Abstract
Mangroves occur along the coastlines throughout the tropics and sub-tropics, supporting a wide variety of resources and services. In order to understand the responses of future climate change on this ecosystem, we need to know how mangrove species have responded to climate changes in the recent past. This study aims at exploring the climatic influences on the radial growth of Heritiera fomes from a local to global scale. A total of 40 stem discs were collected at breast height position from two different zones with contrasting salinity in the Sundarbans, Bangladesh. All specimens showed distinct tree rings and most of the trees (70%) could be visually and statistically crossdated. Successful crossdating enabled the development of two zone-specific chronologies. The mean radial increment was significantly higher at low salinity (eastern) zone compared to higher salinity (western) zone. The two zone-specific chronologies synchronized significantly, allowing for the construction of a regional chronology. The annual and monsoon precipitation mainly influence the tree growth of H. fomes. The growth response to local precipitation is similar in both zones except June and November in the western zone, while the significant influence is lacking. The large-scale climatic drivers such as sea surface temperature (SST) of equatorial Pacific and Indian Ocean as well as the El Niño-Southern Oscillation (ENSO) revealed no teleconnection with tree growth. The tree rings of this species are thus an indicator for monsoon precipitation variations in Bangladesh. The wider distribution of this species from the South to South East Asian coast presents an outstanding opportunity for developing a large-scale tree-ring network of mangroves.
Highlights
Mangroves are carbon rich ecosystems that lie at the interface between land and sea in the tropical and subtropical regions, providing a wide array of resources and services, such as protection against natural calamities, habitats for wildlife and fisheries, support socioeconomic activities and maintain ecological balance [1,2,3,4,5]
This study aims at exploring the dendroclimatological potential of H. fomes in the Sundarbans, and we address the following questions: i) do the ring-width series crossdate?, ii) which climatic factor mainly influences radial growth? and iii) do the large-scale climatic drivers, such as sea surface temperature (SST) in the equatorial Pacific and Indian Ocean and El Niño-Southern Oscillation (ENSO) influence local climate and/or tree growth?
Concentric tree rings are microscopically visible in all samples (Fig 3), and the tree-ring boundaries are marked by a marginal parenchyma band, predominantly one cell wide but occasionally up to three cells and occasionally mixed with fibers [38, 40]
Summary
Mangroves are carbon rich ecosystems that lie at the interface between land and sea in the tropical and subtropical regions, providing a wide array of resources and services, such as protection against natural calamities, habitats for wildlife and fisheries, support socioeconomic activities and maintain ecological balance [1,2,3,4,5]. The Bangladesh Sundarbans is one of the most diverse forests harboring more than 330 plant species, 400 species of fishes, 35 species of reptiles, over 300 species of birds, and 42 species of mammals including the Royal Bengal tiger [7, 8]. It has been declared a Ramsar site. The forest is increasingly threatened by excessive livelihood activities, land use changes [9], illegal and overexploitation of forest resources [10], diseases [11], biological invasion [12], natural calamities [13] and oil spills from vessels [14]. Climate change is another important threat to the ecosystem [15, 16]
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