Mangroves among the most carbon-rich forests in the tropics

Journal name:
Nature Geoscience
Volume:
4,
Pages:
293–297
Year published:
DOI:
doi:10.1038/ngeo1123
Received
Accepted
Published online

Mangrove forests occur along ocean coastlines throughout the tropics, and support numerous ecosystem services, including fisheries production and nutrient cycling. However, the areal extent of mangrove forests has declined by 30–50% over the past half century as a result of coastal development, aquaculture expansion and over-harvesting1, 2, 3, 4. Carbon emissions resulting from mangrove loss are uncertain, owing in part to a lack of broad-scale data on the amount of carbon stored in these ecosystems, particularly below ground5. Here, we quantified whole-ecosystem carbon storage by measuring tree and dead wood biomass, soil carbon content, and soil depth in 25 mangrove forests across a broad area of the Indo-Pacific region—spanning 30° of latitude and 73° of longitude—where mangrove area and diversity are greatest4, 6. These data indicate that mangroves are among the most carbon-rich forests in the tropics, containing on average 1,023Mg carbon per hectare. Organic-rich soils ranged from 0.5m to more than 3m in depth and accounted for 49–98% of carbon storage in these systems. Combining our data with other published information, we estimate that mangrove deforestation generates emissions of 0.02–0.12Pg carbon per year—as much as around 10% of emissions from deforestation globally, despite accounting for just 0.7% of tropical forest area6, 7.

At a glance

Figures

  1. Examples of Indo-Pacific mangroves.
    Figure 1: Examples of Indo-Pacific mangroves.

    The sample included a broad range of stand stature, composition, and soil depth. a, Exemplary large-stature, high-density mangrove dominated by Bruguiera, Borneo, Indonesia (canopy height >15m, canopy closure >90%, soil depth >3m). b, Exemplary small-stature, low-density mangrove dominated by Rhizophora, Sulawesi, Indonesia (canopy height <4m, canopy closure <60%, soil depth 0.35–0.78m). Both estuarine and oceanic mangroves can exhibit both conditions (see Supplementary Table S1).

  2. Comparison of mangrove C storage (mean [plusmn]95% confidence interval) with that of major global forest domains.
    Figure 2: Comparison of mangrove C storage (mean ±95% confidence interval) with that of major global forest domains.

    Mean C storage by domain was derived from ref. 9, including default values for tree, litter, dead wood, root:shoot ratios, and soils, with the assumption that the top 30cm of soil contains 50% of all C residing in soil9, except for boreal forests (25%). Domain means are presented for context; however some forest types within each contain substantially higher or lower C stores9, 10. In general, the top 30cm of soil C are considered the most vulnerable to land-use change9; however in suboxic peat/muck soils, drainage, excavation, and oxidation may influence deeper layers29.

  3. Above- and below-ground C pools in Indo-Pacific mangroves, assessed by distance from the seaward edge.
    Figure 3: Above- and below-ground C pools in Indo-Pacific mangroves, assessed by distance from the seaward edge.

    a, Estuarine mangroves situated on large alluvial deltas. b, Oceanic mangroves situated in marine edge environments—for example, island coasts. Below-ground C comprised 71–98% and 49–90% of ecosystem C in estuarine and oceanic sites, respectively. Overall carbon storage did not vary significantly with distance from the seaward edge in either setting over the range sampled (P>0.10 for above-ground, below-ground, and total C storage by functional data analysis (FDA, see Methods); 95% CIs for rates-of-change all overlapped zero and were between −1.2 and 3.9MgCha−1 per metre of distance from edge).

  4. Soil properties determining below-ground carbon storage in Indo-Pacific mangroves.
    Figure 4: Soil properties determining below-ground carbon storage in Indo-Pacific mangroves.

    a, Soil C concentration was greater in oceanic (mean=14.6%) versus estuarine (mean=7.9%) sites (P=0.001), and decreased with depth (P<0.0001; effect stronger in oceanic sites). Change in C concentration with seaward distance was biologically insignificant. b, Soil bulk density did not differ significantly with setting (P=0.79); hence one line is shown combining both settings. Bulk density increased with depth (P<0.0001) but not seaward distance (P=0.20 ), and a distance*depth interaction term was not significant (P=0.47). c, Soil depth increased with distance from the seaward edge in oceanic stands (FDA result: P=0.002, 95% CI for rate-of-change = 21–65cm increase per 100m distance).

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Affiliations

  1. USDA Forest Service, Pacific Southwest Research Station, 60 Nowelo St., Hilo, Hawaii 96720, USA

    • Daniel C. Donato
  2. USDA Forest Service, Northern Research Station, 271 Mast Rd., Durham, New Hampshire 03824, USA

    • J. Boone Kauffman
  3. Center for International Forestry Research (CIFOR), PO Box 0113 BOCBD, Bogor 16000, Indonesia

    • Daniel Murdiyarso &
    • Sofyan Kurnianto
  4. USDA Forest Service, International Programs, 1099 14th street NW, Suite 5500W, Washington, District of Columbia 20005, USA

    • Melanie Stidham
  5. Viikki Tropical Resources Institute (VITRI), University of Helsinki, PO Box 27, FIN-00014, Finland

    • Markku Kanninen

Contributions

D.C.D. co-designed the study, collected field data, performed data analyses, and led the writing of the paper. J.B.K. conceived and co-designed the study, and contributed to data collection and writing. D.M. co-conceived the study, arranged for and contributed to data collection, and contributed to writing. S.K. contributed to data collection, data analysis, and writing. M.S. collected field data and contributed to writing. M.K. co-conceived the study and contributed to writing.

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The authors declare no competing financial interests.

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