Browsing by Author "Njiru, Derrick Muthomi"

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    Geomorphic and Climatic Drivers Are Key Determinants of Structural Variability of Mangrove Forests along the Kenyan Coast
    (MDPI, 2022-06) Njiru, Derrick Muthomi; Githaiga, Michael Njoroge; Nyaga, Justine Muhoro; Lang’at, Kipkorir Sigi; Kairo, James Gitundu
    Mangrove forests occur across a diversity of coastal landforms that influence their structural development and productivity. Preliminary studies in Kenya indicate that mangroves growing in the region north and south of Tana River delta have different structural attributes. We hypothesise a close relationship between mangrove distribution, climate and landform types. Floristic composition of mangroves along the coast of Kenya was characterised and differences illustrated using non-metric multidimensional scaling (nMDS). Other structural properties of mangroves such as tree height, basal area, stand density and standing biomass were also assessed and their differences tested using analysis of variance (ANOVA). A hierarchical cluster analysis was used to compare mangrove species based on structural properties. Additionally, a regression fit model was used to investigate the relationship between mangrove standing biomass and possible drivers of variability. The study revealed significant differences in mangrove tree diameter, tree height, basal area, stand density and standing biomass across the sampled sites. High values of structural complexity were observed in estuarine and deltaic settings with high influence of freshwater input whereas low levels of structural complexity were observed for peri-urban with direct human influence. Our findings suggest that structural variability of mangroves in Kenya is highly influenced by geomorphological and climatic variability along the coast as well as the past and present management regimes of the forest.
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    Structural Variability Of Mangrove Forests along the Coast of Kenya
    (UoEm, 2023-08) Njiru, Derrick Muthomi
    Mangrove forests occur across a diversity of coastal landforms with different geomorphological, climatic and oceanographic influences. These factors influence mangrove structural development and productivity and as a result, the structural development of mangroves varies with the coastal geomorphology. Earlier inventory studies in Kenya suggest that mangroves growing in north of the Tana River have different structural attributes from those growing south of the river. The current study characterised the structure and floristic composition of mangroves in Kenya by describing species composition, basal area (m2 ha-1), stem density (trees ha-1), importance value index complexity index and above ground biomass (Mg ha-1) across 14 sites spread across the coastline of Kenya. Variability in mangrove floristic composition was tested using analysis of similarities (ANOSIM) and the differences illustrated using non-metric multidimensional scaling (nMDS). Mangrove structural variability was tested using analysis of variance (ANOVA) and comparisons made by performing a post-hoc Tukey pairwise test. A hierarchical cluster analysis was then performed to determine the degree of similarity in mangrove species across the sites based on complexity index, biomass, tree diameter and tree height. To investigate the relationship between mangrove structure and possible drivers of variability, a regression fit model was used. The model described associations between mangrove standing biomass, environmental settings, precipitation, population density, and riverine influence across the sampled sites. Rhizophora mucronata was the most important species in most of the sites while Avicennia marina was the most important species in the estuarine area of Ungwana Bay. High values of structural complexity were observed in the estuarine and deltaic settings of Ngomeni and Kipini while relatively low levels of structural complexity were observed for the periurban mangroves of Mombasa and Mtwapa. Mangrove forest species composition differed significantly across the sampled sites (ANOSIM R: 0.24, p = 0.001). The mangroves of Kipini were significantly different from the rest of the sites. The study revealed significant differences in structural attributes of mangroves growing along the coast of Kenya, specifically, tree diameter [F (13, 34050) =163.01, p=0.000], tree height [F (13, 34050) =1827.28, p=0.000], basal area [F (13, 358) =5.45, p=0.000)], stand density [F (13, 358) =8.68, p=0.000], and standing biomass [F (13, 358) =15.36, p=0.000] across the sampled sites. Environmental settings and population density best explained the variability in mangrove standing biomass. The study suggests that the patterns of mangrove structural variability in Kenya closely follows the patterns of geomorphic variability along the coast. The study concluded that mangroves in Kenya are highly influenced by geomorphological and climatic variability along the coast as well as human influences. These findings are useful for mangrove managers and policy makers and have the potential to guide strategies and actions aimed towards sustainable management of mangrove forests in Kenya.