Article

Riparian forests and biodiversity conservation in Benin (West Africa)

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  • University of Parakou (Université de Parakou)
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... Studies have also shown that riparian forests serve as corridors for maintaining regional biodiversity [19], providing vital links in the landscape for birds and small mammals [20][21][22]. Despite their size in patches, riparian forests are highly complex, diverse, and productive systems of significant ecological, social, and economic values [23][24][25][26]. ...
... e findings of the study reveal that though Taia Riparian forest is under massive pressure from the surrounding communities for services such as fuelwood and charcoal production, however, the forest shows signs of resilience and the potential of maintaining rich biodiversity if protection or conservation methods are instituted ( Figure 5). e results of this finding, however, disagree with the conclusions made by [23,61] that riparian forest demonstrates a high level of biodiversity. Across the West African region, for example, Sambaré et al. [26] recorded a total of 196 species representing 139 genera and 51 families in riparian forests within Burkina Faso. ...
... Across the West African region, for example, Sambaré et al. [26] recorded a total of 196 species representing 139 genera and 51 families in riparian forests within Burkina Faso. Additionally, Natta et al. [23] in Benin republic recorded 1,002 species (about 1/3 of the estimated Benin flora from 120 families and 515 genera in 19 ha with the most species-rich families being Leguminosae, Poaceae, Rubiaceae, Euphorbiaceae, Cyperaceae, Asteraceae, and Acanthaceae, respectively). Similarly, Pereki et al. [62] in Togo also recorded a total of 258 plant species belonging to 119 genera from 63 families in Abdoulaye Wildlife Reserve dry forests. ...
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Riparian forest inventory is essential in understanding the floristic biodiversity and provides necessary information on the growth trend and status of plant diversity along forest ecosystem, especially the riparian forests. is study was undertaken to assess the species diversity, growth status, and bio-volume of Taia riparian forest for community-based conservation intervention. In this study, we enumerated 602 individual trees, which comprised 49 species that belong to 37 genera in 25 families. In total, 14 rectangular plots of dimension 20 × 50 m 2 were demarcated. All trees species within the sampled plots having diameter at breast height [Dbh] ≥7 cm were identified and height measured using the Haga altimeter, girth and measuring tape to determine the growth status. e result shows that 83% of the trees enumerated have [Dbh] that range from 7 to 30 cm, whereas 17% had [Dbh] greater than 30 cm. Funtumia africana and Trichilia heudelotii were the dominant species in almost all aspects in the study area. Meliaceae, Apocynaceae, and Mimosaceae were the dominant families with the highest species. e Shannon diversity index was 3.094, whereas the Simpson and Evenness diversity was 0.9303 and 0.4502, respectively. Other diversity indices estimated were Margalef 7.544, Equitability 0.7949, and Fisher_alpha 12.77. The overall bio-volume was 283.05 m, 3 with a total basal cover of 12.54 m 2. Height and [Dbh] were not significantly correlated with the bio-volume. Biotic pressure such as fuel wood collection, unsustainable charcoal production, pole harvesting, bush fires, and other traditional and cultural functions contributes greatly to the exploitation of the riparian forest. Therefore, urgent strategic conservation and protection measures should be adopted to prevent further degradation of forest ecosystems along river banks in the district and other ecologies in Sierra Leone.
... It provides connectivity to Biligiri Rangan hills Temple (BRT) Sanctuary and Mudumalai Tiger Reserve, which is in conjunction with Mysore-Nilgiri corridor (largest population of Asian elephants is found here) (Sukumar 1989). The major portion of the sanctuary is surrounded by dry deciduous patches, and riparian forests here during dry season assumes a very significant place for wildlife (Natta et al. 2003) particularly to the otters and wide elephant herds found in the sanctuary. In addition, conservation and management of riparian vegetation in the upper reaches, where CWS is located helps to reduce flood velocities and increase the further flow towards lower reaches, thereby maintaining the river water healthier. ...
... The CWS also contains the best habitat and populations for the elephants, as the study area provides connectivity to BRT Sanctuary and Mudumalai Tiger Reserve, which is in conjunction with Mysore-Nilgiri corridor (largest population of Asian elephants is found here) (Sukumar 1989). The major portion of the sanctuary in the present case is surrounded by dry deciduous patches, and riparian forests here during dry season assumes a very significant place for wildlife (Natta et al. 2003) particularly to the otters and wide elephant herds found in the sanctuary. Keeping increasing water scarcity and flood disaster in the lower reaches during monsoon, conservation and management of riparian vegetation in the upper reaches, where CWS is located helps to reduce flood velocities and increase the further flow towards lower reaches, thereby maintaining the river water healthier. ...
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This article highlights the impact of anthropogenic disturbance on forest structure and plant diversity in the riparian forest in the Cauvery Wildlife Sanctuary, Karnataka, Southern India. We clustered 11 transects into groups with low and high anthropogenic disturbances. In total, 73 tree species were recorded on 11 transects, of which 57 species were found in less-disturbed sites and 39 species in high-disturbed sites. Shannon–Wiener diversity confirmed higher values for less-disturbed sites (3.2 ± 0.7) compared with high-disturbed sites (2.7 ± 0.5). Evenness index suggested no complete evenness in the two sites. Mean species richness and number of individuals in the majority girth classes were found to be higher in less-disturbed sites than in high-disturbed sites. Non-native plants dominated the high-disturbed sites. The occurrence of native and non-native species was correlated with the level of disturbance. Current disturbance intensities may have led to loss of native species such as Ixora bracheata, Madhuca latifolia, Syzygium cumini and Terminalia arjuna in riparian forests. This study concludes that species-rich areas in the riparian forests are under threat. Protection of these areas should be prioritized in policy, because anthropogenic disturbance has led to decreasing riparian forest species diversity and structure.
... Studies have also shown that riparian forests serve as corridors for maintaining regional biodiversity [19], providing vital links in the landscape for birds and small mammals [20][21][22]. Despite their size in patches, riparian forests are highly complex, diverse, and productive systems of significant ecological, social, and economic values [23][24][25]. ...
Article
Full-text available
Riparian forests inventory is essential in understanding the floristic biodiversity and provides necessary information on the growth trend and status of plant diversity along forests ecosystem especially the riparian forests. This study was undertaken to assess the species diversity, growth status and bio-volume of Taia riparian forest for community-based conservation intervention. In this study, we enumerated 602 individual trees, which comprised 49 species that belong to 37 genera in 25 families. In total, [14] rectangular plots of dimension 20 x 50m 2 were demarcated. All trees species within the sampled plots having Diameter at Breast Height [Dbh] ≥ 7cm were identified and height measured using the Haga Altimeter, girth and measuring tape to determine the growth status. The result shows that 83% of the trees enumerated have [Dbh] that range from 7-30cm while 17% had [Dbh] greater than 30cm. Funtumia africana and Trichilia heudilotii were the dominant species in almost all aspect in the study area. Meliaceae, Apocyanaceae and Mimosaceae were the dominant families with the highest species. The Shannon diversity index was 3.094 while the Simpson and Evenness diversity was 0.9303, 0.4502, respectively. Other diversity indices estimated were Margalef 7.544, Equitability 0.7949, Fisher_alpha 12.77. The overall bio-volume was 283.05m 3 with a total basal cover of 12,54m2. Height and [Dbh] were not significantly correlated with the bio-volume. Biotic pressure such as fuelwood collection, unsustainable charcoal production, pole harvesting, bushfires, and other traditional and cultural functions contributes greatly to the exploitation of the riparian forest. Therefore, urgent strategic conservation and protection measures should be adopted to prevent further degradation of forest ecosystems along river banks in the District and other ecologies in Sierra Leone.
... The Cauvery river in the lower reaches is is surrounded by dry deciduous to scrub type forests, and moist deciduous to semi-evergreen type trees along the river bank. Since the riparian zone stands distinctly here by harboring moist deciduous to semi-evergreen type vegetation, during dry season they assumes a very significant place for wildlife (Natta et al. 2003) particularly to the otters and wide elephant herds found in the sanctuary. But, the riparian vegetation here stands in high risk areas, as there is a chance of invasion of several pioneer species resided in the adjoining dry deciduous and scrub type vegetation into the riparian areas (Manjunath, 2001). ...
Chapter
Riparian forests (RF) composition is important for moderating climate change impacts on agricultural watersheds. However, they are under threat from deforestation of catchment areas. The study used remote sensing techniques and field inventorying to assess woody species composition of RF on farmland (FA) and protected area (PA) along Afram rivercourse in the humid savanna of Ghana. Analysis of Landsat images revealed a reduction in forest cover from 1986 (50 %) to 2014 (31 %) in the river catchment. Ground survey of 60 randomly selected plots (500 m2 per plot) equally divided between FA and PA along the river in a 50 m buffer zone showed a reduction in the number of woody species (diameter ≥5 cm) from PA (58) to FA (39). Shannon-Wiener Index for species diversity also reduced from PA (3.8 ± 0.05) to FA (3.1 ± 0.08). Diameter class distribution of species of both PA and FA showed a reversed J-shaped curve indicating successful regeneration. Reduction in species density per hectare from PA (545 ± 18) to FA (277 ± 13) is likely to increase the surface exposure of the riparian area in FA. This will heighten risks of climate disasters such as fires and flooding. Education of farmers on the importance of riparian forests may ensure their protection.
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Riparian forest buffers (RF) are integrative part of the savanna agricultural landscape. However, they are under threat of deforestation from agricultural intensification. To ascertain the impact of the deforestation, this study used remote sensing techniques and field inventorying to assess riparian woody plant diversity on farmland (FA) and forest reserve (FR) along Tankwidi rivercourse in the Sudanian savanna of Ghana. Post-classification analysis of Landsat images revealed a reduction in forest cover from 1986 (23%) to 2014 (7%) in the river basin. Ground survey of sixty randomly selected plots (500 m 2 per plot) equally divided between FA and FR along the river in a 50 m buffer zone showed a reduction in the number of woody species (diameter ≥ 5 cm) from FR (40) to FA (19). Anogeissus leiocarpus and Mitragyna inermis were the most abundant species in both FR and FA. Shannon-Wiener Index for species diversity reduced from FR (2.5±0.09) to FA (1.8±0.14). Within FR, there were more species (58%) in the lower diameter class (5 to 15 cm) than the higher diameter classes (15 to 50 cm) suggesting successful regeneration. The reverse was observed in FA where the individuals in the lower diameter class were fewer (26%) than the higher diameter classes. Reduction in species density from FR (355±21) to FA (146±11) will increase the surface exposure of the riparian area in farmland to heighten risks to climate disasters such as fires and flooding. Managing the risks will not be possible unless a conscious effort is made to educate farmers on the roles of RF, replanted to enhance diversity or riparian buffer excluded from farming for vegetation recovery.
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The present research deals with the flora, phytosociology and ecology of riparian forests. The overall objective of this research is to contribute to a better knowledge of the flora, diversity and ecology of riparian forests in Benin . The specific objectives are to (a) compile a preliminary riparian forests plant species list, (b) assess plant species and ecosystem diversities, (c) investigate plant communities, (d) clarify the structural and floristic relationship of riparian forests with adjacent plant communities, and (e) assess the ecology of certain endangered tree species in riparian forests. In chapter 1 (General introduction), the research background, objectives and approach for riparian forests biodiversity assessment, and the organisation of the thesis are presented. Chapter 2 introduces the study area which covered about 70 % of Benin , from 7 ° 10' to 12 ° 20' N. Chapter 3 presents an overview of riparian forests biodiversity, their importance and the threats they face making them endangered ecosystems. A definition of riparian forests (or gallery forests) is given in the Benin context. The floristic characteristics of riparian forests in each phytogeographic district are presented. Issues related to legal protection and rehabilitation of the function and resources of riparian forests are documented: specifications and weaknesses of the forest law regarding riparian forests are presented; challenges for various stakeholders are discussed, and some improvements of the current forest law are proposed. Chapter 4 assesses plant species diversity, as well as species abundance models that best fit representative collections of plant species of riparian forests throughout the country. This study shows the richness and diversity of riparian forests in Benin , in comparison to other vegetation types in this country. They harbour about 1/3 of the estimated total number of plant species of the whole country in sample plots totalling 19 ha. This flora shares many features with riparian forests and dense forests worldwide: e.g. most abundant families, species richness/ha, trees species richness/ha, Shannon index, equitability index of Pielou, and species abundance models. Endemism is very low compared to that in rain forests, what is not surprising in the Dahomey Gap. The main conclusion is that relatively large numbers of species are still maintained in small forest fragments along waterways. These remnants with their specific plant species composition can be used for the restoration of degraded forest stands. Chapter 5 assesses the structure and ecological spectra of 19 ha of riparian forests through selected parameters (e.g. life form, geographic affinity, diameter class distribution, basal area, stem density, species dominance) that give a general picture of different vegetation types present. Figures obtained for these parameters show that riparian forests in Benin are on the one hand similar to many riparian forests in West Africa as well as in South and Central America, and on the other hand to many tropical upland forests. A brief description of the process of riparian forests degradation is also presented. Chapter 6 deals with the phytosociological assessment of representative relevés of riparian forests of Benin . Floristic ordination (DCA analysis) and classification (TWINSPAN) were derived from a comprehensive floristic inventory of a data set of 818 plant species and 180 relevés. This yielded 12 plant communities or associations, most of which had not yet been formally described: 1 - Community of Isolona thonneri and Callichilia barteri (10 relevés) along streams. This community occurs at the lowest parts of the gallery forest with frequent inundation in the centre of Pénéssoulou protected forest. 2 - Community of Motandra guineensis and Pararistolochia goldieana (24 relevés) along streams at the East and West parts of Pénéssoulou reserve forest. This community is mainly present on drained sites ( i.e . seldom inundated). 3 - Community of Chrysobalanus icaco subsp . atacoriensis and Pentadesma butyracea (22 relevés) along streams at hill feet in the Atacora mountain chain. 4 - Community of Alchornea cordifolia and Ficus trichopoda (9 relevés) along streams on regularly inundated plateaus all over the country. 5 - Community of Berlinia grandiflora and Khaya senegalensis (8 relevés) along streams on drained plateaus ( i.e . seldom inundated), mainly in the Sudanian region of the country. 6 - Community of Raphia sudanica and Oxytenanthera abyssinica (8 relevés) along streams on drained plateaus, mainly in the Sudanian region. 7 - Community of Cynometra megalophylla and Parinari congensis (31 relevés) along the Ouémé river in the Guinean region of Southern Benin . 8 - Community of Capparis thonningii and Crateva adansonii (30 relevés) along the Ouémé river in the Sudano-Guinean region of Central Benin . 9 - Community of Lepisanthes senegalensis and Drypetes floribunda (17 relevés) along the Ouémé river in the Sudano-Guinean region of Central Benin . 10 - Community of Uapaca heudelotii and Irvingia smithii (8 relevés) along the Sota river in the Sudanian region of North East Benin. 11 - Community of Garcinia livingstonei and Combretum acutum (12 relevés) along the Pendjari river in the Sudanian region of North West Benin. 12 - Community of Mimosa pigra and Ficus asperifolia (20 relevés) widely distributed on sandy banks along rivers. Ordination proved invaluable in the exploration of environmental characteristics of the phytosociological groups. The environmental factors (waterways, relief, topography, latitude and longitude) helped in the grouping of floristic relevés in the above mentioned 12 plant communities. The distinguished plant communities were compared with syntaxonomic data in literature. Riparian forests in Benin belong to the Mitragynetea Schmitz 1963, which is the phytosociological class of hygrophile fresh water forests of tropical Africa . Based on similarities of ecological conditions and floristic composition, the 12 plant communities can be classified into 3 orders that are Alchornetalia cordifoliae Lebrun 1947, Lanneo-Pseudospondietalia Lebrun & Gilbert 1954 and Pterygotetalia Lebrun & Gilbert 1954. Chapter 7 presents the spatial distribution and ecological factors determining the occurrence of Pentadesma butyracea (Clusiaceae), a rain forest and multipurpose species found in Benin only along certain streams. Among the 224 tree species found along waterways, Pentadesma is one of the least known, yet of great ecological and economic importance. Field survey reveals the presence of this rain forest species in four non-contiguous remnant riparian areas, some located far from its optimal ecological range. If urgent actions are not taken to protect the remaining fragmented and dispersed riparian habitats, current human-induced disturbance could result in the disappearance of this species in Benin . Chapter 8 deals with the variation of the floristic composition, structural parameters (e.g. abundance, average height, basal area, tree richness) and spatial distribution of tree species at river edges across riparian forests. Horizontal and vertical structures of tree species exhibit complex patterns at riverside. On the one hand, tree stems are characterised by an uneven distribution across riparian forests, on the other hand height and basal area variations at riverside do not show any easily interpretable patterns. The numerical analysis confirms a gradual variation in the floristic composition across riparian forests and neighbouring plant communities. These results suggest a partitioning of riparian forests in three habitats ( i.e. river front, middle and riparian forest edge). An implication for diversity assessment is that plot size, shape and layout in the terrain should take into account the river front, the middle and the edge of riparian forest. Due to the non-coverage of the whole riparian forest width and unequal chance of species and stems to be sampled, circular and square plots are not suitable for structural parameters and phytodiversity assessment in riparian forests. Instead rectangular plots with varying length and width, and covering the whole cross section of riparian forest are the most suitable sampling units under the study area conditions, and probably for savanna regions too. The present study also provides scientific guidelines for an improvement of the forest law regarding the distance to be protected at riverside, and suggests 100 m instead of 25 m. In chapter 9 the floristic composition, species richness and structure of two riparian ecosystems in West Africa (the Comoé in Ivory Coast and the Ouémé in Benin ), are compared. The overall physiognomy of the two gallery forest sites seems similar and they share the most prominent families. However, there are marked differences in terms of canopy density and height, herb layer density, number of individuals, tree richness and diversity ( H' ), and species composition. The phenomenon of single species dominance at both sites is documented from Cynometra megalophylla , an evergreen tree species, which was time and again the most frequent and dominant tree at both riversides and in the middle of the gallery forests. Only detailed comparison shows the difference and complexity of ecological processes between and within gallery forests sites. The research carried out in chapter 10 facilitates the choice between several sampling designs for the estimation of a population parameter for endangered species. This study was carried out in the Pénéssoulou forest, in Central Benin . Stratified random sampling provided the lowest variance, coefficient of variation, standard error and sampling error. This method was taken as the most precise and reliable design over simple random and systematic samplings for the density estimation of Khayasenegalensis and K. grandifoliola trees. Results have confirmed empirical knowledge about the ecology of Khaya species and shown that the selection of the most precise sampling design, with regards to estimating a given parameter, can eventually be useful for the sustainable management of forest trees in the study area. A reliable density estimate for Khaya species within the given vegetation types facilitates the selection of areas to be protected and sustainably exploited. Chapter 11 presents a general discussion on issues discussed in this thesis. Sustainable rehabilitation and restoration of riparian forests biodiversity in Benin are discussed in the general conclusion ( chapter 12 ). This study has provided detailed site-specific data on plant species that can serve for further scientific research, as well as for conservation management and planning. It fills a gap of knowledge on the flora of Benin , and can contribute to better land-use planning and conservation of riparian forests.
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Thesis (doctoral)--Wageningen Universiteit, 2003. Vita. Includes bibliographical references (p. 167-189).
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