A. Along tropical and subtropical coastlines, where rivers meet the sea, grow forests unlike any others. Mangroves are trees and shrubs that can survive in salty water and in mud that is flooded twice a day by the tide. They are found in more than 100 countries, with some of the largest areas in Indonesia, Brazil and Australia, and they include around 70 species that belong to several unrelated plant families. What unites them is a set of adaptations to one of the harshest environments on Earth.
B. The first challenge is salt. Some mangrove species prevent most salt from entering their roots through a kind of filtering process; others absorb salt but get rid of it through special glands on their leaves, which can sometimes be seen covered in white crystals. The second challenge is a lack of oxygen, because waterlogged mud contains very little air. Many mangroves solve this problem with aerial roots: some send up pencil-like roots that stick out of the mud, while others develop arching 'stilt' roots that support the trunk above the water. These structures contain small pores through which the plant can take in air at low tide.
C. Mangroves also have an unusual way of reproducing. In several species, seeds begin to grow while still attached to the parent tree, producing long, spear-like seedlings. When they drop, some plant themselves in the mud below, while others float away on the tide. These floating seedlings can survive in seawater for months, allowing mangroves to colonise distant shores. This strategy gives the young plants a head start in an environment where ordinary seeds would struggle to take root.
D. For coastal communities, mangroves provide a range of valuable services. Their dense roots slow down waves and trap sediment, protecting shorelines from erosion and reducing the damage caused by storms. Studies after the Indian Ocean tsunami of 2004 suggested that, in some places, villages behind healthy mangroves suffered less damage than those without such protection, although the size of this effect remains debated. Mangroves also serve as nurseries for many species of fish and shellfish, whose young shelter among the roots before moving out to sea, supporting local fisheries.
E. In addition, mangroves are remarkably effective at storing carbon. Because their waterlogged soils contain little oxygen, dead leaves and roots decompose very slowly, and carbon can build up in the mud over thousands of years. Per hectare, mangrove forests store considerably more carbon than most tropical forests on land, which is why they have attracted interest as a tool for tackling climate change.
F. Despite their value, mangroves have been lost at an alarming rate. Over recent decades large areas have been cleared for shrimp farms, rice fields, tourism and coastal development. The rate of loss has slowed since the early 2000s, and many countries have launched replanting programmes. However, experts warn that replanting is not always successful: seedlings are sometimes planted in places where mangroves never grew naturally, and many die. Protecting existing forests, they argue, is usually cheaper and more effective than trying to restore them once they have gone.