Abstract
Tropical deforestation reduces the global terrestrial carbon sink and substantially contributes towards global climate change. Conversely, tropical forest restoration could help to mitigate the problem, but few measurements of how much carbon can be absorbed by forest restoration have been published. Therefore, this study used a partial harvesting method to compare carbon sequestration among 11 framework tree species (selected to accelerate forest regeneration by suppressing weeds and attracting seed dispersers), in a restoration trial in northern Thailand. The goal was to enable restoration practitioners to factor in carbon sequestration, when selecting tree species to plant. Above-ground carbon sequestration was derived from wood density, tree volume and above-ground biomass of 3 trees of each of 12 tree species, in 5, 10 and 14-year old restoration plots (RF5, RF10 and RF14, respectively). Wood density did not vary significantly with tree age (p ≤ 0.05), but it did differ significantly among tree species (p ≤ 0.05). Gmelina arborea wood was the densest (0.57 ± 0.10 g/cm3). Carbon concentration of stem wood did not vary significantly among tree species or age (p ≤ 0.05), averaging 44.67% (±0.54). Tree volume varied among the species in the youngest plot, but such variation declined with tree age. In the oldest plot (RF14), Erythrina subumbrans and Spondias axillaris grew significantly larger than the other species and sequestered the most above-ground carbon: 135.23 and 115.87 kgC/tree respectively. Bischofia javanica sequestered the least, only 9.80 kgC/tree. An even framework species mix would sequester 13.2, 44.3 and 105.8 tC/ha, 5, 10 and 14 years respectively after planting and would achieve carbon storage levels similar to those of nearby natural forest in 16 - 17 years. The framework species method is therefore capable of rapidly accumulating carbon, a property which, along with its acceleration of biodiversity recovery and provision of a wide range of forest products and ecological services to local people, meets both the requirements and safeguards of REDD+ projects.
Highlights
Tropical forests are a major terrestrial sink for atmospheric CO2, absorbing about 18% of anthropogenic emissions (IPCC, 2000)
Early pioneer species tended to have lower wood density than later succession species, agreeing with other authors (e.g. Henry et al, 2010), but Gmelina arborea and Prunus cerasoides were notable exceptions having higher than expected wood density for pioneer tree species
When implementing forest restoration for carbon sequestration, such as for REDD+ projects, it is tempting to maximize carbon absorption by planting one or a few of the top carbon-storing tree species, since the funding of such projects is linked to how much carbon is se
Summary
Tropical forests are a major terrestrial sink for atmospheric CO2, absorbing about 18% of anthropogenic emissions (IPCC, 2000). From 2005 to 2010, tropical forest carbon stocks decreased by approximately 0.5 GtC/year (FAO, 2010). From 1980 to 2005, tropical forest cover declined from 19.7 to 17.7 million km (−0.37% per year), contributing 6% - 17% towards total anthropogenic greenhouse gas emissions (Scharlemann et al, 2010). Reforestation in the tropics could increase the carbon sink and remove substantial amounts of CO2 from the atmosphere. Just 3 years later, at the 2014 UN Climate Summit, the New York Declaration on Forests increased this target to 350 million hectares by 2030, which would sequester an estimated 1.7 GtC/year; a substantial contribution towards climate change mitigation (Bonn Challenge, 2011)
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