What Grows Back On A Ruined Shore

AFew conservation measures enjoy the political welcome now extended to mangrove planting. The forests that fringe tropical estuaries lock carbon into waterlogged soils at rates several times those of dry woodland, they blunt the surge that arrives with a cyclone, and they can be established, or so the brochures imply, by volunteers with buckets. Between 1996 and 2020 the world lost a little under six thousand square kilometres of mangrove, and the response of governments has been to announce targets counted in seedlings: a hundred million here, a billion there, with the running totals reported to donors each year. The same period has produced a second and far less comfortable literature, assembled by the people sent back to look at the sites afterwards. Its finding is monotonous. Most of what is planted dies, and it dies within two years, on ground where mangrove was never going to grow. Whether the failure belongs to the engineering of the sites or to the arrangements made with the people who live beside them has become the central dispute of the field.

BNuria Bastida, a coastal geomorphologist at the Estuarine Systems Unit in Cadiz, holds that the arrangements are beside the point until the ground is right. Between 2011 and 2019 her group revisited 74 completed projects in five countries and set each one against tidal records, covering some 2.6 million seedlings in all. Median survival five years after planting was 14 per cent. Across the same period the number of seedlings put into the ground each year in the region roughly tripled, an expansion that reads in donor reports as progress. What did not change was the share of sites still carrying forest at year five. The reason, on her account, is legible in the maps rather than in the survival curves: 61 per cent of the projects had been planted on open mudflat below the elevation at which mangrove establishes anywhere on that coast, ground that stands under water for too many hours a day for a seedling to breathe. Sites, she notes, had been chosen for accessibility rather than for tidal elevation, since a shore a boat can reach is a shore a minister can visit.

CThe account yields a prediction, and Bastida has tested it. If elevation and drainage set the limit, a shore whose water flow is repaired should recover with no planting at all. At 18 places where colonial-era embankments were breached and tidal creeks reopened, seedling density four years later reached a median of 4,200 per hectare, against 900 at planted sites of comparable exposure. Regeneration was confined to shores lying within about two kilometres of a surviving stand; past that distance, breaching the embankment produced bare mud and nothing else. The asymmetry is awkward for the industry, since the cheap intervention is the one that works. Bastida nonetheless presents hydrological repair as a precondition for planting rather than as a replacement for it, and where the ground already sits at the right height she accepts that what happens next is not a question hydrology can answer.

DChidi Nwankwo, who studies resource governance at the Bight of Benin Coastal Institute, answers that a plantation lost on suitable ground is telling you about ownership, not about tides. His survey covered 32 villages on delta shores lying at the elevations where mangrove grows unaided, and it recorded survival at year five of 58 per cent where the community held documented rights over the restored area, against 19 per cent where the shore remained state land that anyone might cut. Arrangements of that kind are now written into several national programmes, although they were distinctly unusual when the survey began. A forest with no owner, Nwankwo argues, is firewood with a delay. He concedes two things. His villages lie within a single delta, and enforcement was judged indirectly, from the cutting incidents that village committees chose to record, because no independent register of them exists.

EThe argument left the seminar room some time ago. Since 2021 the standards used to certify blue carbon credits have required developers to report survival at year five rather than seedlings at year one, and projects unable to produce the figure have had issuance suspended. Bastida points out, uncomfortably for her own position, that reopening a creek yields no row of seedlings for an auditor to photograph, so the measure with the best record is the one hardest to sell. Nwankwo replies that this appetite for visible effort is precisely what keeps villages out of the accounts, since a right of tenure photographs no better than a tide does. Both regret one habit above all: that the field goes on reporting seedlings planted instead of hectares still forested, a practice that flatters every party to it.

FA settlement of sorts is emerging in which the two accounts are assigned to different stages rather than ranked against each other. Where the ground lies below the tidal range, no amount of local involvement will keep a plantation alive and the site should never have been chosen; where the physical setting is suitable, survival turns instead on who holds a claim to the trees and who loses by their removal. The unresolved question is whether a restored forest comes to store carbon at the rate of an undisturbed one across the decades that credits are sold against, and no series of measurements yet runs long enough to settle it. What both researchers reject is the assumption that produced the targets in the first place, namely that a coastline can be repaired by counting the things that are put into it.