Discover how mangroves fight climate change and protect the land while taking care of the sea…
Do you know the mangrove, this coastal forest of tropical areas ? Do you know what role it plays in the conservation of coastal ecosystems exposed to cyclones and rising waters ? Even if the world’s mangroves host about sixty varieties of trees, in general only 3 or 4 species coexist on the same site. What then explains the extreme importance of this kind of forest at the global level and the urgency to protect it ?
For this first article in the « Forest of the World » series, I take you to explore the mangrove of southern Martinique in the West Indies.
The mangrove of the Salines Regional Natural Park, in the south of Martinique, is a popular place for hiking and walking. So appreciated that the magnificent beach of the Salines receives nearly 1 million visitors per year ! However, tourism is not the only threat to this fragile environment as we will see in the rest of this article.
On commence l’approche par une forêt côtière sèche composée principalement de mancenilliers toxiques, de raisiniers et de cocotiers. Ce type de boisement se retrouve sur d’autres sites de l’île comme par exemple à Tartane. Un peu plus loin, vers la savane des pétrifications, le cordon littoral se retrouve pris en étau entre l’océan et le lac des Salines. À cet endroit commence le royaume des palétuviers.
The 5 major benefits of mangroves
Here are in 5 points the totally free benefits of the mangrove in our lives. Yes, I know, in a mercantile society it seems completely crazy!
- An ecological niche
- An incredibly efficient carbon sink
- A rampart against storms and erosion
- A wastewater treatment plant
- Valuable natural resources
All these qualities must alert us to the importance of protecting, regenerating and studying this unique natural environment. There is a lot of talk about the tropical forests of the Amazon or Africa but mangroves really benefit from being known. Let’s take a closer look at each of these 5 points.
Mangrove: an ecological niche
Mangrove play a vital role in maintaining biodiversity. The entangled roots of red mangliers (see below) are all refuges for fish, molluscs and crustaceans. Indeed, this area represents a spawning site for many species of fish and shrimp. Walking on the paths of the PNR des Salines, we observe an incredible amount of crabs.
This giant nursery attracts migratory or sedentary birds. The observation of this natural wealth is a major tourist asset. Moreover, canoe rides are offered in the Lamentin marsh, in the center of Martinique.
The mangrove is a carbon sink
Globally, mangroves occupy about 1.3 million square kilometers. These forests perform several essential functions in maintaining the global ecological cycle and have considerable socio-economic importance for the coastal areas of the planet.
More surprisingly, researchers estimate that on an equal surface, mangrove stores 10 times more carbon! It is estimated that each year, it can store up to 200 tons of carbon per square kilometer. It also neutralizes carbon fumes from the decomposition of organic matter in the marsh. Mangroves therefore play a considerable role in the fight against climate change compared to their surface.
A bulwark against storms and soil erosion
The presence of mangrove marshes protects the coast but also the land located at the back of this special forest. By fixing the mud and sand thanks to their specific roots, these trees prevent erosion by waves, wind and currents. They break the swell that comes to die in the interlacing formed by the arc-shaped roots of the Rhizophoras. During heavy rains, they break the runoff and retain possible landslides.
In the event of marine flooding of the land, it participates in the desalination of the soil. Indeed, mangroves exude salt through the leaves.
The role of mangroves in water filtration
Located between land and sea, the mangrove is a buffer zone between fresh water and the marine environment. Its action makes it possible to filter and retain a large amount of industrial or agricultural chemical pollutants… Up to a certain point! Many sites today suffer from an overdose of chemical cocktails composed of mineral oils, pesticides and agricultural fertilizers.
By their role similar to a wastewater treatment plant, mangroves help protect the coral reef and the quality of coastal waters. In fact, it is a forest that takes care of the sea!
The mangrove is a forest that takes care of the sea
Guillaume d’I Have A Tree
Natural resources from the mangrove
It’s a real paradox! For example, the Saline mangrove in Martinique is composed of only 4 tree species. From a biological point of view, it is very weak. Yet the mangrove is an extremely rich and productive environment. Fish, crustaceans, molluscs, woods… The populations that live on the outskirts of these areas derive a good part of their livelihood. I remember picking mangrove oysters with the Bijogos in Guinea-Bissao when I was a teenager. The oysters grew in clusters on the aerial roots of the red mangroves. It was an easily accessible and abundant source of food.
Fisheries depend on the productivity of the mangrove. The degradation of one of these swamps directly affects the volume of shrimp, crab and fish fisheries. Obviously, it is local artisanal fishing that suffers first.
The foliage of certain species of mangroves such as Conocarpus erectus (grey mangrove) is a forage supplement easily available in all seasons for buffaloes.
The mangrove wood is of high quality, dense and resistant to the salty environment. It is an excellent fuel used to make charcoal. The largest trunks are sometimes exploited for the construction of stilts or crafts. The bark of some varieties contains many tannins useful for tanning skins. However, it is better not to cut them. This type of forest is difficult to exploit and its regeneration is complex.
The different types of mangroves
Located in the tidal swing zone, mangroves have adopted unique strategies to adapt to this complex, even hostile environment. These trees are said to be « halophyles » because they resist very high salinities. Each species of mangrove grows in a particular area of the mangrove, depending on its distance from the coastline.
Mangroves are usually formed by a fairly small variety of plants, some of which grow at a height of up to 20 m. These forests develop in salt water and are connected to river networks, while providing protection against coastal erosion and storms. We distinguish 3 zones with their particular tree species.
1/ The coastal area or estuaries
It is the first plant curtain between the water of the river or the sea and the land. It is recognized by the interlacing of the roots of red mangroves (Rhizophora mangle). Their challenge is to settle in a very unstable sandy or muddy sedimentary substrate. Thanks to their arc-butting roots, they advantageously distribute their anchor points. In addition, the large aerial surface of the roots of this species allows it to breathe.
The reproduction of the red mangrove is also very surprising. Indeed, it is one of the only plant species whose seed (rhizhome or « plant ») develops directly on the mother plant. When the seedling has roots and a small hops, it detaches. Depending on the tide, either it plants directly at the foot of the mother plant or it drifts for some time before settling further.
2/ The marshy area
Behind the rhizophora, the area is calmer and the water level is very fluctuating. The marsh dries up at low tide. The crabs then take possession of the place. Some fish such as the jumping gobie (periophthalm) resist until the water returns. I remember observing some in a shred of mangrove (the northernmost) in Mauritania, south of the Arguin Bank. It was near this place that the « Medusa » ran aground, inspiring the famous painting by Géricault.
In short, let’s go back to the Salines, Martinique. In this part of the mangrove grow black mangroves (Avicennia germinans). As it is often a stagnant water environment, these plants have developed another strategy to develop. Their roots do not form bows but emerge from the ground like so many small stalagmites. They are called « tymatophores ». These small hollow tubes flush with the surface of the water to supply the plant with oxygen.
Their reproduction is ensured by the multitude of small seeds that fall at the foot of the mother plant. The seedlings develop in a colony between the pneumatophores (see photo).
3/ The semi-dry area
At the back of the mangrove when you come from the sea there is a buffer zone that receives more or less fresh water from runoff while often saturated with salt. In this part, the challenge is to resist extreme salt levels alternating with the arrival of fresh water. All mangroves are « halotolerant », that is, they resist the infernal salt level in the middle. These trees remove salt through the leaves. Moreover, the very name of the place in Martinique comes from this presence that was once exploited in marshes: salt pans.
White mangroves (Laguncularia racemosa) and grey (Conocarpus erectus) bloom in this part of the mangrove.
Protect mangroves around the world
Mangroves provide essential habitats for marine biodiversity. They play a major role in the restoration and conservation of coral reefs and marine ecosystems that depend directly on the establishment of mangroves for their survival. Indeed, sandbanks provide protection (filter) not only against currents, but also against all kinds of pollutants. Mangroves are also home to a multitude of rare terrestrial species, such as some bat species that are threatened by the continuous destruction of their habitat.
>Reduction of waste discharges in coastal areas
The massive discharge of organic and inorganic waste into coastal areas has a considerable negative impact on marine ecosystems. Phytosanitary chemicals, wastewater, plastics, road runoff are particularly dangerous for the health of mangroves and marine ecosystems. We must reduce these releases by collecting, recycling or composting as much as possible and avoiding the excessive use of chemical fertilizers. Using natural wood protection products and methods, such as those of Sol-éco, help reduce the use of petroleum derivatives that always end up in the oceans.
>Participation in the protection and restoration of mangrove forests
Participation in sustainable management projects is crucial for the conservation of mangrove forests. These projects generally include the reforestation and sustainable development of coastal environments, as well as the control of human activities that damage the habitat of mangroves. Collective intervention is essential to allow participation in initiatives such as financing and support for research on the management and impact of mangrove forests for the well-being of the planet.
With Sol-éco, our natural wood protection company, we have contributed to the replanting of Southeast Asian mangroves damaged by a tsunami.
Conclusion
Mangrove forests play an essential role in the ecosystem and the maintenance of the global ecological cycle. They provide not only considerable ecological but also socio-economic benefits for coastal communities, by providing shelter and a source of food to a multitude of marine species. They also contribute to reducing the health risks associated with marine pollution.
Collective action is clearly essential to preserve these precious ecosystems. Everyone must be aware of the important role they play in the health and well-being of our planet and take measures to protect carbon storage and coastal areas. Public awareness is essential. If you are traveling to a mangrove area such as the Salines or Lamentin in Martinique, find out about the proposed visits. It is by knowing them better that you will protect them better!
Guillaume for I Have a Tree
PS : This post is a translation of the original french version already published here.