“Mangrove is a forest that grows in coastal areas of tropical and subtropical areas“, François Fromard, director of research at CNRS, describes for AFP. Acting as a buffer between marine and terrestrial ecosystems, its survival depends on its ability to effectively convert salt water to fresh water. In a study published in the review The nature of communicationa team of researchers, in partnership with Florida International University and NASA, studied the decline of this amazing ecosystem.
Mangroves, a phenomenal carbon sink
Mangroves are mostly made up of trees with long roots and a dense, fast-growing tree, called mangroves. It is precisely because of these characteristics that carbon sinks (CO₂) are spectacular. In fact, their carbon storage is three to five times greater than that in other forests. Australian biochemist Daniel M Alongi, in his book Carbon sequestration in mangrove forests, published in 2012 by an international publishing house Taylor and Francis, explains that mangroves absorb 13.5 gigatons (Gt) of CO₂ each year, or 14% of ocean sequestration.
Mangroves originate from strong litter (leaves, branches and dead trunks), part of which is covered with sediment or crustaceans.
Carbon trapped in ocean sediments can be stored for centuries, even millennia, according to Justine Delangue, project manager of the International Union for Conservation of Nature (IUCN). For example, some mangroves in Indonesia store more than 1,000 tons
Mangroves, natural barriers against storms
Mangroves also significantly reduce the impact of hurricane winds and act as a barrier against storms (mitigating the effects of waves and wind and stabilizing sediments). In the United States alone, mangroves prevent $ 11.3 billion in property damage and 14,200 km2 of flooding each year, and the greatest benefits of flood protection occur during cyclones, according to assistant professor David Lagomasin, lead author of the study.
However, sometimes storms are stronger than mangroves. Using an aerial lidar – used to determine the distance of an object – and satellite images collected before and after Hurricane Irma, researchers behind the study estimated that 62% of mangroves in southwest Florida suffered damage to the canopy (tree top), with the greatest impacts in high forests ( over 10 meters high). At well-drained sites, 83% of mangroves sprouted new leaves within a year of the storm. In contrast, poorly drained inland areas have suffered the largest mangrove degradation ever recorded, covering 10,760 hectares – the equivalent of more than 24,000 football pitches.
Limited elastic capacity: storm surges and rising landscapes
The ability of mangroves to withstand the harsh conditions of cyclones depends on the shape of their soil shape and the elasticity of the plants that make them up. Mangrove that withers also poses a risk of food shortages for populations that depend on it. In fact, mangroves are a great reservoir of animal biodiversity: fish, mollusks, crabs, birds and mammals. They serve as a nursery and refuge for many species, and themselves serve as a source of food for people living nearby.
Damage of climatic origin is added to the damage generated by the anthropogenic (human) footprint. “Artificial obstacles, as well as natural changes in topography, can affect water flow in an area“, states the first author of the study. He adds that”these results are important not only for storm planning in Florida, but also in other coastal states like North Carolina“.
The height of the landscape, the connection of water through the landscape and the height of storm surges (very high waves and high water levels) are indicators of vulnerability. Fact, “low-growing areas that are isolated or do not have the ability to drain after a flood are more likely to experience long-term damage“, the study points out. The latter proposes changes to improve coastal resilience in the event of severe weather. These measures include taking into account storm surges, identifying physical processes and biological resources in lower areas, as well as monitoring drainage basins and improving water connectivity.
Thus, the study concludes that “the bottom is that intense winds cause great damage during hurricanes. However, the intensity of the damage does not have to match the ability of the system to recover over time. Other factors, such as slight changes in the altitude of the coastal landscape and storm surges, play an important role in the way the ecosystem recovers or after it after initial damage. Keeping these factors in mind before the hurricane season can help reduce long-term impacts on vulnerable communities. “ Taking these factors into account would therefore be a way of preventing the deterioration of this essential ecosystem that provides ecological, health, economic and cultural services.