated with reforestation. Local site-based factors (e.g. soil texture and mineralogy, land-use history and microbial activity) appear to have a strong influence on the direction of the change in SOC. While reforestation in the tropics has great potential to accumulate C in biomass in living vegetation, and debris pools, it is likely to take approximately 50 years before C stocks of reforested areas resemble natural ecosystems. Accumulation of SOC through reforestation is difficult to achieve, highlighting the need to conserve carbon pools in remnant forests in the tropics.

Keywords: Ecosystem carbon stocks; Litter; Organic matter; Rainforest; Restoration planting; Soil organic carbon; Tree biomass.