Spatial variation of population size structure of selected riparian tree species in the Okavango Delta, Botswana

Tsheboeng, Gaolathe; Murray-Hudson, Michael

doi:10.7809/b-e.00287

Cited by 10 publications

(6 citation statements)

References 30 publications

(16 reference statements)

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“…Other "disturbing factors" include erosion and sediment deposition, and actions by biological engineers like elephants, hippos and termites (Mosepele et al, 2009). Frequent disturbances in the Delta create small-scale habitat patches, which facilitate the co-existence of different successional stages of plant communities (Tsheboeng and Murray-Hudson, 2013). Generally, flood pulsed systems provide diverse food items to food webs, and act as dry season refuges for migrating mammals (Junk et al, 1989;Junk et al, 2006;Bartlaam-Brooks et al, 2011).…”

Section: Flooding Dynamics In the Deltamentioning

confidence: 99%

The Okavango Delta: Fisheries in a fluctuating floodplain system

Mosepele

Kolding

Bokhutlo

et al. 2022

Front. Environ. Sci.

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Wetlands are among the most productive ecosystems globally characterized by dynamic interactions between terrestrial and aquatic habitats at different scales. These systems support valuable floodplain fisheries that are a major livelihood for riparian communities. Understanding the dynamics of these systems is important for developing adaptive fisheries management paradigms that will facilitate access and sustainability to this cheap but high-quality food and nutrition source. The Okavango Delta in Botswana is a large land-locked complex river-floodplain ecosystem, with a diverse biota, and high environmental heterogeneity due to periodic drying and flooding along a space and time gradient. It is characterized by a multi-species, multi-gear fishery adapted to the seasonal flood pulse. The Delta’s fish species assemblage undergoes seasonal changes driven by the flood regime. There is also a dynamic inter-annual variability in the fish species assemblage, particularly between “good” and “bad” flood years. During the wet season, high flows increase connectivity in three dimensions (longitudinal, lateral, and vertical) which facilitates dispersal of aquatic biota, nutrients, and other material among successive locations in the riverscape. However, the dry season results in alteration or reduction in aquatic habitats available for fish reproduction. Similarly, low floods may reduce inputs of nutrient resources from the terrestrial environment that support aquatic food webs and can lead to community disruption, even to the point of local extirpation of stranded fish in fragmented ephemeral pools in the floodplain. Consequently, the periodicity, magnitude and predictability of flows are the major drivers of the systems’ capacity to sustain persistent fisheries production and other ecosystem services affecting human welfare. We argue that identification of the processes that sustain production and biodiversity patterns is an essential step towards a better ecological understanding and natural resource management of river-floodplain systems. Based on this review, we debate that floodplain fisheries, like in the Okavango Delta, should be exploited using a diverse exploitation pattern to ensure a harvesting regime in balance with system productivity. Such balanced fishing pattern, based on traditional fishing practices, facilitates the provision of food and nutritional value of the fishery to marginalized communities.

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Section: Flooding Dynamics In the Deltamentioning

confidence: 99%

The Okavango Delta: Fisheries in a fluctuating floodplain system

Mosepele

Kolding

Bokhutlo

et al. 2022

Front. Environ. Sci.

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“…Philonoptera violacea (Figs z,c) showed a conspicuous ‘sapling gap’ but an abundance of small individuals and adults, indicating a failure of sapling recruitment from regeneration that, if maintained, would lead to population decline. A similar structure was evident for this species in the Okavango, Botswana (Tsheboeng & Murray‐Hudson ), as well as for S. birrea at one location in the Kruger National Park (Helm & Witkowski ), the cause of which was not revealed. This riparian species is largely ignored by elephants but its main future threat is continuing attenuation of river flow (O'Connor ).…”

Section: Discussionmentioning

confidence: 60%

Population size structure of trees in a semi‐arid African savanna: Species differ in vulnerability to a changing environment and reintroduction of elephants

O’Connor

Goodall

2017

Austral Ecology

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The size structure of a plant population provides a snapshot of potential population trend and weak inference on past history. Size structure of 24 tree species was sampled in a savanna reserve in order to assess their potential vulnerability to local extirpation following the reintroduction of elephants. Regression of number per size class based on an expected reverse-J structure for a healthy population was undertaken in order to classify trend of each species. On account of the weak realism of this expected structure in semi-arid environments, log-normal mixture models were also fitted to individual observations in order to identify states, whose distribution, size and shape can indicate potential population persistence. Population structure of 12 species approximated a reverse-J, indicating potential future growth. Although regressions of seven species were not significant, suggesting vulnerable populations, mixture models of all except one showed multiple states, indicating variable regeneration and recruitment over time. A single state of adult plants indicates that Sclerocarya birrea was vulnerable to local extirpation if adult mortality escalates. Some apparently declining populations displayed multiple states of established individuals suggesting temporally varying regeneration and recruitment, attributed mainly to rainfall variation, but which were judged as likely to persist. Poor recent regeneration of most species was attributed to well below-average rainfall for the preceding decade. Different savanna tree species apparently ensure persistence based on individualistic responses to population perturbations, but persistence of some following the reintroduction of elephants may be threatened if certain size classes experience escalated mortality. Subsequent monitoring has supported this concern.

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“…The occurrence of flooding either seasonally or permanently in most of the studied sites might have contributed to the dominance of some families recorded in the vegetation of the riparian sites in southwestern Nigeria. Higher richness of Rubiaceae and Fabaceae have been reported to be related to high flooding frequency and symbiotic dinitrogen fixation respectively which have significantly improved their adaptation to the wetland ecosystems (Koponen et al 2004, Sambare et al 2011, Tsheboeng 2016). The dominance of Apocyanceae by lianas in this study may be related to various anthropogenic activities taking place at the various study sites as reflected in the land use change (Borisade et al 2021).…”

Section: Discussionmentioning

confidence: 99%

Floristic composition, structure and diversity of riparian forests in southwestern Nigeria: conservation is inevitable

Borisade¹,

Odiwe

2023

Nordic Journal of Botany

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The Nigerian riparian forest ecosystems had declined in extent and distribution and this had been attributed mainly to land use change. This study intended to provide understanding links between plant diversity, composition, structures and disturbances both anthropogenic and natural processes inducing the vegetation dynamics. Nine study sites were used for this study, within each site, five (5) plots (0.25 ha in size) were marked out, placed systematically at an interval of 10 m along transect. Complete enumeration of plants species was carried out and identified to species level. Diversity indices and structural parameters were determined and anthropogenic activities were ranked. A total number of 233 plant species were identified, belonging to 80 families; out of which, Euphorbiaceae and Apocynaceae were dominant families. The density and basal area ranged from 2200 to 6000 ha −1 and 2.59 to 17.58 m 2 ha −1 respectively across the study sites. Pterocarpus santalinoides, Alchornea cordiflora, Chassalia kolly, Tetracera spp., Fimbristylis, Bambusa vulgaris and Cyrtosperma senegalense were the dominant species. The Shannon diversity index ranged from (1.38-3.49), Simpson (0.66-0.97) and Evenness diversity was (0.43-0.84). Fisher alpha (10.03-30.21) and Whittaker beta diversity (0.36-0.89) values were highest in Ipetumodu (site VIII) and lowest in Ilesha (site II). Seventy-three (73%) of the species in this study had low important value index (IVI). The dominance of some lianas and herbaceous species in the riparian forest sites showed disturbances, stages of ecological succession and regeneration of the vegetation. Conservation is inevitable towards maintaining and protection of species diversity, ecosystem roles and services of these forests in Nigeria.

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Spatial variation of population size structure of selected riparian tree species in the Okavango Delta, Botswana

Cited by 10 publications

References 30 publications

The Okavango Delta: Fisheries in a fluctuating floodplain system

The Okavango Delta: Fisheries in a fluctuating floodplain system

Population size structure of trees in a semi‐arid African savanna: Species differ in vulnerability to a changing environment and reintroduction of elephants

Floristic composition, structure and diversity of riparian forests in southwestern Nigeria: conservation is inevitable

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