Mangrove forests can rebound thanks to climate change – it’s an opportunity we must take

This article by Christian Dunn, Senior Lecturer in Zoology at the School of Natural Sciences is republished from The Conversation under a Creative Commons license. Read the original article.

Humans have become adept at destroying natural habitats. Indeed, we’re so good at it we’ve changed the very makeup and climate of our planet. But there may be signs the natural world is fighting back by protecting itself against rising temperatures and changing weather patterns, and we face the tantalising prospect of helping this process.

A recent study found that mangrove forests could be adapting to climate change by growing beyond their usual range. The risk of several days of continuous frost, which previously kept these trees in tropical and subtropical areas near the equator, is continuously shifting towards the poles. As average global temperatures rise, mangroves are able to increase their growth and expand their range beyond the equator.

Mangrove forests are coastal wetlands made up of a dense jumble of trees and shrubs capable of living in salt or brackish water. Famous for their tangle of roots sticking up from the ground and dropping down from branches, mangrove forests can grow out into the sea and create almost impenetrable mazes of narrow channels along shorelines.

Mangroves protect coastlines, treat polluted waters, provide livelihoods and resources for some of the world’s poorest people and are home to an impressive number of species – many of which are commercially important. It’s been suggested that the majority of the global fish catch relies, either directly or indirectly, on mangroves.

Despite their value, humans have also done an impressive job over the last century of destroying them to make way for coastal developments, aquaculture and by logging them for timber and fuel production. Not to mention destroying their natural water courses and polluting the ground they grow in.

So the possibility that climate change could be benefiting these habitats is promising indeed. In the long run, this could help society adapt to climate change and even reduce the concentration of greenhouse gases in the atmosphere.

One feature of mangroves that we’ve long benefited from is the protection they offer to our coastlines. Waves lose their power passing through dense mangrove forests, and they can offer protection from storms, typhoons, hurricanes and tsunamis.

Their mass of roots –- both above and below ground – help to bind and build sediments, meaning mangrove areas can grow vertically, which is a clear asset in the face of rising sea levels. Expanding mangrove forests could therefore help protect us from the devastating effects of extreme weather that become more likely with climate change.

Mangrove forests are also incredibly productive ecosystems, which means that lots of carbon dioxide is taken in and used by the trees and shrubs as they grow. When this organic matter dies, a proportion of it forms the sediment underneath the mangrove forest. As a result, carbon remains trapped as semi-decomposed plant matter, and is unable to re-enter the atmosphere as a greenhouse gas. This ensures mangroves can actually act as giant stores – or sinks - of carbon.

Research suggests that mangroves could be better carbon stores than the coastal habitats they are encroaching on – opening the possibility for mangroves to combat the very causes of global warming. In this way, mangroves act as Earth’s natural defences to climate change –- protecting the planet by striking at the very cause of the problem.

Around the world, some mangrove forests are being given legal protection and large-scale restoration works are taking place with varying degrees of success, as one study in Sri Lanka found.

In America and Australia work is being undertaken to restore areas of mangrove dieback following ill-considered developments and the use of herbicides. Conservationists and academics are researching where mangrove restoration would be most beneficial, and developing the best methods for these projects around the world.

The knowledge that mangroves could both benefit from a changing climate and protect us from some of its worst effects demands a renewed vigour in promoting these wetlands. It also raises a question. Should resources be ploughed into maintaining ecosystems where regional changes in the climate are unlikely to help them prosper? Or should we concentrate our efforts on helping expand habitats that are not only resilient to climate change but can help mitigate climate change itself?

Perhaps it is time to move towards the latter and act as ecosystem physicians, giving healing and healable habitats like mangroves every opportunity to do what they do best.

Publication date: 20 November 2018