Long-Term Biomass Recovery and Future Blue Carbon Potential of Indus Delta Mangroves

A research team led by Professor Faming Wang at the South China Botanical Garden, Chinese Academy of Sciences, has reconstructed the long-term dynamics of above-ground biomass in the Indus Delta mangroves and evaluated their potential changes through 2050. The findings provide new evidence for the recovery and blue carbon potential of mangroves in arid coastal environments and offer a modelling framework to support mangrove restoration and adaptive management.

The study, entitled “Spatiotemporal dynamics and machine learning-based prediction of above-ground biomass in the Indus Delta mangroves,” was published in Functional Ecology, a journal of the British Ecological Society.

Mangroves are highly productive blue carbon ecosystems that remove carbon dioxide from the atmosphere while contributing to shoreline stabilization, protection from coastal hazards and biodiversity conservation. Located along the Arabian Sea coast of Pakistan, the Indus Delta supports one of the world’s largest mangrove systems occurring in an arid climatic region.

The ecosystem is exposed to less than 200 mm of annual rainfall, high evaporation and elevated salinity. It has also experienced substantial pressures from reduced freshwater discharge, declining sediment delivery, land-use change and other human activities. Although large-scale planting and community-based conservation programmes have promoted mangrove recovery in recent decades, the long-term dynamics of mangrove biomass and its future development have remained insufficiently quantified.

To address this knowledge gap, the researchers integrated field-derived above-ground biomass data with multisource remote-sensing, climatic and land-use variables. They compared four machine-learning approaches—random forest, gradient-boosted regression trees, support vector regression, and classification and regression trees—to reconstruct spatial and temporal biomass patterns from 2002 to 2022 and project potential changes for 2030, 2040 and 2050.

The results showed a significant increase in the mean above-ground biomass of the Indus Delta mangroves, from 18.13±9.10 Mg ha⁻¹ in 2002 to 25.75±8.32 Mg ha⁻¹ in 2022. This long-term increase indicates a gradual recovery of mangrove vegetation across the delta.

Among the evaluated algorithms, the gradient-boosted regression tree model produced the best predictive performance, with an R² of 0.65. Under a scenario in which current environmental trends, restoration activities and management conditions are maintained, the model projected that mean above-ground biomass could reach 30.31±4.80 Mg ha⁻¹ by 2030, 40.12±6.40 Mg ha⁻¹ by 2040 and 48.60±7.90 Mg ha⁻¹ by 2050.

The analysis also identified important environmental controls on mangrove biomass. Above-ground biomass was positively associated with remotely sensed vegetation indices but negatively related to land surface temperature and land-use change. These relationships suggest that increasing thermal stress and continued coastal development could constrain biomass accumulation, whereas sustained vegetation recovery, freshwater availability and sediment supply are critical for maintaining mangrove productivity and resilience.

By combining long-term trend analysis, multisource environmental data and comparative machine-learning modelling, the study provides the first spatially explicit reconstruction and forward projection of mangrove above-ground biomass for the Indus Delta. The approach moves beyond static biomass mapping and provides a decision-support framework that could be adapted for biomass monitoring and restoration planning in other climate-sensitive coastal wetlands.

The authors emphasized that the projections represent potential trajectories under the continuation of current trends rather than guaranteed future outcomes. Further research incorporating higher-resolution observations, long-term field measurements, species-specific information, hydrological and sediment dynamics, and socioeconomic scenarios will be required to reduce uncertainty.

For the Indus Delta, maintaining adequate freshwater and sediment delivery, limiting damaging land-use conversion, sustaining restoration programmes and strengthening the participation of local communities will be essential for translating mangrove recovery into durable blue carbon and climate-adaptation benefits.

Dr. Muhammad Naveed, a postdoctoral researcher at the South China Botanical Garden, is the first author of the study. Professor WANG Faming is the corresponding author. The research was conducted in collaboration with researchers from Central South University, the University of Ghana and other institutions.

The work was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, the European Union Horizon Europe C-BLUES project, the Guangdong Science and Technology Program, and the Guangdong Basic and Applied Basic Research Foundation, among other programmes. Article link:DOI: 10.1111/1365-2435.70342.

Figure. Mangrove Biomass C stocks.（Image by WANG Faming）