Stand structure and carbon storage of a young mangrove plantation forest in coastal area of Bangladesh: The promise of a natural solution

Abstract

Globally, with the growing importance of mangroves for providing ecosystem services and mitigating climate change, it is still uncertain whether planted mangroves can be the counterpart of natural mangroves, and thus the role of planted mangroves is still less understood. Therefore, this study aimed to assess the stand structure and carbon storage of a young mangrove plantation in Satkhira District, Bangladesh and to compare it with the natural mangrove forest (i.e., Sundarbans) to understand the potential of this young mangrove plantation as a nature-based solution to climate change. In addition, to better understand the spatial dynamics of afforested mangrove forests, we investigated and compared both above and below-ground carbon stocks between the landward and riverward sites. We collected both above (height and diameter at breast height, DBH) and belowground (i.e., coarse and fine root) data from 16 plots with a total area of 1600 m2 in two paired transects, eight plots each in landward and riverward sites. Aboveground carbon stocks were estimated using the species-specific allometric models from the biophysical tree parameters (i.e., height and DBH). Besides, belowground root (≥ 20 mm) carbon was measured by direct weighting after collecting soil samples through coring. Stand structural attributes (i.e., density, basal area, and DBH) showed a significant difference between the two sites, whereas Sonneratia apetala was found as the dominant species (IV = 188.7∼207.1) in both forest sites. The mean carbon stock of this plantation was 49.1 Mg C ha−1, while the mean aboveground carbon (AGC) was 37.3 Mg C ha−1. The landward site contributed significantly more AGC (40.1 Mg C ha−1) than the riverward (34.4 Mg C ha−1) site (p<0.05). Besides, the mean belowground roots carbon (BGRC) of this plantation was 11.8 ± 1.4 Mg C ha−1, where the riverward site contributed significantly more root carbon (14.3 Mg C ha−1) than the landward site (9.4 Mg C ha−1) (p<0.05). Tree density and basal area showed a significant positive relationship with BGRC. Although only two species were planted, after 15 years, we observed the total number of species reached nine. The carbon stock, progressive species richness in this plantation reflects the significance of young mangrove plantations in sequestering carbon to mitigate climate change and biodiversity conservation as nature-based solutions which may be useful for future coastal afforestation and restoration programs.