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Assessment of Mangrove Carbon Stocks in Cameroon, Gabon, the Republic of Congo (RoC) and the Democratic Republic of Congo (DRC) Including their Potential for Reducing Emissions from Deforestation and Forest Degradation (REDD+)
Abstract
We present results of the field assessment using a total of fifteen 0.1 ha mangrove permanent sample plots (PSPs) in four selected countries in Central Africa, including: Cameroon, Gabon, Republic of Congo and Democratic of Republic, which together account for 90 % of mangroves in Central Africa. Above-and belowground carbon stocks were computed using data from the PSPs in all four countries. Long-term monitoring data in Cameroon were used to estimate carbon sequestration rates. Four major carbon pools were considered: aboveground carbon, belowground root carbon, deadwood and the soil organic carbon. All the eight mangrove species described in Central Africa were encountered in the study. The dominant species in Central Africa is Rhizophora racemosa, and it occupies more than 70 % of the forest formation. The average stand density ranged from a low of 450 tree/ha in degraded forest of RoC to a high of 3,256 tree/ha in undisturbed stands of Cameroon. Standing volume ranged from a low of 213 m 3 /ha in RoC to a high of 428 m 3 /ha in Cameroon; corresponding to aboveground biomass values of 251 and 505 Mg/ha, respectively. Together with the deadwoods, the total vegetation biomass in the study area ranged from a low of 394 Mg/ha in RoC to a high of 825 Mg/ha in Cameroon. Mean diameter increment for primary and secondary stems was 0.15 cm/year. This translates to above-and belowground annual biomass increments of 12.7 and 3.1 Mg/ha/year, respectively. Total ecosystem carbon in undisturbed system was estimated at 1520 ± 164 Mg/ha with 982 Mg/ ha (or 65 %) in belowground component (soils and roots) and 538 Mg/ha (35 %) in the aboveground components. Carbon density differed significantly (p \ 0.05) with forest
... The evaluation of carbon stock and storage potentials of mangrove soils is crucial to determining the amount of CO 2 released to the atmosphere which alters the equilibrium in carbon dioxide distribution amongst the reservoirs of the carbon cycle (Bindoff et al., 2019;Nwankwo et al., 2023). In Gabon, several studies on above and mangrove soil carbon stocks have already been conducted in Gabon (Ajonina et al., 2014;Trettin et al., 2021;Kauffman & Bhomia, 2017). However, uncertainties remain about spatial distribution of mangrove soils organic carbon stocks across country. ...
... Trettin et al. (2021) reported that SOC stocks in the top-meter soil in Pongara National Park in Gabon were 369 MgC ha −1 . Ajonina et al. (2014) reported SOC stocks of 345 MgC ha −1 in Akanda National Park, however, spatial variation of SOC stocks remain unclear. Soil organic carbon stocks may vary on a national scale, understanding the distribution mangrove soil organic carbon at nationwide is thus crucial to increase national carbon storage and will mitigate climate change (Jardine & Siikamäki, 2014;Sanderman et al., 2018;Bindoff et al., 2019). ...
... The study area as shown in Figure 1 is located along the coast of Gabon which is part of the Congo Basin. The climate is humid wet tropical with an average rainfall between 2400 on the eastern to 2830 mm on western side (Ajonina et al., 2014). At all sites, the main mangrove vegetation was Rhizophora racemosa L. (Kauffman & Bhomia, 2017. ...
Gabonese's estuary is an important coastal mangrove setting and soil plays a key role in mangrove carbon storage in mangrove forests. However, the spatial variation in soil organic carbon (SOC) storage remain unclear. To address this gap, determining the SOC spatial variation in Gabonese's estuarine is essential for better understanding the global carbon cycle. The present study compared soil organic carbon between northern and southern sites in different mangrove forest, Rhizophora racemosa and Avicennia germinans. The results showed that the mean SOC stocks at 1 m depth were 256.28 ± 127.29 MgC ha −1. Among the different regions, SOC in northern zone was significantly (p < 0.001) higher (232.45 ± 120.81 MgC ha −1) than that in the southern zone (143.19 ± 44 MgC ha −1). At all sites, SOC stocks were significantly higher in Rhizophora racemose (192.2 ± 114.17 MgC ha −1) than in Avicenia germinans (130.12 ± 161.16 MgC ha −1) (p < 0.001). The deeper layers contained higher SOC stocks (254.62 ± 128.09 MgC ha −1) than upper layers (55.42 ± 25.37 MgC ha −1). The study highlights that low deforestation rate have led to less CO 2 (705.3 Mg CO 2 e ha −1-922.62 Mg CO 2 e ha −1) emissions How to cite this paper: Obame 128 Open Journal of Forestry than most sediment carbon-rich mangroves in the world. These results highlight the influence of soil texture and mangrove forest types on the mangrove SOC stocks. The first national comparison of soil organic carbon stocks between mangroves and upland tropical forests indicated SOC stocks were two times more in mangroves soils (51.21 ± 45.00 MgC ha −1) than primary (20.33 ± 12.7 MgC ha −1), savanna and cropland (21.71 ± 15.10 MgC ha −1). We find that mangroves in this study emit lower dioxide-carbon equivalent emissions. This study highlights the importance of national inventories of soil organic carbon and can be used as a baseline on the role of mangroves in carbon se-questration and climate change mitigation but the variation in SOC stocks indicates the need for further national data.
... The evaluation of carbon stock and storage potentials of mangrove soils is crucial to determining the amount of CO 2 released to the atmosphere which alters the equilibrium in carbon dioxide distribution amongst the reservoirs of the carbon cycle (Bindoff et al., 2019;Nwankwo et al., 2023). In Gabon, several studies on above and mangrove soil carbon stocks have already been conducted in Gabon (Ajonina et al., 2014;Trettin et al., 2021;Kauffman & Bhomia, 2017). However, uncertainties remain about spatial distribution of mangrove soils organic carbon stocks across country. ...
... Trettin et al. (2021) reported that SOC stocks in the top-meter soil in Pongara National Park in Gabon were 369 MgC ha −1 . Ajonina et al. (2014) reported SOC stocks of 345 MgC ha −1 in Akanda National Park, however, spatial variation of SOC stocks remain unclear. Soil organic carbon stocks may vary on a national scale, understanding the distribution mangrove soil organic carbon at nationwide is thus crucial to increase national carbon storage and will mitigate climate change (Jardine & Siikamäki, 2014;Sanderman et al., 2018;Bindoff et al., 2019). ...
... The study area as shown in Figure 1 is located along the coast of Gabon which is part of the Congo Basin. The climate is humid wet tropical with an average rainfall between 2400 on the eastern to 2830 mm on western side (Ajonina et al., 2014). At all sites, the main mangrove vegetation was Rhizophora racemosa L. (Kauffman & Bhomia, 2017. ...
Gabonese's estuary is an important coastal mangrove setting and soil plays a key role in mangrove carbon storage in mangrove forests. However, the spatial variation in soil organic carbon (SOC) storage remain unclear. To address this gap, determining the SOC spatial variation in Gabonese's estuarine is essential for better understanding the global carbon cycle. The present study compared soil organic carbon between northern and southern sites in different mangrove forest, Rhizophora racemosa and Avicennia germinans. The results showed that the mean SOC stocks at 1 m depth were 256.28 ± 127.29 MgC ha −1. Among the different regions, SOC in northern zone was significantly (p < 0.001) higher (232.45 ± 120.81 MgC ha −1) than that in the southern zone (143.19 ± 44 MgC ha −1). At all sites, SOC stocks were significantly higher in Rhizophora racemose (192.2 ± 114.17 MgC ha −1) than in Avicenia germinans (130.12 ± 161.16 MgC ha −1) (p < 0.001). The deeper layers contained higher SOC stocks (254.62 ± 128.09 MgC ha −1) than upper layers (55.42 ± 25.37 MgC ha −1). The study highlights that low deforestation rate have led to less CO 2 (705.3 Mg CO 2 e ha −1-922.62 Mg CO 2 e ha −1) emissions How to cite this paper: Obame 128 Open Journal of Forestry than most sediment carbon-rich mangroves in the world. These results highlight the influence of soil texture and mangrove forest types on the mangrove SOC stocks. The first national comparison of soil organic carbon stocks between mangroves and upland tropical forests indicated SOC stocks were two times more in mangroves soils (51.21 ± 45.00 MgC ha −1) than primary (20.33 ± 12.7 MgC ha −1), savanna and cropland (21.71 ± 15.10 MgC ha −1). We find that mangroves in this study emit lower dioxide-carbon equivalent emissions. This study highlights the importance of national inventories of soil organic carbon and can be used as a baseline on the role of mangroves in carbon se-questration and climate change mitigation but the variation in SOC stocks indicates the need for further national data.
... Some studies in Africa have already addressed certain effects of human-driven mangrove degradation. For instance, Ajonina et al. (2014a) studied mangroves in Cameroon, Gabon, the Republic of Congo (RoC), and the Democratic Republic of Congo (DRC). These authors showed that all carbon pools (aboveground (AGC), belowground (BGC), soil organic carbon (SOC)) decreased with increasing human-driven degradation pressures. ...
... These authors showed that all carbon pools (aboveground (AGC), belowground (BGC), soil organic carbon (SOC)) decreased with increasing human-driven degradation pressures. While AGC decreased by 74-88 %, SOC decreased by 20-23 % (Ajonina et al., 2014a). However, Ajonina et al. (2014a) did not investigate effects on species composition. ...
... While AGC decreased by 74-88 %, SOC decreased by 20-23 % (Ajonina et al., 2014a). However, Ajonina et al. (2014a) did not investigate effects on species composition. Indeed, very few studies considered the effect of degradation on species composition. ...
... In Central Africa, Ajonina et al. (2014b) implemented a general biomass prediction model with a DBH range of 1 to 102.8 cm. However, no equations are specific to neither mangrove species nor tree components (bark, wood) in Gabon. ...
... All of our allometric equations for tree components (bark or wood) have lower RMSEs than Ajonina's general model for the mangroves of Benin. More geographically close, the model from Cameroon has a similar margin of error as the general mixed model (0.016 average errors and a 0.256% bias) (Ajonina et al., 2014b). This similarity is not the case for other models. ...
... The results prove to be satisfactory as the predictive specific and general allometric equations show low RMSE and biases under 1%. Their accuracy is similar to the local models of Benin and Cameroon (Ajonina et al., 2014a;2014b). This is not the case when comparing to allometric equations developed in other regions, such as French Guiana and Southeast Asia. ...
The aboveground biomass (AGB) of Gabonese mangroves is commonly estimated from equations calibrated in other countries, and is generally adapted poorly to the local context. This paper focuses on developing local allometric equations for the AGB estimation and to evaluate their accuracy compared to other general equations. The local equations for Rhizophora spp and Avicennia germinans were performed with tree volume, bark and wood densities, and are used with the diameter as an independent variable. The heights and diameters of 408 trees (314 Rhizophora spp and 94 Avicennia germinans) were measured at 13 sites in Estuaire Province. Sixty four aliquots were taken from the trunks of both species at the Mondah site. This site has tree diameters ranging from 2 to 127 cm for Avicennia and from 1.4 to 75.8 cm for Rhizophora. The tree height ranges from 0.9 to 24 m for Avicennia, and from 1.1 to 53 m for Rhizophora. Avicennia has an overall trunk density of 0.88 g/cm3 and Rhizophora has 1.17 g/cm3. The coefficient of determination (R2) of the equations are 0.98 for Rhizophora spp, 0.97 for Avicennia germinans, and 0.99 for the general equation. The seven equation display biases that are less than 1% and the root mean square errors vary between 0.073 and 1.68. Compared to other equations generally used, these local equations improve the accuracy of aboveground biomass estimations of Gabonese mangroves.
... Mangrove forests provides various services such as source of fuel and medicine (Alongi, 2002), fishery products (Sukardjo, 1994), shoreline protection (Ajonina et al., 2014), supports coastal nutrient cycling in the coastal zone (Alongi et al., 2000), and carbon sink and source in the plant body and in the soils below (Kathiresan, Gomathi, Anburaj & Saravanakumar, 2014). In fact, mangroves are considered one of the most carbon-rich ecosystems in the world (He et al., 2018;Donato et al., 2011), despite occupying only 0.5% of the global coastal area (Tinh et al., 2020;He et al., 2018). ...
... However, estimates of carbon stored belowground, such as the tree roots and soils of terrestrial and mangrove forests were limited (Komiyama et al., 2005;Ajonina et al., 2014). Information has narrowed even more when it comes to the ability of mangroves to sequester carbon (Ajonina et al., 2014). ...
... However, estimates of carbon stored belowground, such as the tree roots and soils of terrestrial and mangrove forests were limited (Komiyama et al., 2005;Ajonina et al., 2014). Information has narrowed even more when it comes to the ability of mangroves to sequester carbon (Ajonina et al., 2014). ...
In mangrove forests, soils were considered as the largest carbon pool. The result of the study conducted in Barangay San Roque, Socorro, Surigao del Norte showed that the mean soil carbon stock of the top 100cm soil layer of the estimated 50-hectare mangrove forest is 489.3C Mg ha-1. This was attributed by the forest's stand age, species composition, and the absence of direct anthropogenic activities that can influence the primary production. Increases in soil carbon stock were observed as depth increases. However, analysis showed no statistical significance between bulk density and organic carbon concentration at different depths, as well as between soil carbon stock at the different forest parts. Nonetheless, the mean soil carbon stock of the mangrove forest in the study is higher than those in the terrestrial forest. With these, the mangrove stands in Socorro, Surigao del Norte can be considered an important carbon reserve in the province and should be protected from degradation and land-use conversion to manage the potential carbon emission from this pool.
... Mangrove forests provides various services such as source of fuel and medicine (Alongi, 2002), fishery products (Sukardjo, 1994), shoreline protection (Ajonina et al., 2014), supports coastal nutrient cycling in the coastal zone (Alongi et al., 2000), and carbon sink and source in the plant body and in the soils below (Kathiresan, Gomathi, Anburaj & Saravanakumar, 2014). In fact, mangroves are considered one of the most carbon-rich ecosystems in the world (He et al., 2018;Donato et al., 2011), despite occupying only 0.5% of the global coastal area (Tinh et al., 2020;He et al., 2018). ...
... However, estimates of carbon stored belowground, such as the tree roots and soils of terrestrial and mangrove forests were limited (Komiyama et al., 2005;Ajonina et al., 2014). Information has narrowed even more when it comes to the ability of mangroves to sequester carbon (Ajonina et al., 2014). ...
... However, estimates of carbon stored belowground, such as the tree roots and soils of terrestrial and mangrove forests were limited (Komiyama et al., 2005;Ajonina et al., 2014). Information has narrowed even more when it comes to the ability of mangroves to sequester carbon (Ajonina et al., 2014). ...
The research is on the quantification of soil carbon in the soils of the primary mangrove forests of Socorro, Surigao del Norte.
... Mangrove ecosystems provide a range of goods, services and support high levels of biodiversity (Duarte et al., 2005). A growing body of literature suggests that mangroves are highly potential in sequestering significant amounts of CO 2 (Donato et al., 2011;Ajonina et al., 2014;Jones et al., 2015;Stringer et al., 2015;Trettin et al., 2016Trettin et al., , 2021. Despite their small cover of about 0.81% of the global tropical forests (Bunting et al., 2018;FAO and UNEP, 2020;Spalding and Leal, 2021), mangroves represent a globally important carbon sink (Donato et al., 2011;Sanderman et al., 2018). ...
... Other studies reported values different from values obtained by this study. Alemayehu et al. (2014) reported the ABG C was 148.07 Mg C ha − 1 for mangroves in Mida Creek and Ajonina et al. (2014) reported 537.7 Mg C ha − 1 in undisturbed mangroves of central African countries. Above ground biomass carbon reported by this study in the degraded plots (0-150.73 ...
... Mg C ha − 1 ) differs from values reported by other studies in disturbed mangroves. For instance, Ajonina et al. (2014) reported 64.1 Mg C ha − 1 in heavily exploited mangroves in central African countries. The highest AGC stock was recorded in plot 13 which had larger trees of B. racemosa. ...
Mangrove forests provide important ecosystem services to the human society and nature including mitigation of climate change. The quality and quantity of ecosystem services offered by mangrove forests are however at risk when mangroves are degraded. The restoration of mangrove areas is considered as a natural solution to recover lost ecosystem services such as securing of carbon stocks. This study was set to assess the extent to which mangrove planting activities compensate for the loss of biomass carbon stocks and other structural attributes in Rufiji Delta-Tanzania through analysis of biomass carbon loss and gain as a result of conversion of mangroves forest into rice farms and planting of mangroves respectively. Circular sampling plots were established in good, degraded and restored mangrove areas where total tree heights and Diameter at Breast Height (DBH) of all standing trees were measured and recorded by species and used to compute biomass carbon stock. The mangrove species composition changed from 7 in 1989 to 2 species in degraded plots in 2016. The species dominance changed from Avicennia marina in 1989 to Rhizophora mucronata in 2016 in good mangrove plots and from A. marina and Sonneratia alba to an invasive Baringtonia racemosa in degraded plots. Bruguiera gymnorrhiza was the only mangrove species used for restoration through planting in the delta and the overall survival rate was 37%. The above-ground carbon (AGC) and below-ground carbon (BGC) for the good natural mangrove plots ranged from 28.18 – 299.43 and 16.00 – 164.51 Mg C ha⁻¹ respectively compared to 0 –150.88 and 0 – 967.01 Mg C ha⁻¹ in the degraded plots. The total biomass carbon stock in the good natural mangrove plots ranged from 44.14 – 463.94 Mg C ha⁻¹ while for the degraded plots the range was 0 – 247.89 Mg C ha⁻¹. The carbon stocks in 5, 10 and 15 year old planted mangroves were 13.65, 20.13 and 57.53 Mg C ha⁻¹ respectively. The biomass loss of 172.91 Mg C ha⁻¹ was estimated in a period of 25 years (1989-2016), equivalent to an annual loss rate of 6.9 Mg C ha⁻¹year⁻¹, demonstrating that degradation has a significant contribution to loss of carbon stocks. Nevertheless, an average of 3.8 Mg C ha⁻¹year⁻¹ was stocked by 15 years old planted mangroves, demonstrating that there is potential for the planted mangroves to compensate for the lost carbon if the anthropogenic drivers such as rice farming is controlled. These findings call for urgent collective actions among stakeholders to consider and improve the integrated management of the delta.
... In Central Africa, Ajonina et al. (2014b) implemented a general biomass prediction model with a DBH range of 1 to 102.8 cm. However, no equations are specific to neither mangrove species nor tree components (bark, wood) in Gabon. ...
... All of our allometric equations for tree components (bark or wood) have lower RMSEs than Ajonina's general model for the mangroves of Benin. More geographically close, the model from Cameroon has a similar margin of error as the general mixed model (0.016 average errors and a 0.256% bias) (Ajonina et al., 2014b). This similarity is not the case for other models. ...
... The results prove to be satisfactory as the predictive specific and general allometric equations show low RMSE and biases under 1%. Their accuracy is similar to the local models of Benin and Cameroon (Ajonina et al., 2014a;2014b). This is not the case when comparing to allometric equations developed in other regions, such as French Guiana and Southeast Asia. ...
The aboveground biomass (AGB) of Gabonese mangroves is commonly estimated from equations calibrated in other countries, and is generally adapted poorly to the local context. This paper focuses on developing local allometric equations for the AGB estimation and to evaluate their accuracy compared to other general equations. The local equations for Rhizophora spp and Avicennia germinans were performed with tree volume, bark and wood densities, and are used with the diameter as an independent variable. The heights and diameters of 408 trees (314 Rhizophora spp and 94 Avicennia germinans) were measured at 13 sites in Estuaire Province. Sixty-four aliquots were taken from the trunks of both species at the Mondah site. This site has tree diameters ranging from 2 to 127 cm for Avicennia and from 1.4 to 75.8 cm for Rhizophora. The tree height ranges from 0.9 to 24 m for Avicennia, and from 1.1 to 53 m for Rhizophora. Avicennia has an overall trunk density of 0.88 g/cm3 and Rhizophora has 1.17 g/cm3. The coefficient of determination (R2) of the equations are 0.98 for Rhizophora spp, 0.97 for Avicennia germinans, and 0.99 for the general equation. The seven equation display biases that are less than 1% and the root mean square errors vary between 0.073 and 1.68. Compared to other equations generally used, these local equations improve the accuracy of aboveground biomass estimations of Gabonese mangroves.
... Estimées à une superficie totale de 2500 km² (Lebigre, 1990), les mangroves gabonaises constituent environ 12,41 % des mangroves d'Afrique centrale. Elles sont composées de neuf espèces de plante avec six (6) espèces de mangroves pures (Tomlinson, 1986) ou strictes (FAO, 2005), parmi lesquelles trois du genre Rhizophora (mangle, harrisonii et racemosa) (Ondo Assoumou, 2006 ;Ajonina et al., 2014a), puis Avicennia germinans (Avicenniaceae), Laguncularia racemosa et Conocarpus erectus (Combretaceae). A ces dernières s'ajoutent les espèces dites accompagnatrices et occasionnelles, Phoenix reclinata (Palmaceae) assez répandue dans les écosystèmes mangroves du Gabon, la fougère dorée Acrostichum aureaum (Pteridaceae), la graminée Paspalum vaginatum et les Pandanus (Pandanaceae) (Ondo Assoumou, 2017). ...
... A ces dernières s'ajoutent les espèces dites accompagnatrices et occasionnelles, Phoenix reclinata (Palmaceae) assez répandue dans les écosystèmes mangroves du Gabon, la fougère dorée Acrostichum aureaum (Pteridaceae), la graminée Paspalum vaginatum et les Pandanus (Pandanaceae) (Ondo Assoumou, 2017). Les travaux antérieurs réalisés sur les mangroves du Gabon (Lebigre, 1983(Lebigre, et 1990Ondo Assoumou, 2006Ajonina et al., 2014a) montrent que les Rhizophora sont les mieux représentés en termes de diversité spécifique et de couverture spatiale. Ils s'implantent aussi bien en zone frontale qu'au contact avec la terre ferme, et participent considérablement au stockage de la biomasse et du carbone. ...
... Les mangroves échantillonnées présentent des caractéristiques structurales assez communes avec des hauteurs variant de 1 à 18m, qualifiées de petites à moyennes par Lebigre (1983Lebigre ( , 1990. Replacés dans le contexte national, les Rhizophora spp n'atteignent pas les hauteurs maximales enregistrées au Gabon par Ajonina et al. (2014a) (Lebigre, 1990 ;Ondo Assoumou, 2006). ...
L’évaluation du stock de carbone des écosystèmes est une des principales recommandations de la Convention-cadre des Nations Unies
sur les Changements Climatiques en 1994. Le choix d’une méthode fiable, sans biais d’estimation, est une préoccupation des études
scientifiques. Les équations allométriques représentent une méthode précise de quantitification du carbone. Cependant, elles peuvent
varier suivant les espèces et/ou les écosystèmes. Cette étude a évalué la précison d’estimation du carbone de deux équations allométriques,
pour trois espèces du genre Rhizophora des mangroves des rivières Lowé et Igoumié dans la commune d’Owendo, au Sud de Libreville
(Gabon). Une collecte de données (diamètre à hauteur de poitrine et hauteur à la cime) a été effectuée sur 2020 m² de mangroves. La
régression, sur les variables biomasse aérienne (AGB) et diamètre à hauteur de poitrine (DBH), a permis de tester deux modèles : l’un
linéaire (AGB = 0,017*DBH-0,083+0,045), et l’autre, non-linéaire (AGB = 0,0001073*DBH2,71). Sur la base des valeurs du coefficient de
détermination, du critère d’information d’Akaïke (AIC) et de l’homoscédasticité des résidus, le modèle non linéaire est plus adéquat pour
une bonne estimation de la biomasse aérienne des espèces du genre Rhizophora des mangroves étudiées. L’erreur quadratique moyenne
(RMSE) est de 0,0014 et le biais est de -0,35%. Les mangroves échantillonnées ont une biomasse aérienne de 57,6416 Mg ha-1. Cela
équivaut à un stock de carbone aérien de 28,821 Mg C ha-1, et représente un taux d’émision atmosphérique de 105,772 Mg CO2 ha-1.
... Africa hosts about 19% of the world's mangroves, yet there are relatively few studies that have examined the carbon stocks of African mangroves (24), and the studies available report great differences among sites and amongst the different pools of carbon stocks, particularly between the above ground carbon (AGC) stored in the trees and the organic carbon sored within the sediment -'soil organic carbon (SOC)'. For example, SOC estimates for 1m depth range from 122 Mg C ha -1 in Republic of Congo (25) to 342 Mg C ha -1 in Liberia (24). In a single estuary in Liberia, total ecosystem carbon stocks (AGC+ SOC) varied by over fourfold, ranging from 366 to 1,485 ...
... The AGC values reported in this study are similar to other Tanzanian studies but lower than for example in the Democratic Republic of Congo (25). This could be attributed to the combination of: i) different methods used to sample AGC (Table 2), ii) different environmental characteristics (e.g. ...
... Beyond the zone of soil erosion, plots closest to the shore, which experience greater tidal inundation (and salinity), have slower decomposition rates, and therefore, higher SOC stocks. Mangrove's sediments can store high amounts of carbon due to complex root structures, high sedimentation rates and waterlogged conditions which impedes microbial degradation and slows decay [16,25]. ...
Background: Mangrove forests have gained recognition for their potential role in climate change mitigation due to the carbon sequestration of the productive ecosystems and storage in the sediments that are trapped by the mangrove tree roots and pneumatophores. Africa hosts about 19% of the world’s mangroves, yet there are relatively few studies that have examined the carbon stocks of African mangroves, and the studies available report great differences among sites and amongst the different pools of carbon stocks, particularly between the above ground carbon stored in trees (AGC) and organic carbon stored within the sediment - ‘soil organic carbon (SOC)’ and none considered the effects of seaward distance. We investigate if AGC and SOC carbon stocks differ with increasing seaward distance for estuarine mangroves in Tanzania and, how our results compare to those reported elsewhere across Africa.
Results: AGC ranged between 10.9-54.9 Mg C ha-1 , but was not significantly affected by seaward distance. SOC for 0-1m depth ranged from 153.7-483.6, with a mean of 301.7 Mg C ha⁻¹. SOC was significantly negatively correlated with seaward distance, which is different from studies in Micronesia and the Indo-Pacific. Mangrove type (estuarine/oceanic), soil erosion and soil depth may explain these differences We note important methodological differences in previous studies on carbon stocks in mangroves in Africa.
Conclusion:
This study indicates that seaward distance has an important effect on SOC stocks in the Lindi region of Tanzania. There is the need to standardise methodological approaches for mangroves in Africa, to report seaward distance and to describe the type of mangrove stand to make results easily comparable across sites and to assess the true value of Blue Carbon in Africa. We recommend focusing on trees >10cm diameter for AGC, and sampling soils to greater than 1m depth for SOC, which would provide a more complete assessment of the potentially considerable mangrove carbon store.
... Mangrove forests in Benin are characterized by plant species such as Rhizophora racemosa G. Mey, Avicennia germinans (L.) L., Laguncularia racemosa (L.) L.C. Gaertn. and Conocarpus erectus L. Previous studies have noted the limited species diversity of mangroves in West Africa, which are often dominated by two or three true mangrove species [57]. These mangrove forests also host important fauna such as Jacana actophilornis, Hippopotamus amphibious, Trichechus senegalensis, Lepidochelys olivacea, Dermochelys coriacea, Cercopithecus erythrogaster, Tragelaphus spekei, etc. [57]. ...
... and Conocarpus erectus L. Previous studies have noted the limited species diversity of mangroves in West Africa, which are often dominated by two or three true mangrove species [57]. These mangrove forests also host important fauna such as Jacana actophilornis, Hippopotamus amphibious, Trichechus senegalensis, Lepidochelys olivacea, Dermochelys coriacea, Cercopithecus erythrogaster, Tragelaphus spekei, etc. [57]. ...
Accurate estimation of biomass and carbon stocks in mangrove forests is a prerequisite for a better understanding of their role in climate regulation. Allometric equations remain appropriate tools in this context but are lacking for many mangrove species and sites across Africa. In this study, we destructively sampled 68 individual trees of the two dominant West African mangrove species (Rhizophora racemosa and Avicennia germinans) to (i) determine species-specific height-diameter allometry; (ii) evaluate biomass allocation to stem, branches, leaves and roots components; (iii) establish species-specific aboveground-, belowground- and total biomass allometric equations; and (iv) examine the accuracy of our best biomass model against existing equations for mangroves. Diameter at breast height (Dbh), total height (H), wood density and crown diameter were used as predictors in the models.
Results showed that Dbh explained 53% and 62% of height variation for R. racemosa and A. germinans, respectively. Stems stored the highest biomass fractions (84.30% for R. racemosa and 52.80% for A. germinans), followed by branches, while the belowground compartment contributed to 19%–22% of the total biomass. Among the candidate biomass models, the models incorporating Dbh and height as a compound variable (Dbh2H) were the most suitable for estimating aboveground and total biomass, with 87–92% of explained variance. For the root components, wood density and crown diameter were additionally found to improve model performance for R. racemosa and A. germinans, respectively. Our study revealed that biomass in West African mangrove forests was more accurately predicted using the established equations than with the existing models.
... Mangrove forests in Benin are characterized by plant species such as Rhizophora racemosa G. Mey, Avicennia germinans (L.) L., Laguncularia racemosa (L.) L.C. Gaertn. and Conocarpus erectus L. Previous studies have noted the limited species diversity of mangroves in West Africa, which are often dominated by two or three true mangrove species [57]. These mangrove forests also host important fauna such as Jacana actophilornis, Hippopotamus amphibious, Trichechus senegalensis, Lepidochelys olivacea, Dermochelys coriacea, Cercopithecus erythrogaster, Tragelaphus spekei, etc. [57]. ...
... and Conocarpus erectus L. Previous studies have noted the limited species diversity of mangroves in West Africa, which are often dominated by two or three true mangrove species [57]. These mangrove forests also host important fauna such as Jacana actophilornis, Hippopotamus amphibious, Trichechus senegalensis, Lepidochelys olivacea, Dermochelys coriacea, Cercopithecus erythrogaster, Tragelaphus spekei, etc. [57]. ...
... The maximum likelihood algorithm was used for the classification of these images and to produce maps of class distributions. The maximum likelihood method is widely used [26,41,[47][48][49] because of its ability to classify pixels on a probabilistic basis by highlighting the standard margin of error between pixel values and those of different areas of interest [50]. Preclassification operations making radiometric and geometric corrections using ENVI software served to improve the quality of the images before processing. ...
... The maximum likelihood algorithm was used for the classification of these images and to produce maps of class distributions. The maximum likelihood method is widely used [26,41,[47][48][49] because of its ability to classify pixels on a probabilistic basis by highlighting the standard margin of error between pixel values and those of different areas of interest [50]. ...
Land and resource use patterns in coastal areas play a key role in the resilience of ecosystems and populations to climate change. Knowing their spatiotemporal dynamics therefore constitutes a strategic tool to help decision-makers. Based on documentary research, geographic information system (GIS), image processing, and field work, this article maps land use on Manoka Island between 1986 and 2018 and identifies the drivers of change and avenues for intervention with a view to strengthening climate change mitigation. The results show a decrease of 4% in forest area on Manoka Island, representing an average of 112 ha of inland forest and 267 ha of mangrove converted between 1986 and 2018. This increases the degraded forest area by 268% (degraded mangrove and degraded inland forest) and exposes some camps to erosion and flooding. Reduction in forest area is mainly linked to the harvesting of fuelwood and the conversion of forests into farmland and residential areas. Settlements have increased in area from 15 ha in 1986 to 90.4 ha in 2018 to the detriment of natural spaces.
... Blue carbon assessments have already been carried out on the African continent. However, C storage research in Africa has largely stemmed from the inclusion of African mangroves in the UN Reducing Emissions from Deforestation and Forest Degradation (REDDþ) program (Ajonina et al., 2014;Ahmed and Glaser, 2016). Approximately 19% of global mangrove coverage is located in Africa (Ajonina, 2008;Giri et al., 2011). ...
... Approximately 19% of global mangrove coverage is located in Africa (Ajonina, 2008;Giri et al., 2011). Large mangrove forests in tropical and subtropical areas of Africa have therefore been the primary focus of C storage assessments in central (Republic of the Congo and DR Congo), east (Tanzania and Kenya), west (Nigeria and Cameroon), and southern (Mozambique) African regions (Ajonina et al., 2014;Sitoe et al., 2014;Stringer et al., 2015;Tang et al., 2016;Njana et al., 2017). However, African mangroves also extend beyond the subtropical biogeographic boundary into warm-temperate regions along the coast of South Africa. ...
Carbon (C) storage by vegetated coastal habitats (mangroves, salt marshes and seagrasses) is globally recognized as a critical ecosystem service. Research efforts have therefore focused on quantifying C stored in these “blue carbon” ecosystems but a notable knowledge gap still exists for certain geographical regions. This study aimed to provide the first comprehensive assessment of C storage in South African warm temperate mangroves by quantifying the C storage in aboveground biomass and soil C pools associated with the mangrove forest at the Nxaxo Estuary. C storage variability was also related to mangrove forest structure and soil environmental variables. C storage was quantified using standardized protocols for aboveground (live trees, leaf litter, pneumatophores) and soil C pools at five Avicennia marina sites. The results showed soil C storage to be spatially variable while aboveground C pools were similar between intertidal zones within the sites. The soil C pool made the largest contribution to total C storage at each site and ranged from 176.91 ± 4.5MgC.ha⁻¹ to 262.53 ± 18.8 MgC.ha⁻¹. Of the aboveground carbon pools, live trees made the largest contribution and ranged from 2.25 ± 1.0 MgC.ha⁻¹ to 9.56 ± 3.6 MgC.ha⁻¹. Across all sites, average C storage for all pools was 234.9 ± 39.16 MgC.ha⁻¹, which falls within the range reported for mangroves at other southern hemisphere range limits. Variability in soil C was linearly related to soil organic matter but this relationship was inconsistent between different soil depth intervals that were sampled. Total C storage was inversely related to mangrove tree density. This study confirms the need for more blue carbon studies to quantify C storage in under-represented geographical areas and to investigate factors that drive variability in C storage at different spatial scales.
... Wood contributes to sustainably limit global warming by fixing greenhouse gases [1]. In Central Africa and more specifically in equatorial regions, the forest plays a key role in this regulation [2,3]. In the case of Gabon, which shelters various species [4], the forest represents 85% of the territory, among which 13% represents protected national parks. ...
... Theoretical and Applied Fracture Mechanics 95 (2018) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] appearance, making the phenomenon unstable. An apparent crack stability is observed if the thickness of the CTS specimen becomes significant. ...
The cracking properties in opening mode of three tropicals species from the Gabonese forest, namely Iroko (Milicia Excelsa), Okume (Aucoumea klaineana Pierre), and Padouk (Pterocarpus soyauxii), were investigated in this study. Various tests were performed at room temperature and for two different thicknesses. A full-field measurement technique, namely the grid method, was used in order to obtain the displacement and strain maps near the crack during the tests. The mechanical parameters, the specificities of the wood species, the Arcan system and the grid transfer method are first described. For all the specimens, the initial crack length was oriented along the fiber direction (RL). The instantaneous failure tests were performed using two types of specimens: the modified Compact Tension Shear (CTS) and the Mixed Mode Crack Growth (MMCG) specimens. The images of the grid were recorded and analyzed to obtain the displacement maps. The crack opening, the location of the crack tip as well as the strain fields on the surface of the specimens were deduced from these displacement maps. The experimental critical energy release rate Gc was evaluated by the compliance method in imposed displacement. In the case of instantaneous crack with CTS specimens, the comparison of the initial value of Gc for all the samples show that this quantity strongly depends on the thickness and density of the species under study. Crack propagation was observed for a thickness equal to 20 mm only. The results of the crack propagation with the MMCG specimens show the same dependence, and confirm the quasi-brittle fracture behavior of Iroko. The experimental results are scattered, but clear trends can be observed concerning the fracture parameters of the in previous studies described in the literature on wood species with wood species under study. The results are finally compared with those given densities similar to those studied here.
... The national forestry potential of Cameroon is estimated at about 1.5 billion of m 3 with about hundred wood species. Nowadays, about 20%-30% of wood species are exploited and used mostly for external commercialization rather than constructions in the country (Ajonina et al. 2014). The biological nature of wood gives the advantage of being renewable and attention should be paid to wood as a building material (Mvondo et al. 2017). ...
This work uses the M-theta method on a new proposed specimen called "I-specimen" for the numerical modeling of cracks on some tropical hardwoods in general and in particular on some Cameroonian woods. The finite element analysis of fracture in an orthotropic medium is developed. The fracture algorithm is introduced in a finite element software Cast3M and, with an incremental orthotropic formulation, the simulation of crack growth is computed. Using this method, stress intensity factors and energy release rate are calculated for Mode I and II failures. The energy release rate and stress intensity factors are numerically deduced using “I-specimen” to characterize three Cameroonian hardwoods under mode I and II loading for different crack growths. The specimen used has better characteristics than other samples generally used in the literature and its geometry is very simple to define. The proposal of a new geometry that can guarantee the reproduction of the different failure modes while exhibiting some stability of the crack parameters G and K during propagation was evaluated and compared to other specimens given by the fracture mechanics literature. For each fracture mode, the influence of the orthotropy rate parameters on the energy release rate was investigated.
... Since the establishment of the UNFCCC, a variety of market mechanisms and policy instruments have evolved to facilitate mitigation of GHG emissions, adaptation to impacts of global warming, and positive sustainable development outcomes. These include the Clean Development Mechanism (CDM) (O'Sullivan et al., 2012), emissions trading schemes (Siikamäki et al., 2012), and the Reducing Emissions from Deforestation and Forest Degradation (REDD+) concept (Ajonina et al., 2014). All of these different schemes and initiatives share a common feature: they determine market outcomes using carbonor more specifically, tonnes of carbon dioxide equivalent (tCO 2 e) -as a standard metric (Adame et al., 2013). ...
... Existing scientific information on the part of the reserve in Benin covers aspects pertaining to the local use of mangroves in Grand-Popo, one of the municipalities embedded in the reserve in Benin [11]. It also covers the characterization of the provisioning services delivered by mangroves in some localities of the reserve [12][13][14] and the carbon storage capacity of mangroves [15]. In the Togolese part of the reserve, no scientific record exists on mangrove ES to our knowledge. ...
Mangroves are important coastal ecosystems, which deliver diverse and crucial services to humans. This study explored the diversity of mangrove ecosystem services, their associated threats as well as their contribution to livelihoods and wellbeing of coastal communities in the Mono Transboundary Biosphere Reserve (MTBR) located between Benin and Togo. Data were collected using the exploratory sequential mixed method. The approach included field reconnaissance, focus group discussions (n = 14), in-depth interviews (n = 17), household survey (n = 274) and direct observations. A total of 21 services and 7 associated threats were recorded in the entire reserve. Provisioning services were the most important service for mangroves in the reserve followed by supporting services, regulating services and cultural services. Change in water salinity, mangrove overharvesting and illegal, unreported and unregulated fishing were the three major threats to mangrove ecosystem services in the reserve. Most of the respondents indicated that the current flow of provisioning services, regulating services and cultural services does not sustain their wellbeing and livelihoods. However, the perception varied significantly across respondents’ gender, ethnical groups, educational background and country. Our study showed some similarities between the two countries but also highlighted important differences which can assist the sustainable management of mangroves in the MTBR.
... The average SOC in mangroves of Lamu (mean ± 95% C.I: 393.48 ± 98.58 Mg C ha −1 ), is within the global range of 37.0 -2,102.7 Mg C ha −1 (Alongi, 2020); and is comparable to similar studies in the mangroves of Madagascar, 381.02 Mg C ha −1 (Benson et al., 2017), Gabon, 392 Mg C ha −1 (Ajonina et al., 2014) and Brazil, 341 Mg C ha −1 (Kauffman et al., 2018). Soil storage potential of mangroves in Lamu was, however, lower than the global average of 749 Mg C ha −1 (Alongi, 2020) as well as the Indo-Pacific region, 864 Mg C ha −1 , and Indonesia, 879 Mg C ha −1 (Murdiyarso et al., 2015) mangroves. ...
Mangroves are carbon-rich ecosystems found in tropical and subtropical areas around the world. However, they are threatened by a combination of natural and human-induced factors. When mangroves are lost or degraded, their co-benefits to human society are greatly diminished along with the ecosystem’s ability to sequester carbon. The current study assessed mangrove cover and cover change, as well as measuring carbon stocks and their emissions levels from the mangroves of Lamu County, Kenya. We sampled above-and below-ground carbon pools, including soil organic carbon (SOC), in 191 plots distributed throughout the study area. Lastly, we evaluated the economics of avoiding mangrove deforestation based on the carbon-offset market. The total carbon stock of mangroves in Lamu was estimated at 20 million Mg C, with an average density of 560.22 ± 79.79 Mg C ha–1. Southern swamps recorded significantly higher carbon densities (p < 0.05) than other mangrove management blocks in Lamu. At least 1,739 ha of mangroves in Lamu were lost between 1990 and 2019 due to anthropogenic activities, representing a decline of 60 ha yr–1. Total emissions from loss and degradation of mangroves in Lamu is estimated at 140.1 Mg C ha–1; which translates to 30,840.1 Mg CO2e yr–1. Assuming an offset price of US308,401 yr–1 plus other co-benefits such as fishery functions and shoreline protection. Mainstreaming mangroves and associated blue carbon ecosystems into national development and climate change agenda could accelerate Kenya’s achievements of both Sustainable Development Goals (SDGs) and the Paris Agreement.
... Since the establishment of the UNFCCC, a variety of market mechanisms and policy instruments have evolved to facilitate mitigation of GHG emissions, adaptation to impacts of global warming, and positive sustainable development outcomes. These include the Clean Development Mechanism (CDM) (O'Sullivan et al., 2012), emissions trading schemes (Siikamäki et al., 2012), and the Reducing Emissions from Deforestation and Forest Degradation (REDD+) concept (Ajonina et al., 2014). All of these different schemes and initiatives share a common feature: they determine market outcomes using carbonor more specifically, tonnes of carbon dioxide equivalent (tCO 2 e) -as a standard metric (Adame et al., 2013). ...
Mangrove forests play a crucial role in the carbon cycle and mitigate climate change by reducing carbon dioxide emissions. However, mangrove ecosystems have declined dramatically in most regions due to natural and human factors, resulting in the release of substantial amounts of carbon dioxide. ‘Blue carbon’ conservation and restoration initiatives seek to reduce greenhouse gas emissions and support adaptation in mangrove areas. Various methods are employed to estimate, map, and monitor the extent and dynamics of mangrove biomass and carbon stocks, and these play a critical role in sustainable management and the climate policy and market instruments which can provide financial support for ecosystem conservation and restoration. This paper presents a comprehensive review of different mapping and monitoring methods applied from 2010 to 2020 for carbon stocks in mangrove forests, and highlights the limitations of previous studies. Destructive sampling, use of allometric equations, and remote sensing technologies are described and assessed. Passive and active sensors at various spatial resolutions (1 m–30 m), and supervised and unsupervised classification methods, are discussed. A novel aspect of this paper is the assessment of monitoring methods and the uncertainty of carbon stock estimation in mangrove forests. The study discusses the advantages and drawbacks of existing methods for mangrove carbon stock measurement and provides recommendations for effective application of blue carbon studies in global markets.
... In green indicators with no data available; orange indicators whit low or medium classification; blue ecosystem services without indicators; gray ecosystem services not relevant in the reference ecosystem. [1] (Blaber, 2002;Feka and Manzano, 2008;UN-REDD, 2014), [2] (Baran, 2000;Blaber, 2002;Ecoutin et al., 2010;Lamptey and Ofori-Danson, 2014), [3] (Feka and Ajonina, 2011), [4] (Lalèyè, 2000), [5] (FAO fisheries and aquaculture department, 2017a; FAO fisheries and aquaculture department, 2017b; FAO fisheries and aquaculture department, 2017c), [6] (Mmom and Arokoyu, 2010;Satyanarayana et al., 2012), [7] (Asibey, 1974;Falconer and Koppell, 1990;Jamnadass et al., 2015) [8] (Komiyama et al., 2008), [9] (Heubach et al., 2011;Heubes et al., 2012;INE são tomé e príncipe, 2014;Ndoye and Tieguhong, 2004;Nkem et al., 2010;Schaafsma, 2012) [10] (Feka and Ajonina, 2011), [11] (Brocard et al., 1998;de Faria et al., 2014;Kersten et al., 1998), [12] (Payet and Obura, 2004), [13] (Joint Research Center and NCEA, 2016), [14] (Ajonina et al., 2014b;Njana et al., 2018;UN-REDD, 2014), [15] (Mitsch et al., 2010), [16] (Lal, 2005;Sanogo et al., 2016), [17] (Khiteka and Kitheka, 1998;Roger et al., 2011), [18] (Li et al., 2005), [19] (Anayah et al., 2013;Chapas and Rees, 1964;Nizinski et al., 1994), [20] (Kamau, 1998), [21] (Bah et al., 2019;Healey et al., 1988), [22] (Roger et al., 2011), [23] (Anayah et al., 2013;Edmunds, 1990;Takounjou et al., 2011), [24] (Vitousek and Sanford, 1986), [25] (Ajonina et al., 2014a;Mallon et al., 2015;UN-REDD, 2014;UNEP, 2011), [26] (Mallon et al., 2015), [27] (Agyeman et al., 2019;Mallon et al., 2015) [28] (Alongi and Mukhopadhyay, 2015), [29] (Knoppers, 1994), [30] (Clark et al., 2001;Folega et al., 2015;Lo Seen Chong et al., 1993), [31] (Adepetu and Corey, 1977), [32] (Joint Research Center, 2018), [33] (Adite et al., 2013;Gajdzik et al., 2014;Kimani et al., 1996;Wright, 1986) [34] (Louca et al., 2009) Frontiers in Environmental Science | www.frontiersin.org February 2021 | Volume 9 | Article 501673 associated with aspects such as conservation status. ...
Mangroves are some of the most productive coastal systems on the planet and provide valuable ecosystem services (ES). They are especially important in threatened ecosystems and developing countries, where they are likely to have direct impacts on local communities. An approach based on ES allows assessing ecosystems across the domains of ecology, sociology and economy. This study focused on the evaluation of ES in mangroves and started by creating a comprehensive global list of mangrove ES based on the Millennium Ecosystem Assessment. These services were then quantified using the best available indicators for mangrove systems. The mangroves of Diogo Nunes, São João dos Angolares and Malanza, located in the São Tomé Island, were used to illustrate the challenges in applying ES indicators in this type of ecosystems. The obtained results confirmed that mangroves can provide important and diverse services. However, the high variability among mangrove systems affects their ability to deliver ES, requiring caution for the extrapolation across regions. This assessment emphasizes how the ES framework can be used as a tool to develop management plans that integrate conservation goals and human wellbeing.
... The integrity of this ecosystem has changed at an alarming rate due to natural and anthropogenic influences (for example, extreme weather events, relative sea-level rise, absence of appropriate legislation, deforestation for fish smoking, the proliferation of invasive species, installation of shrimp and fish ponds, agro-industrial chemicals, petroleum, and gas exploitation). Studies (Ajonina and Usongo, 2001;Ajonina et al., 2014;Donato et al., 2011) have reported that the global area of mangrove forests has declined by 30-50% with about over 20-30% recorded for West and Central Africa over the past half-century. ...
Worldwide, there has been a drastic decline in mangrove ecosystems; hence, there is a need for information on the spatiotemporal characteristics of mangrove ecosystems to inform sustainability efforts. This study sought to provide information to bridge the knowledge gaps on spatiotemporal mangrove distribution in the Mesurado Wetland by analyzing three distinct years (1986, 1998 and 2020). Landsat 8 and Landsat 5 for supervised classification to classify mangrove forest cover within the region of interest (ROIs) were employed to achieve the study goal. The classification done on the three distinct years had an accuracy of 84.83, 93.27, and 92.01% and kappa coefficient of 0.80, 0.92, and 0.88, respectively. The analysis indicated a continuous decline in the mangrove forest cover overall for the thirty-four years (1986-2020) studied-a loss of 10.83% (1986 and 1998) and 24.73% (1998 and 2020); however, most of the decline was experienced from patches within other zones surrounding the Mesurado wetland. Consequently, a total mangrove forest loss amounting to 32.88% at an extrapolated decline rate of 0.96% yr-1 was recorded for the study period (1986-2020). Three of the ten zones, including Central Monrovia, Clara Town, and Old road losing 100% of the mangrove patches between 1986 and 2020, with the rest still experiencing a continuous decline. This study's findings can be used as the basis for policy development, sustainability planning, and restoration activities for the mangrove forest cover in the county.
... Les recherches récentes indiquent que les mangroves aériennes et subaériennes contribuent de façon majeure au stockage de carbone, élément qui alimente les changements climatiques. Les sols de cet écosystème, qui font l'objet des plus récentes publications (Ajonina et al., 2014;Kaufman, 2014Kaufman, et 2009Cohen et al., 2013;Fatoyinbo & Simard, 2013), sont composés de boue ou de vase et parfois de sable. Ils sont riches en carbone (1093 Mg C ha-1 pour le nord Gabon ; Kauffman et Bhomia, 2017), nitrogène, méthane et matière organique. ...
ENGLISH : Despite all the services they provide, Gabonese mangroves are threatened by degradation and deforestation. In this context, this study examines the mangroves dynamics of Libreville and its region (Gabon) in order to identify recent and predict future changes. But also to characterize these mangroves in terms of structural, physico-chemical and floristic parameters. Combining field and remote sensing methods, the project Modelling the dynamics of the Libreville mangroves and its surroundings and the risks of their degradation (MDMLERD) identified, in order of importance, Rhizophora harrisonii, Rhizophora racemosa, Avicennia germinans, Laguncularia racemosa, Conocarpus erectus and Phoenix reclinata. The diameter distribution shows a dominance by young trees, whose height varies between 0 and 5 m. The highest mangroves are located in the eastern part of the Komo estuary and reach up to 55m (remote sensing measurement) and just over 70 m (field measurement). The four main species total 150 512 tons of aerial biomass and an underground biomass of approximately 3 tons. The mangroves of Libreville and its surroundings are dominated by healthy trees (83.13%) while degraded mangroves remain low (16.87%). Overall, the mangrove recorded surface gains totalling 49.71 km², compared with losses of 86.01 km². The 2028 simulation announces the continuation of area loss. This study led to the development of a new methodology for assessing the health status of mangroves, to the mapping of mangrove species and heights, and to highlighting the degradation resulting from natural or anthropogenic processes.
FRANÇAIS : Les mangroves du Gabon sont menacées par la dégradation et la déforestation. Dans ce contexte, a été étudiée la dynamique des mangroves de Libreville et sa région afin, d'une part, d’identifier les changements récents et prévoir les changements futurs et, d'autre part, de caractériser ces mangroves en termes de paramètres structuraux, physico-chimiques et floristiques. Couplant les méthodes de terrain et de télédétection, le projet « Modélisation de la dynamique des mangroves de Libreville et ses environs et des risques de leur dégradation » (MDMLERD) a recensé, dans l’ordre d’importance, Rhizophora harrisonii, Rhizophora racemosa, Avicennia germinans, Laguncularia racemosa, Conocarpus erectus et Phoenix reclinata comme espèce accompagnatrice. La distribution des diamètres des individus montre une courbe dominée par des jeunes, dont la hauteur varie entre 0 et 5 m, et qui se répartissent sur toutes les zones. Les mangroves les plus hautes sont situées dans la partie est de l’estuaire du Komo et atteignent jusqu’à 55 m (mesure par télédétection), et à un peu plus de 70 m (mesure terrain). L’ensemble des quatre espèces principales totalisent 150 512 tonnes de biomasse aérienne, et une biomasse souterraine de 3 tonnes environ. Les mangroves de Libreville et ses environs sont dominées par les arbres encore en bonne santé (83,13%), alors que les mangroves dégradées restent faibles (16,87%). Dans l’ensemble, la mangrove a enregistré des gains de surface totalisant 49,71 km2, contre des pertes de 86,01 km2. La simulation de 2028 annonce la poursuite d’une perte de superficie. Cette étude a permis de développer une nouvelle méthodologie d’évaluation de l’état de santé des mangroves, de cartographier les espèces et les hauteurs, et de mettre en relief les dégradations, selon que l’on soit en face de processus naturels ou anthropiques.
... Cette dernière variable est d'autant plus importante que le bois constitue plus de 70% des sources d'énergie domestique en Afrique (REPAR Cameroun, 2009). Ajonina et al. (2014) ont évalué les stocks de carbone dans les forêts de mangroves et en ont estimé la biomasse totale à 825 Mg / ha. Cette perte de superficie des mangroves affecte ainsi la capacité de ces écosystèmes à séquestrer le carbone et donc, à contribuer à la régulation du climat global. ...
RESUME Face aux changements climatiques et leurs impacts sur le milieu côtier, les écosystèmes de mangrove apparaissent particulièrement vulnérables. La dynamique marine, l'érosion côtière et les pressions anthropiques sont autant de menaces qui pèsent sur ces écosystèmes. Cette étude se propose d'évaluer, à partir de l'analyse diachronique des images satellitaires Landsat et des enquêtes de terrain, la vulnérabilité aux changements climatiques de la réserve de mangrove de Mabe, située à l'embouchure du fleuve Moungo dans la Région administrative du Littoral (Cameroun). La méthodologie utilisée s'appuie sur le traitement et la classification des images Landsat TM et ETM, couplés aux données d'observations et d'enquêtes de terrain. Il en ressort que les mangroves ont enregistré une dégradation totale de 13% en 28 ans, soit une perte annuelle de 0,48%. L'érosion côtière s'est accentuée, induisant une dynamique régressive du trait de côte. Une perte en superficie est donc constatée et estimée à 103 ha (1,03km²). La nécessité de réguler l'installation des pécheurs et la conception des technologies modernes de fumage de poisson s'impose, afin de limiter la consommation en bois de mangrove.
ABSTRACT In the face of climate change and its impacts on the coastal environment, mangrove ecosystems are particularly vulnerable. Sea dynamics, coastal erosion and anthropogenic pressures are among the threats these ecosystems face. This study aims to assess the vulnerability to climate change of the Mabe Mangrove Reserve located at the mouth of the Moungo River in the Littoral Region of Cameroon, based on the diachronic analysis of Landsat satellite imagery and field surveys. The methodology used is based on the processing and classification of Landsat TM and ETM images, coupled with field observations and surveys. As a result, mangroves recorded a total degradation of 13% in 28 years, representing an annual loss of 0.48%. Coastal erosion has intensified, leading to a regressive dynamic of the coastline. A loss in area is therefore observed and estimated at 103 ha (1,03 km²). The need to regulate the installation of fishermen and the development and adoption of modern fish smoking technologies is necessary in order to limit the consumption of mangrove wood for fish drying.
... One recent discovery was the huge amounts of carbon stored in what has been termed "ocean margins," with some estimates suggesting that coastal estuaries, wetlands and mangroves reach as high as 90 percent of global carbon burial(Bauer et al. 2013). For example, studies of mangroves in the Indo-Pacific found an average 1,023 Mg/ha(Donato et al. 2011), while healthy mangroves in four Central African countries stored 1520± 164 Mg/ha(Ajonina et al. 2014). ...
Tropical forests exert a more profound influence on weather patterns, freshwater, natural disasters, biodiversity, food, and human health – both in the countries where forests are found and in distant countries – than any other terrestrial biome. This report explains the variety of environmental services tropical forests provide and the science underlying how forests provide these services. Tropical deforestation and degradation have reduced the area covered by tropical forests from 12 percent to less than 5 percent of Earth’s land area. Forest loss and degradation has reduced or halted the flows of a wide range of ecosystem goods and services, increasing the vulnerability of potentially billions of people to a variety of damaging impacts. Established and emerging science findings suggest that we have substantially underestimated the global importance of tropical forests and the impacts of their loss on human well-being.
... All rights reserved. Mangrove soils were the largest repository of C stocks in Bhitarkanika mangroves; this reflects results seen in mangroves around the world (Kauffman et al. 2009, Murdiyarso et al. 2009, Alongi 2012, Adame et al. 2013, Ajonina et al. 2014, Jones et al. 2014, Tue et al. 2014 ). The average soil C stocks within 0- 100 cm soil depth for the studied land use types (56 to 111 Mg C ha -1 ) were lower in comparison to C stocks in other mangrove forests for same depth. ...
Increased sea level is the climate change effect expected to have the greatest impact on mangrove forest survival. Mangroves have survived extreme fluctuations in sea level in the past through sedimentation and belowground carbon (C) accumulation, yet it is unclear what factors may influence these two parameters. We measured sedimentation, vertical accretion, and belowground C accumulation rates in mangrove forests from the Republic of Palau and Vietnam to examine how diversity (high-Vietnam vs. low-Palau), land use, and location (fringe vs. interior) might influence these parameters. Land use in this study was identified as disturbance and restoration for all mangrove forests sampled in Palau and Vietnam, respectively. Vertical accretion rates were significantly greater in Vietnam (2.44 ± 1.38 cm/year) than Palau mangrove forests (0.47 ± 0.08 cm/year; p < 0.001, F1,17 = 24.96). Vertical accretion rates were positively correlated to diversity (R = 0.43, p < 0.05). However, stronger correlations of accretion to bulk density (R = 0.64, p < 0.01) and significantly higher bulk densities in Vietnamese (0.67 ± 0.04 g/cm3) than Palau mangroves (0.30 ± 0.03 g/cm3; p < 0.001, F1,17 = 54.4) suggests that suspended sediments played a greater role in mangrove forest floor maintenance relative to sea level rise. Average vertical accretion rates were similar between naturally colonized (1.01 ± 0.10 cm/year) and outplanted sites (1.06 ± 0.05 cm/year) and between fringe (1.06 ± 0.12 cm/year) and interior mangrove (0.99 ± 0.09 cm/year) in Vietnam. In Palau, vertical accretion rates did not differ between disturbed (0.42 ± 0.11 cm/year) and undisturbed (0.51 ± 0.13 cm/year) mangrove forests and were higher in fringe (0.61 ± 0.15 cm/year) than interior sites (0.33 ± 0.09 cm/year; p = 0.1, F1,7 = 3.45). Belowground C accumulation rates did not differ between any factors examined. C accumulation rates (69–602 gC/m2/year) were similar to those reported elsewhere in the literature and suggest that intact coastal ecosystems play an important role in the global C cycle, sequestering C at rates that are 10–20× greater than upland forests. Assuming vertical accretion rates measured using 210Pb are an effective proxy for surface elevation, the Vietnamese and Palauan mangroves appear to be keeping up with current rates of sea level rise.
... Mangrove soils were the largest repository of C stocks in Honduran mangroves as also seen in mangroves found elsewhere Kauffman et al. 2011;Alongi 2012;Donato et al. 2012;Ajonina et al. 2014;Kauffman et al. 2014;Tue et al. 2014). Mangrove forests are known to have high C burial rates, and a recent analysis of burial rates from different mangrove systems suggested a global mean value of 163 g C m -2 y -1 (Breithaupt et al. 2012). ...
Among the many ecosystem services provided by mangrove ecosystems, their role in carbon (C) sequestration and storage is quite high compared to other tropical forests. Mangrove forests occupy less than 1 % of tropical forested areas but account for approximately 3 % of global carbon sequestration by tropical forests. Yet there remain many areas where little data on the size and variation of mangrove C stocks exist. To address this gap and examine the range of C stocks in mangroves at landscape scales, we quantified C stocks of Honduran mangroves along the Pacific and Caribbean coasts and the Bay Islands. We also examined differences in ecosystem C stocks due to size and structure of mangrove vegetation found in Honduras. Ecosystem C stocks ranged from 570 Mg C ha−1 in the Pacific coast to ~1000 Mg C ha−1 in Caribbean coast and the Bay Islands. Ecosystem C stocks on the basis of mangrove structure were 1200, 800 and 900 Mg C ha−1, in low, medium and tall mangroves, respectively. We did not find significant differences in ecosystem C stocks on the basis of location (Pacific coast, Caribbean coast and Bay Islands) or mangrove type (low, medium and tall). Mangrove soils represented the single largest pool of total C in these ecosystems, with 87, 81 and 94 % at the Pacific coast, Caribbean coast and the Bay Islands, respectively. While there were no significant differences in total ecosystem stocks among mangrove types, there were differences in where carbon is stored. Mangrove soils among low, medium and tall mangroves contained 99, 93 and 80 % of the total ecosystem C stocks. In addition, we found a small yet significant negative correlation between vegetation C pools and pore water salinity and pH at the sampled sites. Conversion of mangroves into other land use types such as aquaculture or agriculture could result in loses of these soil C reserves due to mineralization and oxidation. Coupled with their other ecosystem services, an understanding of the size of mangrove ecosystem C stocks underscores their values in the formulation of conservation and climate change mitigation strategies in Central America.
... While these results contribute to numerous studies which have estimated the above-and below-ground biomass of mangrove trees (e.g., [17,18,37,), the soil stores most of the carbon in mangrove ecosystems and thus soil carbon is important to include in further analyses [14,56,86,87,99,[111][112][113][114][115][116][117][118][119][120][121][122][123][124]. Until very recently, existing soil analysis facilities in Madagascar were only able to provide soil organic carbon (SOC) results based on the conservative Walkley-Black (WB) methodology [89,[128][129][130][131]. ...
Mangroves are found throughout the tropics, providing critical ecosystem goods and services to coastal communities and supporting rich biodiversity. Globally, mangroves are being rapidly degraded and deforested at rates exceeding loss in many tropical inland forests. Madagascar contains around 2% of the global distribution, >20% of which has been deforested since 1990, primarily from over-harvest for forest products and conversion for agriculture and aquaculture. While historically not prominent, mangrove loss in Madagascar’s Mahajamba Bay is increasing. Here, we focus on Mahajamba Bay, presenting long-term dynamics calculated using United States Geological Survey (USGS) national-level mangrove maps contextualized with socio-economic research and ground observations, and the results of contemporary (circa 2011) mapping of dominant mangrove types. The analysis of the USGS data indicated 1050 hectares (3.8%) lost from 2000 to 2010, which socio-economic research suggests is increasingly driven by commercial timber extraction. Contemporary mapping results permitted stratified sampling based on spectrally distinct and ecologically meaningful mangrove types, allowing for the first-ever vegetation carbon stock estimates for Mahajamba Bay. The overall mean carbon stock across all mangrove classes was estimated to be 100.97 ± 10.49 Mg C ha⁻¹. High stature closed-canopy mangroves had the highest average carbon stock estimate (i.e., 166.82 ± 15.28 Mg C ha⁻¹). These estimates are comparable to other published values in Madagascar and elsewhere in the Western Indian Ocean and demonstrate the ecological variability of Mahajamba Bay’s mangroves and their value towards climate change mitigation.
... For forest assessment, at Douala in Cameroon, mangrove forest measurements of basal area, mortality and recruitment trends were carried out at nine permanent sample plots of 0.1 ha in size, including incorporation of plots already established (Ajonina 2008) to allow a 7-8 years repeat measurement (Ajonina and Chuyong 2011;Ajonina et al. 2014). In Fiji, similar forest assessments were carried out at Tikina Wai, of forest community structure, height and diameter, and density of seedlings, with measurements repeated 2 years later ). ...
Climate change, particularly its associated sea level rise, is major threat to mangrove coastal areas, and it is essential to develop ways to reduce vulnerability through strategic management planning. Vulnerability has three dimensions of exposure to stresses, associated sensitivity, and related adaptive capacity, and ways to measure components of each were trialled at sites in Africa and the South Pacific to develop an analysis procedure based on ranking. The approaches of the ranking system for vulnerability assessment of mangrove systems integrate biotic and abiotic factors along with human management components, using validated methods previously developed for other research questions. These include determining mangrove forest health, adjacent ecosystem resilience, the extent and effects of human impacts, and the environmental conditions of different mangrove settings. Results of the vulnerability assessment ranking using up to 20 measurements found all sites to have some components of vulnerability. Douala Estuary, Cameroon showed the highest vulnerability, owing to low tidal range, impacts from non-climate stressors, and evidence of moderate seaward edge retreat. Tikina Wai, Fiji showed inherent vulnerability owing to location on a subsiding coastline with a low tidal range, but this was offset by strong local community management capacity. Rufiji Delta, Tanzania showed inherent resilience owing to location on an uplifting coastline with a macrotidal range, but showed vulnerability from human impacts and lower local community management capacity. The most critical components to the vulnerability assessment were found to be exposure components of relative sea level trends and sediment supply, and sensitivity components of forest health, recent spatial changes and net accretion rates. The results provide a baseline against which to establish long-term ongoing monitoring, allowing continued assessment of the complex dynamics of climate change impacts, and providing an information base for strategic management decisions.
... This highlights the importance of mangrove surface soils as soil repositories, and the potential for emission of greenhouse gases upon conversion into some other land use type (Lovelock et al. 2011). Mangrove soils were the largest repository of C stocks in Bhitarkanika mangroves; this reflects results seen in mangroves around the world (Kauffman et al. 2009, Murdiyarso et al. 2009, Alongi 2012, Adame et al. 2013, Ajonina et al. 2014, Jones et al. 2014, Tue et al. 2014). The average soil C stocks within 0–100-cm soil depths for the studied land use types (56–111 Mg C/ha) were lower in comparison to C stocks in other mangrove forests for the same depth. ...
Central Africa’s coastal zones, notably in Cameroon and Gabon, are home to significant mangrove ecosystems that provide vital ecological and socio-economic services. Mangroves in this region are essential for coastal protection, biodiversity support, and the sustenance of local fisheries, which are crucial for the livelihoods of coastal communities. However, industrialization, deforestation, and the expansion of oil exploration and coastal development pose serious threats to these vital ecosystems. Despite these challenges, local communities have shown resilience by adopting traditional ecological knowledge and engaging in community-led mangrove conservation initiatives. These efforts highlight the potential for integrating indigenous practices with modern conservation techniques to ensure sustainable mangrove management. This study explores the biodiversity of Central African mangroves, focusing on species such as Rhizophora spp., Avicennia spp., Laguncularia racemosa, and Bruguiera spp., and their role in carbon sequestration and environmental health. Additionally, it examines case studies of community-driven mangrove restoration projects in Cameroon and Gabon, demonstrating the effectiveness of grassroots involvement in conservation efforts. The study emphasizes the importance of strengthening community resilience through ecosystem-based adaptation and providing policy recommendations for the sustainable management of mangrove forests. Ultimately, this research underscores the necessity of multi-stakeholder approaches, involving governments, NGOs, and local communities, to safeguard the future of Central Africa’s mangrove ecosystems and ensure their long-term resilience against environmental and socio-economic challenges.
Marine Protected Areas (MPAs) are central to Africa’s efforts to conserve marine biodiversity and support sustainable development. This study adopts a scoping review approach, systematically identifying, appraising, and synthesizing relevant literature to inform decision-making. While it focuses primarily on Eastern Africa, the review incorporates insights from other African regions to provide a broader, continent-wide perspective. Through an in-depth examination of scholarly research and practical case studies, the study highlights key findings, persistent challenges, and future directions for enhancing MPA effectiveness. Emphasis is placed on the importance of innovative financing, robust governance, and international collaboration in advancing MPA outcomes. The review also explores the integration of socioeconomic dimensions, indigenous knowledge, and climate change adaptation strategies into MPA planning and management. Region-specific issues—including governance limitations, funding gaps, and the impacts of climate change—are critically examined. The study advocates for continuous research and adaptive management that leverages emerging scientific insights to address evolving threats. The conclusion synthesizes core findings, discusses their policy and practical implications, and proposes pathways for future research and strategic development. Ultimately, this review provides a comprehensive and evidence-based overview of the current status and future potential of MPAs in Africa.
Soil organic carbon (SOC) is important in maintaining soil quality, fertility, and the terrestrial carbon cycle. Advances in technology have heightened global interest in estimating soil carbon sequestration. Assessing SOC stocks at landscape scales faces significant challenges, particularly in mosaic landscape influenced by anthropogenic and environmental factors. These challenges include the limited availability of high-resolution soil data, the high cost and labor intensity of soil sampling, and the difficulty of accurately representing soil heterogeneity using conventional sampling methods. This study investigates the influence of key landscape attributes including soil depth, land use type, slope gradient, and topographic position on SOC stock distribution and associated soil properties at 0 – 20 cm (topsoil) and 20 – 50 cm (subsoil) in the highlands of Cameroon. A total of 320 soil samples collected from a 100 km2 site were analysed in the laboratory. Results reveal that soil depth, land use type, and topographic position influence the distribution of SOC, bulk density (BD), and SOC stocks. Land use and topographic positions interactions significantly impact SOC, coarse fraction (CF), and SOC stocks, reflecting varied human activities and environmental effects across topographic locations. Total SOC stocks for the site are
estimated at 37,571 tons C/ha in topsoil and 57,341 tons C/ha in the subsoil, totalling 94,912 tons C/ha of carbon to a depth of 50 cm. Kriging maps demonstrate a decreasing trend in SOC stocks from west to east, with higher values in lowlands characterized by lower BD and CF, and lower values in mountainous areas. These
findings advance SOC stocks evaluation in the highlands of Cameroon, providing a foundational reference for future assessments to guide landscape restoration initiatives in ecologically fragile ecosystems.
The Chapter provides the definition and concept of multifunctional landscapes in the African context. It also highlights the merits of the different landscape approaches recognizing that no single one can address the needs of all existing African landscapes. Ultimately, the people-centred approach to multifunctional landscape management has the merit for addressing the diverse needs for biodiversity conservation, including climate change, food security and poverty alleviation. In this regard, the principles of Multifunctional Landscape approaches emphasize managing landscapes to achieve the dual purpose of multifunctionality and people-centred sustainable resource conservation. The Chapter highlights different tree-based ecosystem approaches and technologies where trees provide a broad range of ecosystem services that often go beyond their specific habitat, e.g. habitat for pollinators, corridors for wildlife mobility and contribution to the local and global climate systems. It also recognizes traditional tree-based ecosystem management practices across different African landscapes including the tropical forests, savanna woodlands and the Sahel. The selected practices presented in this chapter are neither exhaustive nor meant to be replicated or taken as a blueprint for successful multifunctional landscape approaches, but rather intended to provide a basis for innovation to integrate trees in multifunctional landscapes.
The incessant deployment of climate-malign and unsustainable practices by man is driving the world to the brink of a climate catastrophe. This is evidenced by the recurrence of extreme weather/climate events across the globe. Africa in general and Cameroon in particular is being battered by weather/climate extremes and this is predicted to worsen in the coming years. It is against this background that this chapter looks at the role nature-based solutions can play toward enhancing adaptation to and mitigation of climate change, taking Cameroon as case study. The chapter is based on an in-depth review of 200 empirical research papers in Cameroon. Results show that the main nature-based solutions aiding adaptation to and mitigation of climate change in Cameroon are the tropical rainforest, mangroves, Afromontane or highlands forest, bamboo forest, agroforestry, mono-tree plantations (mainly Eucalyptus, Podocarpus, Cypress, and whistling pine), protected areas, renewable energy notably hydroelectricity and solar energy, community forests, apiculture, analog forestry, botanic gardens, organic farming, ecotourism, as well as urban gardens and green spaces. With this plethora of nature-based solutions in Cameroon, there is the need for more action and better policies geared toward scaling up these sustainable and climate-smart practices, as this will go a long way to enhance adaptation to and mitigation of climate change in Cameroon.
The aboveground contributions of mangroves to global carbon sequestration reinforce the need to estimate biomass in these systems. The objective was to determine the aboveground biomass storage and quantify the carbon and CO2e content in Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa present in southeastern Mexico. Based on the Forest Protocol for Mexico Version 2.0 methodology, published by Climate Action Reserve, 130 circular plots were randomly selected and established in an area of 930 ha of mangrove vegetation, and the aboveground biomass and stored carbon were determined. The mangrove had a density of 3515 ± 428.5 individuals per hectare. The aboveground biomass of the three species was 120.5 Mg ha⁻¹. The biomass of L. racemosa was 99.5 Mg ha⁻¹, which represents 82.6% of the total biomass. The biomass of R. mangle was 20.33 Mg ha⁻¹, and that of A. germinans was 0.32 Mg ha⁻¹. The total carbon retained in the trees was 60.25 Mg C ha⁻¹ and 221.1 Mg CO2e ha⁻¹. Laguncularia racemosa generated the highest contributions of CO2e. The area of mangroves accumulated 112,065 Mg of aboveground biomass. The carbon contained in this biomass corresponds to 205,623 Mg CO2e. This mangrove contributes to mitigating the effects of climate change globally through the reduction in greenhouse gases.
Mangroves are considered to be one of the unique ecosystems of the world. They are known for providing protection against the disastrous cyclones that originate in the Bay of Bengal during every pre-monsoon and post-monsoon cyclone season. Hence, they act as the lifeline of the people residing in the coastal areas and in its close proximity. However, mangroves are being destroyed rapidly due to climate change, cyclone-induced flooding, and large-scale anthropogenic interference. The present research makes an attempt to gained insight into the changing nature of the mangroves of the Sagar Island in the South 24 Parganas district of West Bengal both on a qualitative and quantitative basis. The study has used GIS and remote sensing technology and satellite images in both Landsat and Sentinel 2A for the years 2023 for this purpose and employed the Fuzzy Analytical Hierarchy Process (FAHP) to generate the mangrove health diversity model. The study has also computed MABAC for the detection of moisture status within the mangroves and land surface emissivity rate from the mangrove dominated soil. The results reveal a significant decline in the health as well as quantity and density of mangrove forests of Sagar Island with time, and hence, there is an urgent need to take preventive measures to save the coastal lifeguards. The study also states that the involvement of local people and utilization of their ecological knowledge will be the most effective tool to save the mangroves.
Mangroves occur in coastal settings of estuaries, deltas, lagoons, open coasts and oceanic low islands. In these settings, mangrove attributes are influenced by physical factors of temperature, coastal typology, ocean currents and land barriers, wave action and sediment supply, river catchment discharge and sediment yield, and tidal range and inundation frequencies. Factors of gradients and tidal ranges control the lateral extent of mangroves through inundation frequency, and factors influencing accretion rates in the context of relative sea level change can shift or eliminate mangrove extents over time. Mangroves are however resilient systems within steady state equilibrium, that allows recovery from minor perturbations. Factors influencing mangroves can however exceed tipping points of tolerance, bringing a sudden change in ecosystem function and breakdown of equilibrium. Stressors that may cause critical reduction of mangrove resilience are the impacts from humans, climate becoming significantly drier, increased inundation, reduced sedimentation supply, and relative sea level rise. Rehabilitation can be successful if ecological guidance on mangrove restoration is followed, particularly topographic positioning with respect to tidal inundation frequency factors. Understanding of the physical factors that influence mangrove ecosystems that contribute to variation in processes, that result in spatial and temporal differences in mangrove attributes, is essential to effective management.
Mangroves are recognized for their valued ecosystem services to coastal areas, and the functional linkages between those services and ecosystem carbon stocks have been established. However, spatially explicit inventories are necessary to facilitate management and protection of mangroves, as well as providing a foundation for payment for ecosystem service programs such as REDD+. We conducted an inventory of carbon stocks in mangroves within Pongara National Park (PNP), Gabon using a stratified random sampling design based on forest canopy height derived from TanDEM-X remote sensing data. Ecosystem carbon pools, including aboveground and belowground biomass and necromass, and soil carbon to a depth of 2 m were assessed using measurements and samples from plots distributed among three canopy height classes within the park. There were two mangrove species within the inventory area in PNP, Rhizophora racemosa and R. harrisonii. R. harrisonii was predominant in the sparse, low-stature stands that dominated the west side of the park. In the east side of the park, both species occurred in tall-stature stands, with tree height often exceeding 30 m. Canopy height was an effective means to stratify the inventory area, as biomass was significantly different among the height classes. Despite those differences in aboveground biomass, the soil carbon density was not significantly different among height classes. Soils were the main component of the ecosystem carbon stock, accounting for over 84% of the total. The ecosystem carbon density ranged from 644 to 943 Mg C ha⁻¹ among the three height classes. The ecosystem carbon stock within PNP is estimated to be 40,588 Gg C. The combination of pre-inventory information about stand conditions and their spatial distribution within the assessment area obtained from remote sensing data and the spatial decision support system were fundamental to implementing this relatively large-scale field inventory. That work exemplifies how mangrove carbon stocks can be quantified to augment national C reporting statistics, provide a baseline for projects involving monitoring, reporting and verification (i.e., MRV), and provide data on the forest composition and structure for sustainable management and conservation practices.
Background
Mangrove forests have gained recognition for their potential role in climate change mitigation due to carbon sequestration in live trees, and carbon storage in the sediments trapped by mangrove tree roots and pneumatophores. Africa hosts about 19% of the world’s mangroves, yet relatively few studies have examined the carbon stocks of African mangroves. The available studies report considerable differences among sites and amongst the different pools of carbon stocks. None considered the effects of seaward distance. We present details of AGC and SOC carbon stocks for Lindi in Tanzania, and focus on how these values differ with increasing seaward distance and, how our results compare to those reported elsewhere across Africa.
Results
AGC ranged between 11 and 55 Mg C ha⁻¹, but was not significantly affected by seaward distance. SOC for 0–1 m depth ranged from 154 to 484, with a mean of 302 Mg C ha⁻¹. SOC was significantly negatively correlated with seaward distance. Mangrove type (estuarine/oceanic), soil erosion, soil depth may explain these differences We note important methodological differences in previous studies on carbon stocks in mangroves in Africa.
Conclusion
This study indicates that seaward distance has an important effect on SOC stocks in the Lindi region of Tanzania. SOC should be fully incorporated into national climate change mitigation policies. Studies should report seaward distance and to describe the type of mangrove stand to make results easily comparable across sites and to assess the true value of Blue Carbon in Africa. We recommend focusing on trees > 10 cm diameter for AGC, and sampling soils to at least 1 m depth for SOC, which would provide a more complete assessment of the potentially considerable mangrove carbon store.
Of the numerous ecosystem services mangroves provide, carbon storage is gaining particular attention for its potential role in climate change mitigation strategies. Madagascar contains 2% of the world’s mangroves, over 20% of which is estimated to have been deforested through charcoal production, timber extraction and agricultural development. This study presents a carbon stock assessment of the mangroves in Helodrano Fagnemotse in southwest Madagascar alongside an analysis of mangrove land-cover change from 2002 to 2014. Similar to other mangrove ecosystems in East Africa, higher stature, closed-canopy mangroves in southwest Madagascar were estimated to contain 454.92 (±26.58) Mg·C·ha⁻¹. Although the mangrove extent in this area is relatively small (1500 ha), these mangroves are of critical importance to local communities and anthropogenic pressures on coastal resources in the area are increasing. This was evident in both field observations and remote sensing analysis, which indicated an overall net loss of 3.18% between 2002 and 2014. Further dynamics analysis highlighted widespread transitions of dense, higher stature mangroves to more sparse mangrove areas indicating extensive degradation. Harnessing the value that the carbon stored within these mangroves holds on the voluntary carbon market could generate revenue to support and incentivise locally-led sustainable mangrove management, improve livelihoods and alleviate anthropogenic pressures.
Globally, mangrove forests represents only 0.7% of world's tropical forested area but are highly threatened due to susceptibility to climate change, sea level rise and increasing pressures from human population growth in coastal regions. Our study was carried out in Bhitarkanika conservation area (BCA), the second largest mangrove area in eastern India. We assessed total ecosystem carbon (C) stocks at four land use types representing varying degree of disturbances. Ranked in order of increasing impacts these sites included dense mangrove forests, scrub mangroves, restored/planted mangroves and abandoned aquaculture ponds. These impacts includes both natural and/or anthropogenic disturbances causing stress, degradation and destruction of mangroves. Mean vegetation C stocks (including both aboveground and belowground pools; mean ± std. error) in aquaculture, planted, scrub and dense mangroves were 0, 7 ± 4, 65 ± 11 and 100 ± 11 Mg C ha−1, respectively. Average soil C pools for aquaculture, planted, scrub and dense mangroves were 61 ± 8, 92 ± 20, 177 ± 14 and 134 ± 17 Mg C ha−1, respectively. Mangrove soils constituted largest fraction of total ecosystem C stocks at all sampled sites (Aquaculture - 100%, planted - 90%, scrub - 72% and dense mangrove - 57%). Within BCA the four studied land use types covered an area of approximately 167 km2 and the total ecosystem C stocks were 0.07 T g C for aquaculture (~12 km2), 0.25 T g C for planted/ restored mangrove (~24 km2), 2.29 T g C for scrub (~93 km2), and 0.89 T g C for dense mangroves (~38 km2). Although, BCA is protected under Indian wildlife protection and conservation laws, approximately 150,000 people inhabit this area and are directly or indirectly dependent on mangrove resources for sustenance. Estimates of C stocks of Bhitarkanika mangroves and recognition of their role as a C repository could provide an additional reason to support conservation and restoration of Bhitarkanika mangroves. Harvesting or destructive exploitation of mangroves by local communities for economic gains can potentially be minimized by enabling these communities to avail themselves of carbon offset/conservation payments under approved climate change mitigation strategies and actions.
Mangrove forest ecosystems are critically threatened in West-Central Africa due to minimal management and policy efforts. This is partly caused by insufficient knowledge about the economic and ecological value of mangrove ecosystems, which provide important ecosystem services, such as fish, flood prevention, erosion prevention, water regulation, and timber products. A strategy to improve mangrove ecosystem management would be to improve public understanding of the ecosystem's values. We studied these drivers on a regional scale, using socio-economic and grey literature and consultations with experts, thereby focusing on the period from 1980 to 2006. Wood harvesting, conversion of mangroves for agriculture, and bio-fuel plantations were important drivers of mangrove forest change. Coastal development is the most important direct driver of mangrove forest change, especially between 2000 and 2006, a period that coincides with large oil discoveries in the region. About 60% of all industries within the region are located near the coast, which is expected to attract about 50 million people by 2025. Future policies should target the risks of declining mangrove ecosystems in West-Central Africa. This requires focusing on adaptive strategies, reviewing existing coastal and marine ecosystem policies, and developing an integrated coastal management strategy for the region.
The amount of biomass that forests contain determines the quantity of atmospheric emissions that are produced when those forests are cleared and burned. The biomass of tropical forests was previously estimated by extrapolating the results of ecological studies done on small, experimental plots. The value of such studies was limited, however, because the plots were to few in number, were small, had an inherent bias toward large-diameter trees, concentrated on mature forest, were not randomly located, and were not representative of the large forest population of interest.
Coastal wetlands can have exceptionally large carbon (C) stocks and their protection and restoration would constitute an effective mitigation strategy to climate change. Inclusion of coastal ecosystems in mitigation strategies requires quantification of carbon stocks in order to calculate emissions or sequestration through time. In this study, we quantified the ecosystem C stocks of coastal wetlands of the Sian Ka'an Biosphere Reserve (SKBR) in the Yucatan Peninsula, Mexico. We stratified the SKBR into different vegetation types (tall, medium and dwarf mangroves, and marshes), and examined relationships of environmental variables with C stocks. At nine sites within SKBR, we quantified ecosystem C stocks through measurement of above and belowground biomass, downed wood, and soil C. Additionally, we measured nitrogen (N) and phosphorus (P) from the soil and interstitial salinity. Tall mangroves had the highest C stocks (987±338 Mg ha) followed by medium mangroves (623±41 Mg ha), dwarf mangroves (381±52 Mg ha) and marshes (177±73 Mg ha). At all sites, soil C comprised the majority of the ecosystem C stocks (78-99%). Highest C stocks were measured in soils that were relatively low in salinity, high in P and low in N∶P, suggesting that P limits C sequestration and accumulation potential. In this karstic area, coastal wetlands, especially mangroves, are important C stocks. At the landscape scale, the coastal wetlands of Sian Ka'an covering ≈172,176 ha may store 43.2 to 58.0 million Mg of C.
Mangrove forests occur along ocean coastlines throughout the tropics, and support numerous ecosystem services, including fisheries production and nutrient cycling. However, the areal extent of mangrove forests has declined by 30-50% over the past half century as a result of coastal development, aquaculture expansion and over-harvesting. Carbon emissions resulting from mangrove loss are uncertain, owing in part to a lack of broad-scale data on the amount of carbon stored in these ecosystems, particularly below ground. Here, we quantified whole-ecosystem carbon storage by measuring tree and dead wood biomass, soil carbon content, and soil depth in 25 mangrove forests across a broad area of the Indo-Pacific region--spanning 30° of latitude and 73° of longitude--where mangrove area and diversity are greatest. These data indicate that mangroves are among the most carbon-rich forests in the tropics, containing on average 1,023Mg carbon per hectare. Organic-rich soils ranged from 0.5m to more than 3m in depth and accounted for 49-98% of carbon storage in these systems. Combining our data with other published information, we estimate that mangrove deforestation generates emissions of 0.02-0.12Pg carbon per year--as much as around 10% of emissions from deforestation globally, despite accounting for just 0.7% of tropical forest area.
In view of the unique biological characteristics of mangroves, it is interesting to assess the extent to which these ecosystems can be used as indicators of coastal change or sea-level rise. From recent studies of mangrove mortality at several locations (including Guiana, Gambia, Côte d'Ivoire, Kenya, India and Bangladesh), it appears that these coastal ecosystems are so specialized that any minor variation in their hydrological or tidal regimes causes noticeable mortality. Each species of mangrove (but particularly those belonging to the genera Rhizophora, Bruguiera, Sonneratia, Heritiera and Nypa) occurs in ecological conditions that approach its limit of tolerance with regard to salinity of the water and soil, as well as the inundation regime. If the duration of daily immersion were to be modified by tectonic, sedimentological or hydrological events, the species either readjusts to the new conditions or succumbs to unsuitable conditions. Consequently, the use of remote sensing data for mangrove ecosystems offers excellent potential as a tool for monitoring coastal change.
Mangrove forests existing at the interface between the sea and land in inter-tidal zones in tropical and subtropical areas playing quite significant ecological, socioeconomic and climate amelioration functions across the globe have been badly degraded over the years due mainly to human factors. Efforts to manage these forests have been widely demonstrated and documented. While mainly undisturbed states of these forests have been studied, relevant information especially on stock and ecosystem responses to human driven factors is often lacking for management applications. Systems of forest assessments and monitoring often applied to upland forests appear inappropriate to these systems with varied multi-stemmed and diverse eco-morphological structure of tree forms. The main objective of the study was to develop appropriate models to facilitate the assessment, monitoring and sustainable management of mangrove forest resources following different wood exploitation pressures in the Central African coastal Atlantic forests of Cameroon. It is a contribution to the understanding of the recovery dynamics and resilience of mangrove systems to various disturbance systems. Results provided are based on data on temporary sample plots and four year observations with two remeasurements intervals on permanent sample plots established in heavily exploited, moderately exploited and undisturbed mangrove forests in the Douala-Edea Wildlife Reserve mangroves in Cameroon Atlantic coast. Tree diameter dependent allometric relationships were developed to guide sustainable exploitation of mangrove forest including height partitioning relationships, stand curves, tree and stand volume equations with their statistical and graphical fit tests. Tree diameter dependent biomass expansion/conversion factor equations or constants have also been developed based on ratios of tree volumes to total biomass obtained from relevant published generic biomass equations with tables prepared from the best models. These Rhizophora dominated (Rhizophora -rel freq 89.9%, Avicennia germinans (rel. freq. 0.25 %) estuarine mangroves attain maximum height of 59m and diameter of 131.7 cm with mean stand density, basal area and volume of 651 trees/ha, 784 stems/ha (d>=6.4cm), 88.43 m2/ha and 1879m3/ha respectively in well stocked stands. Stand density, basal area, volume and total tree above ground biomass in undisturbed stands varied from 400 - 20100 trees/ha (mean 5416.7, SE 1930.5), 400 - 22300 stems/ha (mean 5900.0, SE 2077.7) (d>=1.0cm); 25.23 - 49.62m2/ha (mean 36.85, SE 3.23); 223 - 611 m3/ha (mean 402.8 and SE 49.4); and 240.3 - 659.3 tons/ha (mean 435.03 SE 53.4) respectively. Standing biomass values are amongst the highest in the world mangroves. Diameter distribution tends to approximate the log-normal type. There were significant site differences in all of the stand parameters (nr-trees, nr-multi-stemmed trees, stand basal area), except incidence of problem trees. There was significant disturbance effect on all stand parameters. Spatial patterns of tree developmental stages and mortality was varied with clump structures dominating. Except for mortality and multi-stemmed trees, there were no significant site, forest disturbance, and census time or interaction differences in spatial patterns in all the tree developmental stages. There were only significant site differences in recruitment and forest disturbance differences in basal area increment. Mean recruitment over the period was generally above mortality. Mortality was highest in heavy exploitation. Disturbance patterns encouraged growth with moderate systems highest. Stand tree density decreases with increasing stem density per tree in an L-shape fashion. Branching intensity for principal mangrove species tend to increase with disturbance and decrease with census time whereas the probability of branching increases with diameter. All the stand parameters (stand density, basal area, volume and above ground biomass) had significant impact on tree form unlike stand growth parameters. Tree recruitment was generally higher than secondary stem recruitment but higher in mortality. Forest dynamics parameters were comparatively higher than examples from uplands forest showing higher resilence of mangroves to disturbance. Dynamics of Avicennia and Rhizophora in balanced mixed stands showed that except in the proportion of multi-stemmed trees that showed significant differences between the two species there were no other differences between species or their tree forms in other stand parameters. Rhizophora generally performed better than Avicennia in mixed balanced stands. The results also show that forest growth, mortality, recruitment and eco-morphological phenomena like probability of branching and root sprouting in Rhizophora can be modelled with linear and binary regression approaches with an established disturbance scale based on proportion of basal area removed with adjacent undisturbed regimes as reference base. The matrix development through multi-stemmed dynamic approach was better than through the traditional diameter distribution approach. The predictive harmony, consistency and convergence of the various models tested through stand table projection approach showed that the models generally predict diameter class distribution with varying accuracies with overestimation of lower diameter classes especially 1-7 cm. Like matrix models, the predictive accuracy of the regression models improved with decreasing forest disturbance with the undisturbed state being the best. A codification system amenable to eco-morphological structure of mangroves is proposed to facilitate field measurements, data processing and easy quantification of population dynamics parameters using spread sheet. The use of the models in setting rotations, planning harvests, yield projections/predictions, assessing impacts of wood extraction or deforestation, planning silvicultural or mangrove restoration operations, forest carbon stock assessments, research, and policy, legal and institutional frameworks for implementation are further elaborated. 1.0. ZUSAMMENFASSUNG Mangrovenwälder, die an der Grenze zwischen Meer und Land in tropischen und subtropischen Ländern wachsen, sind von großer ökologischer und sozio-ökonomischer Bedeutung, zudem sind sie aus Klimaschutzgründen wichtig, jedoch sind sie zum Teil stark degradiert. Bewirtschaftungsmodelle für diese Wälder wurden entwickelt und sind gut dokumentiert. In den meisten Fällen wurden nicht bewirtschaftete Mangrovenwälder studiert, der Einfluss von Bewirtschaftungsmaßnahmen auf das Mangroven-Ökosystem wurde wenig untersucht. Modelle für Inventur und Monitoring von Mangrovenwäldern müssen die komplexen Stammstrukturen der Mangroven berücksichtigen, eine Übertragung von Modellen aus anderen Wäldern ist nicht möglich. Die Zielsetzungen der vorliegenden Untersuchung war Inventur und Monitoringmodelle als Grundlage für die nachhaltige Bewirtschaftung von Mangrovenwäldern an der Atlantik Küste von Kamerun nach unterschiedlichen Störungsregimen zu entwickeln. Die Untersuchungen wurden auf der Grundlage von temporären Stichproben und zweimal wieder vermessenen Stichproben in stark degradierten Flächen, moderat genutzt und auf ungestörten Flächen durchgeführt. 1.1. Allometrische Gleichungen für Inventur und Monitoring von Mangrovenwäldern Allometrische Gleichungen, die vom Durchmesser abhängen, wurden entwickelt, als Grundlage für die nachhaltige Nutzung von Mangrovenwäldern. Umrechnungsfaktoren für Volumen/Biomasse wurden auf der Grundlage von Literaturrecherchen ermittelt und die geeigneten Gleichungen und Tabellen abgeleitet. 1.2. Volumeninventur Die Kosten zur Einrichtung und Aufnahme von permanenten Probeflächen mit Kluppschwelle 1,0 cm war 3 mal so hoch wie die für temporäre Probeflächen mit einer Kluppschwelle von 6,4 cm. Die Wälder, von Rhizophora dominiert, erreichen eine maximale Höhe von 59 m und Durchmesser von 131,7 cm mit einer durchschnittlichen Bestandesstammzahl von 651 Bäumen/ha, 784 Stämme/ha (d>=6.4cm), durchschnittlichen Grundfläche von 88,43 m2/ha und einem Volumen von 1879 m3/ha in gut bestockten Beständen. Bestandesdichte, Grundfläche, Volumen und gesamte oberirdische Biomasse in ungestörten Wäldern variierten von 400 - 20100 Bäumen/ha (Mittel 5416.7, SE 1930.5), 400 - 22300 Stämme/ha (Mittel 5900.0, SE 2077.7) (d>=1.0cm); 25,43 - 49,62 m2/ha (Mittel 36,85), 223-611 m3/ha (Mittel 402,8) und 240,3 - 659 to/ha (Mittel 435,03). Die oberirdische Biomasse nimmt, weltweit gesehen, sehr hohe Werte an, Durchmesser Verteilungen sind Log-Normal mit Weibull Parametern von 1,43 - 2,62 und 25,06 - 39,57. De-Liocourt q-Werte variierten von 0,3 - 5,0 (Mittel 1,5). In den Mangroven-Reinbeständen erwies sich die Zufallsauswahl der Probeflächen als geeignet, eine stratifizierte Auswahl ergab nur eine Effizienzsteigerung von 10%. 1.3 Auswirkungen von Holznutzungen auf Struktur und Dynamik von Mangrovenwäldern Die Bestandesparameter (Stammzahl, Anzahl von Stämmen/Baum, Bestandesgrundfläche) für die Standorte unterschieden sich signifikant. Für alle Bestandesparameter zeigten sich signifikante Unterschiede in Bezug auf die Störungsregime. Aufnahmezeiten hatten keine signifikanten Einflüsse auf die Parameter, die einzige Interaktion zeigte sich für Störungsregime und Auftreten von mehrstämmigen Bäumen. Keine signifikanten Effekte von Standort, Störung, Aufnahmezeiten oder Interaktion konnten in Bezug auf die räumliche Verteilung entdeckt werden. Die einzigen Standort-Unterschiede in Einwuchs und Störungsregime zeigten sich bei Grundflächenzuwachs. Der durchschnittliche Einwuchs in der Untersuchungsperiode war immer größer als die Mortalität. Nutzungen scheinen die Mortalität zu fördern, am größten war sie in Flächen mit großer Nutzung, mittel in mittlerer Nutzung und am geringsten in ungestörten Beständen. Wie zu erwarten, war die Mortalität am höchsten in den unteren Durchmesserklassen, vor allem in der Klasse 1-3 cm. Nutzung im allgemeinen hatte einen Effekt auf den Einwuchs, am höchsten war er bei mäßiger Nutzung, dann hohe Nutzung und dann bei ungestörten Beständen. Die Verteilung des Durchmesserzuwachses war annähernd normal verteilt. 1.4. Auswirkungen von Störungen auf die Stammform Die Bestandesstammzahl nimmt mit zunehmender Anzahl von Stämmen/Baum ab. Die Verästelungen nehmen mit dem Ausmaß der Störungen zu und nimmt mit Nutzungen ab, die hohe Nutzung zeigt 10 Stämme/Baum, moderate 11 und ungestört 4. Alle Bestandesparameter (Stammzahl, Grundfläche, Volumen, Biomasse) hatten einen signifikanten Einfluss auf die Baumform. Es zeigten sich nur Interaktionen von Bestand, Baumform, Nutzungshöhe und Bestandesdichte. Im Allgemeinen wird der Beitrag vom Bäumen mit multiplen Stämmen zu verschiedenen Bestandesparametern (Stammzahl, Grundfläche, Volumen und Biomasse) mit zunehmender Nutzung größer sein, jedoch mit der Beobachtungszeit abnehmen. 1.5. Dynamik von Avicennia und Rhizophora in Mischbeständen Die Bestandeshöhe für Avicennia war 15,4 m und Rhizophora 17,2 m. Mit Ausnahme der Stammverzweigungen ergaben sich keine Unterschiede in den Bestandeswerten für beide Baumarten. Die mittlere Stammzahl/ha für Avicennia war 4139/ha, für Rhizophora 2850/ha, in Mischbeständen 6989/ha. Die Grundfläche für Avicennia war 5,18 m2/ha, Rhizophora 4,86 m2/ha, Mischbestände 10,04 m2/ha, die Biomasse war für Avicennia 31,28 to/ha, Rhizophora 32,0 to/ha und Mischbestand 63,28 to/ha. Es wurden signifikante Unterschiede zwischen Stammform und Baumart und zwischen Recruitment und Mortalität für unterschiedliche Stammformen gefunden. 1.6. Modellierung der Bestandesdynamik von Magrovenwäldern für unterschiedliche Nutzungsregime. Regressions- und Matrix-Modelle wurden zur Modellierung der Bestandesdynamik bei verschiedenen Störungsregimen formuliert. Die Störungsregime wurden definiert über das Verhältnis der ausgeschiedenen Grundfläche zu durchschnittlicher Grundfläche der ungestörten Probeflächen. Lineare und/oder binäre logistische Regression wurde angewendet, um die Modell Parameter zu kalibrieren für a) 4-Jahres Grundflächenzuwachsmodell für Einzelbäume, b) 4-Jahres Mortalitätsmodell für Einzelbäume, c) 4-Jahres Regenerationsmodell d) Bestandesvolumen Projektionsmodell. Zusätzlich wurden grafische Bestandes-Struktur Modelle und Matrix Modelle formuliert. Die Modelle wurden anhand von unabhängigen Datensätzen überprüft. Für die Grundflächenzuwachsmodelle war die abhängige Variable ln (g+1) signifikant abhängig von 1/D, relativer Interaktionsterm D2/AMD, Interaktion von Grundfläche und Nutzungshöhe. Das Modell hat akzeptable Vorhersagegüte (durchschnittliche Prozentdifferenz 0,54%, durchschnittlicher prozentualer Bias - 31,41%. Die Überlebenswahrscheinlichkeit war abhängig von 1/D, relativer Durchmesser, Residual dominante Bestandeshöhe und Nutzungshöhe. Die Wahrscheinlichkeit des Recruitments war eine Funktion der Bestandesdichte, Bonität und Nutzungshöhe. Bestandesvolumen-Projektionsmodelle wurden als Zeit-unabhängige Ertragsmodelle mit 2 Sätzen von unabhängigen Variablen formuliert - Modell 1 - Grundfläche, Bonität und prozentuale Grundflächenentnahme und Modell 2 mit Grundfläche, und prozentuale Grundflächenentnahme. Ein drittes Modell wurde mit Grundfläche, prozentuale Grundflächenentnahme und Zeit seit der letzten Störung definiert. Mehrere morphologische Gegebenheiten wie Verzweigungen und Wurzelausschläge wurden für Rhizophora modelliert. Die Wahrscheinlichkeit von Verzweigungen war abhängig von Durchmesser, relativem Baum Status, Interaktion von Grundfläche und Störungsregime und Zeit seit der letzten Störung. Das Modell zeigt eine gute Anpassung für Durchmesserklassen über 3 cm. Die Wahrscheinlichkeit von Wurzelausschlägen von Rhizophora ist abhängig von relativem Baum-Status, Interaktion von relativer Status und Störungsregime. Das Modell zeigt eine gute Anpassung für alle Durchmesserklassen. Die Liocourt q-Werte zeigen signifikante Differenzen zwischen Baumform, Nutzungslevel und die Interaktionen. Die q-Werte waren höher für alle Nutzungsregime für Stämme im Vergleich zu Bäumen. Die q-werte waren i.a. niedriger bei geringerer Störung und nehmen mit zunehmenden Aufnahmeprozenten zu. Die Matrix Modelle, die Veränderungen bei multiplen Stammformen und der strukturellen Dynamik der Baum Population zeigten, dass die dominanten Eigenwerte für den Anteil von multiplen Stammformen i.a. eins waren, unabhängig von den Nutzungslevels. Dies könnte darauf zurückzuführen sein, dass von Natur aus, ein stabiler Anteil von einzelnen- und multiplen Stämmen, unabhängig von der Nutzung vorhanden ist. Es gab dabei räumliche Variationen, das stabile SS:MS Verhältnis zeigt, dass die Tendenz zu einzelnen Stämmen mit zunehmender Nutzungsintensität steigt. Im Allgemeinen ergab das dynamische Matrix-Modell für multiple Stämme gute Ergebnisse, gefolgt von Einzelstamm-Bäumen und multiplen Stamm Bäumen für die Nutzungsregimes. Die Vorhersagen für die Durchmesserklassen waren Überschätzungen für die unteren Durchmesserklassen, unabhängig von den Nutzungsregimen. Die Genauigkeit der Modelle für die Vorhersage der Durchmesser-Verteilungen war für geringe Störungsregime genauer als für höhere sowohl für Einzelstamm- als auch für multiple Stamm-Modelle. Matrix Modelle der strukturellen Dynamik der Mangroven Bestände zeigten, dass die Struktur sehr variabel war. Mit der Ausnahme von wenigen ungestörten Wäldern haben die meisten Störungsregime und Aggregierungen Eigenwerte größer als 1. Dies weist auf wachsende Populationen hin. Es ergaben sich signifikante Unterschiede zwischen den Eigenwerten von Störungsregimen und Bonitäten. Eigenwerte waren signifikant höher für gestörte Regime als für ungestörte. Stabile Verteilungen für alle Regime und Zonen sind 100.13.3:1:0:0 für die Größen-Klassen 1,2,3,4,5,6,7. Diese Waldstruktur, die mit der größten latenten Wurzel assoziiert ist, maximiert den Waldertrag. Die stabilen Verteilungen waren sehr variabel für Regime und Zonen, in manchen Fällen hatten manche Klassen Nullwerte. Dies zeigt, dass eine ausreichende Verjüngung notwendig ist, um Produktion und Zuwachs des Waldes zu garantieren, während in anderen Fällen Nutzungen den Waldzustand stabilisieren können. Die Vorhersagen der verschiedenen Modelle, die durch die Tabellenkalkulationsprogramme getestet wurden, zeigen, dass die Durchmesserklassen-Verteilungen mit unterschiedlicher Genauigkeit vorhergesagt werden konnten, die unteren Klassen von 1-7 cm jedoch überschätzt wurden. Ähnlich wie bei den Matrix-Modellen ist die Vorhersagegenauigkeit der Regressionsmodelle besser für ungestörte Wälder. 1.7. Anwendungen für die Bewirtschaftung von Mangrovenwälder Diese Modelle können für Simulationen der nachhaltigen Bewirtschaftung von Mangrovenwäldern verwendet werden. Ein Klassifizierungssystem wird vorgeschlagen, um Geländeaufnahmen, Datenverarbeitung und Quantifizierung der Populationsdynamik mit einem Tabellenkalkulationsprogramm zu erleichtern. Die Anwendung der Modelle für die Festlegung der Umtriebszeit, der Planung von Erntemassnahmen, der Projektion/Vorhersage des Ertrags, für die Bestimmung des Einflusses von Holzernten oder Abholzungen, für die Planung von waldbaulichen Massnahmen oder der Wiederbegründung von Mangrovenbeständen, für die Abschätzung der Kohlenstoffspeicherung und für Forschungsarbeiten wird diskutiert, die forstpolitischen, rechtlichen und institutionellen Rahmenbedingungen für die Implementierung werden beschrieben.
Structural parameters of mangrove forests were measured at seven geographical locations in Florida (U.S.A.), Puerto Rico, Mexico, and Costa Rica. One-tenth hectare plots were subdivided into twenty 5 x 10 m plots where all individuals greater than 2.5 cm DBH were measured and recorded. Height of the tallest tree in each plot was measured. The complexity index developed by Holdridge (1967) as an integrative measure that combines floral characteristics (number of species) (s), stand density (d), basal area (b), and height (h) was computed as follows: (s) (d) (b) (h) 10-3. The riverine and basin mangrove forests of the southwestern coast of Florida had considerably taller trees (6-9 m) and larger basal areas (20.3 38.5 m2/ha) than did scrub mangrove growing on the southeastern Coast of Florida where a low canopy (1.0 m), a low basal area (6.0 m2/ha), and a correspondingly low complexity index (1.5) were measured. The riverine forests of the Marismas Nacionales located on the Pacific coast of Mexico had high complexity indices (49.7-73.2) due to the large basal areas (57.8-60.8 m2/ha), tall canopies (16-17 m) and a large number of trees greater than 10 cm diameter (103-145/ha). The entire estuarine system of the Marismas Nacionales acts as a receiving basin for large quantities of freshwater runoff and nutrient-rich sediments from surrounding upland watersheds. Except for local sport fishing, the commercial fishing industry of Florida, Puerto Rico, and Costa Rican mangrove waters is not nearly as active as that observed near Teacapan, Mexico. The structural characteristics of the north- and south-coast mangroves of Puerto Rico are probably best described by the direct and indirect influences of the climate at each coastline. The basin mangrove forest on the humid north coast (annual rainfall of 1631 mm) has a basal area of 17.8 m2/ha, canopy height of 13.6 m, and a complexity index of 16.7. The driest site (rainfall of 860 mm/year) on the south coast of Puerto Rico was a red mangrove fringe forest which had a complexity index of 0.9, low canopy height (7 m), and low basal area (6.9 m2/ha) Here upland runoff, draining into the mangroves through porous limestone outcrops, only occurs 1-2 months annually. In Costa Rica, the riverine mangroves near Puerto Limon on the Caribbean coast (annual rainfall of 3300 mm) are more structurally developed than either the riverine or fringe mangroves of the drier (1800 mm annual rainfall) Pacific coast sites. A basal area of 96.4 m2/ha (primarily Pterocarpus officinalis Jacq.) and a tall canopy (16 m) gave this forest the largest complexity index (84.5) of all forests inventoried. The Pacific coast mangroves of Costa Rica are exposed to seasonal rainfall (six months dry season), and this drier environment was reflected in a shorter canopy (9.5-10.0 m) and a lower basal area (23.2-32.9 m2/ha).
Inventory data on tree weights of 104 individual trees representing 10 mangrove species were collected from mangrove forests in South-East Asia to establish common allometric equations for the trunk, leaf, above-ground and root weight. We used the measurable tree dimensions, such as dbh (trunk diameter at breast height), DR0.3 (trunk diameter at 30 cm above the highest prop root of Rhizophora species), DB (trunk diameter at lowest living branch), and H (tree height) for the independent variable of equations. Among the mangrove species studied, the trunk shape was statistically identical regardless of site and species. However, of each species, when DB2 or dbh2 or DR0.32 was selected as the independent variable. For the root weight, the common equation was derived from the allometric relationship between root weight and above-ground weight, since these two partial weights significantly correlated with each other. Based on these physical and biological parameters, we have proposed four common allometric equations for estimating the mangrove tree weight of trunk, leaf, above-ground part and root.
We present tree community diversity, species composition, basal area and aboveground biomass of three forest types in the Dja Biosphere Reserve, in South-East Cameroon, part of the contiguous tropical forest of the Congo Basin. A total of fourteen, 1-ha, plots were established in heterogeneous terra firme forests (TFF), Gilbertiodendron dewevrei forests (GDF) and periodically flooded forests (PFF). A total of 281 tree species with diameter ≥10-cm were recorded. The Shannon diversity index was significantly higher in TFF (5.7-±-0.28) and PFF (5.6-±-0.23) than in GDF (2.29-±-0.48) (ANOVA, F2,11-=-139.75, P-<-0.001). While tree density did not differ between forest types (F2,11-=-3.50, P-=-0.06), basal area differed significantly (F2,11-=-7.38, P-=-0.009), as did aboveground biomass (F2,11-=-17.95, P-<-0.001). Mean AGB values were respectively, 596.1-±-62.24, 401.67-±-58.06 and 383.14-±-61.91-Mg-ha-1 in GDF, TFF and PFF. Variation in the abundance of trees with large diameter was the main reason for these differences. Few dominant species made the greatest contribution to the AGB. G. dewevrei, accounted for 83% of AGB in GDF, Penthaclethra macrophylla for 9.9% in TFF and Uapaca heudolotii for 10.6% in PFF. The importance of preserving G. dewevrei forest in the context of 'Reducing Emissions from Deforestation and forest Degradation' (REDD) policies is discussed.
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