Mangroves: growth has outpaced loss worldwide since 2010
· BehindLines newsroom
After decades of decline, mangrove forests are regaining ground around the world. According to NASA's Earth Observatory, a study published in Science and based on Landsat satellite images shows a turnaround around 2010. Yale Environment 360 magazine also reports gains, based on an analysis of satellite images published in the same journal in June.
Forty years of satellite images
According to NASA, the researchers analysed Landsat images from 1984 to 2023 to track the extent and density of the mangrove canopy. They count nearly 3,000 km² lost between 1984 and 2010, then an unexpected rise of about 2,000 km² after that date, mostly in the regions of Asia, Australia and South America. For 2010-2023, Yale Environment 360 reports about 3,200 square miles of growth against some 2,400 square miles of losses, and writes that worldwide cover is back at the level of the 1980s. The two outlets do not cover the same periods and do not use the same units; we do not convert them.
Where and why
Zhen Zhang, of Tulane University, quoted by NASA, estimates that two-thirds of the expansion comes from the colonisation of new areas and one-third from the restoration and regrowth of degraded zones. In Myanmar (Burma), NASA says the country lost 28.6% of its mangroves between the 1980s and 2010, and that their area has since grown by about 10%. The study's authors attribute this reversal to greater awareness and restoration efforts after the 2004 tsunami, to stronger legal protection of the forests and to heavy sedimentation that opened up new mudflats. Yale Environment 360 notes that Indonesia has been stable since 2005 and that Southeast Asia accounts for more than 40% of global gains since 2010.
Limits
The gains are not universal: according to NASA, losses in the Niger Delta have reduced the area in West and Central Africa, and cyclones have degraded vast zones of North America and southern Africa. Pete Bunting, of Aberystwyth University, quoted by Yale Environment 360, acknowledges that the causes of these gains are not fully understood; the magazine specifies that his mapping cannot tell planted trees from natural regeneration. Ecologist Norman Duke, of James Cook University, for his part considers that quantity must not be confused with quality.
Why it matters
NASA points out that mangroves hold, at most, four times the carbon of the taller tropical forests found inland, and protect coasts from erosion and storm surges. Zhen Zhang warns against any complacency: in his view, these successes show that conservation and slowing deforestation can have large positive effects when they add to natural expansion and regeneration.