Reforestation can sequester two petagrams of carbon in US topsoils in a century - PubMed (original) (raw)

Reforestation can sequester two petagrams of carbon in US topsoils in a century

Lucas E Nave et al. Proc Natl Acad Sci U S A. 2018.

Abstract

Soils are Earth's largest terrestrial carbon (C) pool, and their responsiveness to land use and management make them appealing targets for strategies to enhance C sequestration. Numerous studies have identified practices that increase soil C, but their inferences are often based on limited data extrapolated over large areas. Here, we combine 15,000 observations from two national-level databases with remote sensing information to address the impacts of reforestation on the sequestration of C in topsoils (uppermost mineral soil horizons). We quantify C stocks in cultivated, reforesting, and natural forest topsoils; rates of C accumulation in reforesting topsoils; and their contribution to the US forest C sink. Our results indicate that reforestation increases topsoil C storage, and that reforesting lands, currently occupying >500,000 km2 in the United States, will sequester a cumulative 1.3-2.1 Pg C within a century (13-21 Tg C·y-1). Annually, these C gains constitute 10% of the US forest sector C sink and offset 1% of all US greenhouse gas emissions.

Keywords: greenhouse gas; land use; management; mitigation; soil carbon.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Cultivation is a land use with strong impacts on land cover and soil morphology that are readily recognized in remote sensing products (NLCD) and soil observation datasets (ISCN). By recognizing the distinctive Ap horizon (plow layer) as a legacy of past cultivation, lands currently possessing forest cover can be separated into two groups: natural forest on never-cultivated soil and forests that are in the process of establishing on previously cultivated soil. Collectively, these three groups represent a forest-to-cultivation-to forest transition that is playing out over hundreds of thousands of square kilometers in the United States.

Fig. 2.

Cultivated soils are clay-rich, forests persist on sandy and stony soils, and reforestation tends to happen on marginal soils of intermediate textures. Graphs show the percentage clay, sand, and stone contents of topsoil horizons from cultivated, reforesting, and natural forest ISCN-NLCD sites (n = 12,617). Boxes are medians and 25th and 75th percentiles; whiskers are 10th and 90th percentiles; dots are fifth and 95th percentiles. Medians are significantly different (P < 0.05) for all three land use groups except in the case of sand content (no significant difference between cultivated and reforesting).

Fig. 3.

Topsoil C stocks are least under cultivation, greatest in natural forest, and intermediate on reforesting soils (Left); soil C stocks to 30 cm only differ significantly between cultivated and natural forest land uses (Right). Data are from ISCN-NLCD sites (n = 12,617). See Fig. 2 for box, whisker, and dot information. Within each depth, superscripts denote significant differences (P < 0.05) in median C stocks between land uses. The dotted lines in each figure are intended to aid in visual reference and show thresholds that are 5%, 50%, or 100% greater than cultivated baseline levels.

Fig. 4.

Differences in topsoil C storage among cultivated, reforesting, and natural forest ISCN-NLCD sites are consistent across ecoregions (total n = 12,238). Plot shows the mean and SE for each ecoregional division and land use. Annotations at left indicate significance of multiple comparisons (P < 0.05) among abbreviated land uses (C, cultivated; NF, natural forest; RF, reforesting).

References

1. Griscom BW, et al. Natural climate solutions. Proc Natl Acad Sci USA. 2017;114:11645–11650. -PMC -PubMed
1. Minasny B, et al. Soil carbon 4 per mille. Geoderma. 2017;292:59–86.
1. Follett RF. Beyond mitigation: Adaptation of agricultural strategies to overcome projected climate change. In: Liebig MA, Franzluebbers AJ, Follett RF, editors. Managing Agricultural Greenhouse Gases: Coordinated Agricultural Research through GRACEnet to Address Our Changing Climate. Elsevier; New York: 2012. pp. 693–718.
1. Poeplau C, Don A. Carbon sequestration in agricultural soils via cultivation of cover crops—A meta-analysis. Agric Ecosyst Environ. 2015;200:33–41.
1. Jobbagy EG, Jackson RB. The vertical distribution of soil organic carbon and its relation to climate and vegetation. Ecol Appl. 2000;10:423–436.

Reforestation can sequester two petagrams of carbon in US topsoils in a century - PubMed (original) (raw)