Global trends in mangrove forest fragmentation

Abstract

fragmentation is a major driver of ecosystem degradation, reducing the capacity of habitats to provide many important ecosystem services. Mangrove ecosystem services, such as erosion prevention, shoreline protection and mitigation of climate change (through carbon sequestration), depend on the size and arrangement of forest patches, but we know little about broad-scale patterns of mangrove forest fragmentation. Here we conduct a multi-scale analysis using global estimates of mangrove density and regional drivers of mangrove deforestation to map relationships between habitat loss and fragmentation. Mangrove fragmentation was ubiquitous; however, there are geographic disparities between mangrove loss and fragmentation; some regions, like cambodia and the southern caribbean, had relatively little loss, but their forests have been extensively fragmented. in Southeast Asia, a global hotspot of mangrove loss, the conversion of forests to aquaculture and rice plantations were the biggest drivers of loss (>50%) and fragmentation. Surprisingly, conversion of forests to oil palm plantations, responsible for >15% of all deforestation in Southeast Asia, was only weakly correlated with mangrove fragmentation. Thus, the management of different deforestation drivers may increase or decrease fragmentation. Our findings suggest that large scale monitoring of mangrove forests should also consider fragmentation. this work highlights that regional priorities for conservation based on forest loss rates can overlook fragmentation and associated loss of ecosystem functionality.Mangroves are intertidal wetlands found along coastlines in much of the tropical, subtropical and warm-temperate world. These forests provide valuable ecosystem services including preventing erosion 1 , providing habitat for fisheries species 2 , protecting coastal communities from extreme weather events 3,4 and storing large reserves of blue carbon, thus mitigating global climate change 5 . The services provided by mangroves are threatened by anthropogenic processes including deforestation 6 and sea-level rise 7,8 . Historically, mangroves were subject to high rates of deforestation of up to 3.6% per annum 9 . However, since the turn of the millennium global mangrove deforestation rates have slowed, with annual loss rates of 0.2-0.7% 10,11 . Lower rates of loss are due to near total historical loss of forest patches in some regions, but also improved conservation practices 11 and improvements in large scale monitoring techniques that provide more accurate estimates of cover and loss than were available historically 10,12 . The majority of contemporary mangrove loss occurs in Southeast Asia, where ~50% of the remaining global mangrove forest area is located, with nations such as Indonesia, Malaysia and Myanmar continuing to show losses of 0.26, 0.41 and 0.70% per year, respectively 10 .Recently, researchers have highlighted that simply reporting mangrove total loss rates is insufficient for prioritising conservation actions 11 , if there is insufficient knowledge...

Global declines in human‐driven mangrove loss

“…Mangrove areas were therefore facing widespread clearing for aquaculture in particular far before our study period, suggesting that the CM hotspots and declines in CM loss recorded here could be reaching local ecological capacity. With the observed historic losses and continued fragmentation (Bryan‐Brown et al., 2020), the decline in human exploitation is therefore expected within CM hotspots. This has the potential to place pressure on local municipalities to forgo conservation policies and convert viable mangrove resources in protected areas, such as the Tanjung Panjang Nature Reserve in Sulawesi, Indonesia (Figure 3c,d).…”

“…For instance, the Southeast Asian Green Buffer policies(Friess et al 2016) prohibiting the conversion of mangroves within a certain distance from the ocean may temporarily preserve the value of mangroves as storm surge barriers, but as the shoreline retreats (e.g., ER), the buffering distance between ocean and aquaculture ponds will be reduced in the coming years. The emergence of extreme weather‐driven mangrove losses is expected to continue in the future irrespective of land‐use policy, as stressors such as extreme events and sea level rise cause large‐scale disturbances regardless of protection status (Bryan‐Brown et al 2020). Short‐term mangrove protection in regions immediately adjacent to eroding shorelines is necessary, but long‐term plans that account for coastal squeeze impacts as well as the effects of a changing climate are critical for maintaining mangrove ecosystem services.…”

“…Recent remote sensing‐based datasets documenting global mangrove deforestation have yielded annual loss rates of between 0.26 and 0.66 percent loss per year (Hamilton & Casey, 2016). These datasets have further been combined with field data to map higher‐level mangrove attributes at regional and global scales, including mangrove height (Simard et al., 2019), aboveground biomass/carbon (Simard et al., 2019; Tang et al., 2018) and soil carbon (Atwood et al., 2017; Jardine & Siikamäki, 2014; Rovai et al., 2018; Sanderman et al., 2018), and forest fragmentation (Bryan‐Brown et al., 2020). These studies highlight the important role of remote sensing in the monitoring of regional and global trends in mangrove ecosystem health and change.…”

Anthropogenic Drivers of Mangrove Loss and Associated Carbon Emissions in South Sumatra, Indonesia

“…Mangrove forests are found in intertidal regions along tropical and subtropical coastlines [1] between 30 • N and 30 • S latitude [2,3]. These forests grow along muddy beaches with a low hydrodynamic intensity, especially in areas with expansive river estuaries and deltas where sediments are continuously supplied by upland catchments.…”

La population d’Avicennia germinans du delta du Saloum est-elle relictuelle depuis la dernière période humide ?

“…Selon le dernier rapport de la FAO sur les mangroves, elles sont en effet passées de 18,8 millions d'hectares à 15,2 millions d'hectares de 1980de à 2005de (FAO, 2007. Des articles plus récents signalent néanmoins une amélioration (Bryan-Brown et al, 2020 ;Friess et al, 2020). Selon le rapport général de la FAO de 2020, la diminution des surfaces de mangrove a ralenti de moitié si l'on compare 1990-2000 et 2010-2020, de 47 000 ha par an à 21 000 ha par an.…”