1980s–2010s: The world's largest mangrove ecosystem is becoming homogeneous

Abstract

Knowledge gaps in spatiotemporal changes in mangrove diversity and composition have obstructed mangrove conservation programs across the tropics, but particularly in the Sundarbans (10,017 km 2 ), the world's largest remaining natural mangrove ecosystem. Using mangrove tree data collected from Earth's largest permanent sample plot network at four historical time points (1986, 1994, 1999 and 2014), this study establishes spatially explicit baseline biodiversity information for the Sundarbans. We determined the spatial and temporal differences in alpha, beta, and gamma diversity in three ecological zones (hypo-, meso-, and hypersaline) and also uncovered changes in the mangroves' overall geographic range and abundances therein. Spatially, the hyposaline mangrove communities were the most diverse and heterogeneous in species composition while the hypersaline communities were the least diverse and most homogeneous at all historical time points. Since 1986, we detect an increasing trend of compositional homogeneity (between-site similarity in species composition) and a significant spatial contraction of distinct and diverse areas over the entire ecosystem. Temporally, the western and southern hypersaline communities have undergone radical shifts in species composition due to population increase and range expansion of the native invasive species Ceriops decandra and local extinction or range contraction of specialists including the globally endangered Heritiera fomes . The surviving biodiversity hotspots are distributed outside the legislated protected area network. In addition to suggesting the immediate coverage of these hotspots under protected area management, our novel biodiversity insights and spatial maps can form the basis for spatial conservation planning, biodiversity monitoring and protection initiatives for the Sundarbans.

Can Strict Protection Stop the Decline of Mangrove Ecosystems in China? From Rapid Destruction to Rampant Degradation

“…The species assessed as CR, EN or VU are all distributed at the high or middle intertidal zones ( Table 2). Local extinction and range contraction of endangered mangrove species such as Heritiera fomes and abnormal expansion of native species such as Ceriops decandra have also been reported in Sundarbans [61]. These results also suggest what are being protected are not the diverse, healthy forests that used to occur.…”

“…Globally, most mangrove species are increasingly threatened and are undergoing contraction due to local extinction [59][60][61]. Although no mangrove species in China have been included on the list of globally threatened species [57] and there is no record of the extinction of mangrove species as yet (Table 2), the distribution ranges of some species and related wild resources have been drastically reduced.…”

Solving the fourth‐corner problem: forecasting ecosystem primary production from spatial multispecies trait‐based models

“…Moreover, biotic homogenization has been underway in the Sundarbans (Sarker et al. 2019 a ). The SLR rate along the Bangladesh coast in the 20th century (5.93 mm/yr) was substantially higher than the global average (1.0–2.0 mm/yr).…”

“…Finally, HH levels were determined from stump count records (measuring illegal harvesting between 1986 and 2014). See Sarker et al (2019a) for further details.…”

“…The detrimental effects of salinity intrusion and siltation on mangrove species distributions and diversity are well established (Sarker et al 2016(Sarker et al , 2019b. Moreover, biotic homogenization has been underway in the Sundarbans (Sarker et al 2019a). The SLR rate along the Bangladesh coast in the 20th century (5.93 mm/yr) was substantially higher than the global average (1.0-2.0 mm/yr).…”