Rethinking global carbon storage potential of trees. A comment on Bastin et al. (2019)
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OPINION PAPER
Rethinking global carbon storage potential of trees. A comment on Bastin et al. (2019) Shawn D. Taylor 1,2
&
Sergio Marconi 1
Received: 4 October 2019 / Accepted: 10 January 2020 # This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2020
Abstract & Key message Bastin et al. 2019 use two flawed assumptions: 1) that the area suitable for restoration does not contain any carbon currently, and 2) that soil organic carbon (SOC) from increased canopy cover will accumulate quickly enough to mitigate anthropogenic carbon emissions. We re-evaluated the potential carbon storage worldwide using empirical relationships of tree cover and carbon. We use global datasets of tree cover, soil organic carbon, and above ground biomass to estimate the empirical relationships of tree cover and carbon stock storage. A more realistic range of global carbon storage potential is between 71.7 and 75.7 GtC globally, with a large uncertainty associated with SOC. This is less than half of the original 205 GtC estimate. The potential global carbon storage of restored forests is much less than that estimated by Bastin et al. 2019. While we agree on the value of assessing global reforestation potential, we suggest caution in considering it the most effective strategy to mitigate anthropogenic emissions. A preprint version of this article was published on 13 August 2019 at https://doi.org/10.1101/730325
1 Main Bastin et al. (2019) (hereafter referred to as Bastin 2019) use a novel machine learning based method to model global tree canopy cover potential. After accounting for current tree canopy cover and areas already occupied by urban and agricultural land, they estimate 900 Mha of potential tree canopy cover available worldwide for reforestation. Using biome Handling Editor: Erwin Dreyer Contribution of the co-authors ST conceived of the idea and performed the analysis. ST and SM wrote the manuscript. A preprint version of this article was published on 13 August 2019 at https://doi.org/10.1101/730325 * Shawn D. Taylor [email protected] Sergio Marconi [email protected] 1
School of Natural Resources and Environment, University of Florida Gainesville, Gainesville, FL, USA
2
U.S. Department of Agriculture, Agricultural Research Service, Jornada Experimental Range, New Mexico State University, Las Cruces, NM, USA
specific estimates of tonnes C per hectare they calculate the global carbon storage potential of this 900 Mha of tree canopy cover. The tonnes C per hectare values for each biome are derived from average estimates of total carbon storage from two studies of forest (Pan et al. 2011) and tropical grassland (Grace et al. 2006) carbon stock. Thus from their calculation, a hectare of restored tree canopy is equivalent to adding a full hectare of carbon stock potential regardless of the vegetation already in place and results in an overestimate of the global carbon stock potential of restored trees. To better estimate the relationship between to
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