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Mangrove forests protect tropical coasts from storms, store large amounts of carbon and provide vital habitats for plants and animals, serving for example as nurseries for fish and crabs. They also supply local communities with wood and medicinal plant substances. But how resilient are these ecosystems to increasing environmental pressures? An international research team including the Leibniz Centre for Tropical Marine Research (ZMT) investigated the role biodiversity plays in the resilience of mangrove forests. The study, co-authored by ZMT mangrove ecologist Martin Zimmer, focuses on the Sundarbans, one of the largest contiguous mangrove ecosystems in the world.
The Sundarbans stretch over more than 10,000 square kilometres across Bangladesh and India and are one of the last remaining largely intact mangrove ecosystems. The forests provide habitat for numerous endangered species, such as the Sundari tree, which is characteristic of the region, the endangered Bengal tiger, the saltwater crocodile and the Irrawaddy dolphin. The Sundarbans are recognised as a UNESCO World Heritage Site.
Mangrove forests such as the Sundarbans are exposed to numerous influences, including fires, storms and pathogens, as well as pressures from aquaculture and forestry and the effects of climate change. The ability of an ecosystem to recover from such natural or anthropogenic disturbances is referred to as ecological resilience. It is crucial for the survival and balance of mangrove forests under changing conditions.
The researchers used satellite-based measurements of plant growth (vegetation indices) as well as biodiversity and environmental data to investigate and evaluate the resilience of the Sundarbans and the associated influencing factors. Employing a complex statistical model, they were able to compare the correlation of various metrics for biodiversity and environmental parameters with values for resilience.
+++ Role of species richness and different mangrove species +++
The calculations showed that up to eight environmental stressors affect the ecosystem in the Sundarbans, of which the most relevant are: cyclones, salinity intrusion, heat stress and reduced freshwater flow during droughts.
The resilience of mangrove forests to such disturbances and stressors varied depending on the area and zone. But overall, 10 to 15 percent of the total Sundarbans have lost resilience in recent decades, according to the researchers' findings.
In order to better counteract such resilience loss in the future, the researchers wanted to understand what role species richness or the presence of different mangrove species play in resilience.
Martin Zimmer and his co-authors found a pattern that they had found before in the context of biodiversity as a driver of ecosystem processes and properties: “According to our analyses, the mere number of species, often referred to as species richness, plays a minor role when it comes to predicting the resilience of mangrove forests,” the mangrove researcher says.
“Functional and structural diversity, for example how varied and complex a mangrove forest is in terms of tree height, density, spatial arrangement and root shape, has a greater influence on the resilience of the ecosystem. The contribution of species diversity is therefore more indirect, via the functional and structural differences between various mangrove species,” Zimmer explains.
+++ New impetus for mangrove protection +++
Last week, Germany acceded to the Marine Biodiversity Convention (BBNJ), which was ratified by the United Nations at the beginning of the year. The convention includes the so-called 30x30 target, according to which at least 30 per cent of marine and terrestrial areas worldwide should be effectively protected by 2030.
Based on their analyses, the researchers are now formulating new recommendations to specifically strengthen the resilience of mangrove forests and coastal communities that depend on them for their livelihood and wellbeing to climate change effects, thereby protecting these ecosystems in line with the 30x30 target.
Martin Zimmer: “Instead of simply increasing the number of different species when protecting or (re-)establishing mangrove forests, such efforts should focus on a few location-specific dominant mangrove species and supplement these with functionally distinct species in order to increase structural diversity.”
+++ Ecosystem co-design as an effective concept +++
The concept of ecosystem co-design developed at ZMT could also be applied here, says Zimmer. According to this approach, the targeted (re-)establishment of certain species with suitable characteristics would depend on which properties, processes or services of the ecosystem are desired or needed. “In this case, it's about the resilience of mangrove forests. In earlier studies, we focused on carbon storage or the productivity of mangrove forests,” says the researcher.
Prof. Dr. Martin Zimmer | Head of the Mangrove Ecology working group at the Leibniz Centre for Tropical Marine Research and Professor for Mangrove Ecology an at the University of Bremen
Email: martin.zimmer@leibniz-zmt.de
Rahman MM, Zimmer M, Donato D, Liang J, Khan MNI, Weng Q. 2026. Functional composition and structural diversity enhance mangrove forest resilience in the Sundarbans. Nature Comm Earth Env. https://doi.org/10.1038/s43247-026-03305-5
Mangroves in the Sundarbans in Bangladesh. The Sundarbans cover more than 10,000 square kilometres a ...
Copyright: Photo: Martin Zimmer, Leibniz Centre for Tropical Marine Research (ZMT)
The mangrove forests of the Sundarbans provide habitat for numerous species.
Copyright: Photo: Martin Zimmer, Leibniz Centre for Tropical Marine Research (ZMT)
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Mangroves in the Sundarbans in Bangladesh. The Sundarbans cover more than 10,000 square kilometres a ...
Copyright: Photo: Martin Zimmer, Leibniz Centre for Tropical Marine Research (ZMT)
The mangrove forests of the Sundarbans provide habitat for numerous species.
Copyright: Photo: Martin Zimmer, Leibniz Centre for Tropical Marine Research (ZMT)
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