Well meant, but often unsuccessful: The “forests on stilts” need our help – but mangrove reforestation projects have so far often resulted in unsuccessful mass plantings, complains an international team of experts. In the future, one should rather rely on the natural regenerative power of the mangroves and where reforestation projects actually make sense, the ecological framework conditions have to be better considered, say the scientists.
The long, exposed aerial roots are their trademark: the 80 different types of mangrove trees grow along many of the world’s tropical coasts and estuaries. Due to their special adaptations, they can withstand salty water, fluctuating water levels and high temperatures and form dense forests. These ecosystems are of far-reaching importance for nature and humans: They provide a habitat for numerous animal species and are the nurseries of important fish species. In addition, they protect the coasts from erosion and make a significant contribution to binding the greenhouse gas carbon dioxide from the atmosphere. But humans have already severely damaged these precious natural areas: in the past 50 years, more than a third of the world’s mangrove forests have been cut down or destroyed. And the stocks are still threatened by aquaculture, agriculture and urban development – around 20,000 hectares are lost every year.
At least one positive trend is emerging: the global protection efforts of the last decades have certainly led to great successes. Loss rates have decreased significantly and efforts are also being made in some areas to restore lost mangrove stocks. However, the “Mangrove Specialist Group” of the International Union for Conservation of Nature (IUCN) is now putting the mass planting of mangrove seedlings, which are often intended to serve this goal, in a critical light.
Big effort – little success
The international experts have published a position paper entitled “Pause before you plant”, which aims to alert decision-makers to problems in mangrove conservation. “In the IUCN mangrove expert group, we have been observing a kind of activism with increasing concern for a long time, which is often associated with mangrove planting. It is of course to be welcomed that something is being done to save mangrove forests, but unfortunately many projects are not crowned with success in the long term, ”says co-author Martin Zimmer from the Leibniz Center for Tropical Marine Research.
According to the experts, the failures have various reasons: Accordingly, the projects for restoration through mass planting are often doomed to failure because important ecological framework conditions are not taken into account. For example, mangroves are planted in locations that are exposed to strong currents so that the young plants that have not yet rooted can be easily washed away. In addition, the choice of species is often problematic: “Mass plantings are very effective in the media, but often only focus on one or two species that are easy to plant,” says Zimmer. “The result is often stocks that do not provide the desired ecosystem processes and services. Often, even less stress-resistant monocultures are created or species that are not indigenous, become invasive and can lead to ecological problems, ”said the scientist.
Better planning is the order of the day!
However, the experts emphasize that they do not want to nip restoration measures in the bud. “Nothing is further from us! On the other hand, our paper is intended to stimulate thought. We would like to see a break in the planning of reforestation beforehand and consider what exactly the goal of the whole thing is and how one can really successfully plant mangroves. Hence the title of the position paper ‘Pause before you plant’ ”, says Zimmer.
“First and foremost, we recommend relying on the natural regenerative power of the mangroves. If we can restore the original environmental conditions, the mangrove can expand again on its own. Where this is not possible or where special ecosystem services are to be achieved, reforestation can be a solution, but only under the right ecological conditions. ”Of course, it is best if the mangroves are not cut down in the first place. “The mature trees are simply irreplaceable,” emphasizes Zimmer.
In conclusion, the scientist once again emphasizes the importance of the mangrove forests for the fight against climate change. It is known that the tidal forests store particularly large amounts of greenhouse gas. “On a global average, the mangroves, to put it mildly, store around two tons of carbon dioxide per hectare in a year – that’s roughly what four cars emit. If you look at the global mangrove population of 15 million hectares, mangroves around the world bind about as much CO2 annually as all motor vehicles in Germany produce in one year, ”says Zimmer.
Source: Leibniz Center for Tropical Marine Research, Position paper of the Mangrove Specialist Group (MSG) of the IUCN