| Fundamental knowledge of biodiversity and how it is distributed in its natural occurrence plus the underlying processes that influence it are crucial to the study of an ecosystem and its conservation.However,the limitation of information impedes society's competence to find out the cause or significance of a problem or even to avoid further losses in an ecosystem.It becomes even harder to identify all the biological resources at risk because there is no exhaustive inventory of either fauna or flora of a particular region.Coastal forests of East Africa are considered as an exceptional biogeographical area with varied endemic flora and fauna and thus have been identified as one of the world's biodiversity hotspots.However,the distribution patterns of plant diversity around the region have remained obscure.Nonetheless,many studies have focused on species richness and conservation of rare and endemic animal species,but less attention has been paid to the conservation of the plant phylogenetic metrics.This study is aimed at:1)understanding both phylogenetic diversity of vascular plants of the coastal forests of East Africa,plant distribution along the latitude,the conservation status of endemic plant taxa;2)provide a comprehensive checklist,and distribution of endemic,threatened and near-threatened plant species found at the Kenya coastal region.A total of 32,922 specimen records from the coastal forests of East Africa,representing 5,056 species(including 717 endemics)belonging to 1284 genera and 199 families,were obtained from the Rain-bio database.This represents 22.39%,40.65%and 72.89%of species,genera,and families respectively found in tropical Africa.Plantlife forms found in the region were heterogeneously distributed from Northern to Southern parts of the region.Using phylogeny at genera level we calculated the phylogenetic diversity(PD)and standard effect size phylogenetic diversity(SES_PD).Consequently,we determined the latitudinal distribution of plant species and their life forms from north to the south region of East African coastal forests(00-250 S).Our results show that the phylogenetic diversity of the coastal forests of Eastern Africa is positively correlated with the species richness and most of the plots showed positive SES.PD meaning that species in these forests are distantly related hence having a high phylogenetic diversity.Plots with negative SES value could have been the ones that were located on the roads,farms since coastal forests are highly fragmented hence low phylogenetic diversity.Alternatively,this could be the area that have received little or even a few floristic studies.On the other hand,these regions could have experienced bias in the plant collections,whereby the collectors focus on a particular taxon and thus phylogenetic clustering.Plotting plant species richness of coastal forest of East Africa against the latitude was to test the well-known principle of the decline of species-richness along the latitudinal gradient.The results showed that plant richess increased with a decrease in latitude at the coastal forests of East Africa though low richness was recorded at around Somalia.Our results can be explained as the decline of species toward Mozambique is due to the principle that states that increase with the latitude species diversity decreases and species diversity increases with a decrease in latitude.Besides,the decline in species richness towards Mozambique could also be due to lower collection effort.Lower species richness recorded in Somalia might be caused by forest clearance according to Burgess et al.(2000),only 3 forest sites were thought to exist by 1986 and by 1994 only one fragment may be existing.However,plant sampling and digitization of herbarium specimen of the East Africa coastal remains poorly done.Conservation status of 717 endemic plant taxa belonging to 90 families and 320 genera documented in this study were evaluated,of these,312 taxa were assessed by IUCN Red list under criterion version 3.1 and 2.3 which represented 73%and 27%respectively.Taxa were represented as follows in each category:CR(39),EN(102),VU(104),NT(19),LC(40),and DD(8).With 39 endemic species recorded as Critically endangered(CR)and others possibly extinct this calls for an alarm to reevaluate some of the species evaluated under criterion version 2.3 and also for strict conservation measures to be put in place.Furthermore,these numbers record low compared to the number of endemic plant species recorded for eastern coastal forests and arc mountain in the previous studies,therefore digitization of plants of coastal forests of East Africa is highly recommended in addition to a more floristic expedition in the region.Additionally,a total of 2489 vascular species,100 infraspecific taxa(varieties and subspecies),90 endemic plant species,72 exotic species,and 120 species that are included in the current IUCN Red List of Threatened Species as species of major concern are comprehensively listed in this study.The list was compiled through numerous field investigations,checking herbarium specimen,obtaining data from published monographs or literature,and BRAHMS database.This represents 39.55%,63.78%,and 78.67%,of species,genera,and families respectively,of the total number of taxa found in the Kenyan flora.Also,the results represent more than half(51.20%)of the plant taxa found in the coastal forests of East Africa.4.8%of the total flora recorded for coastal forests of Kenya were threatened or near-threatened taxa with one species recorded as Extinct in the wild(EW)and 11 species as Critically Endangered(CR).Endemic species of Kenya's coastal region were unevenly distributed among the counties with Kwale county recording a high number of endemics and few species were noted to be site-specific.Furthermore,three new species to the world were discovered from Kenya coastal relicts,Adenia angulosa G.W.Hu&Q.F.Wang,Zehneria monocarpa G.W.Hu,V.M.Ngumbau&Q.F.Wang,and Croton kinondoensis G.W.Hu,V.M.Ngumbau&Q.F.Wang belonging to family Passifloraceae,Cucurbitaceae,and Euphorbiaceae respectively.The morphology of Croton kinondoensis and systematic position based on ITS and trnL-F DNA sequence data clearly places it within the Adenophorus Group of Croton,a clade of ca.15 species otherwise known only from Madagascar and the Comoros Archipelago.Its closest affinities appear to lie with Croton mayottae,from the island of Mayotte,and C.menabeensis,from northwestern Madagascar.This new species represents an independent dispersal of Croton from Madagascar to mainland Africa.Thus,Kenyan coastal forests present a remarkable and significant center of plant diversity and play an important role in the Flora of Kenya and the plant biodiversity of the coastal forests of East Africa for it harbors hundreds of plant species that are only found in the Eastern Africa coastal regions.Hence,this study provides not only a comprehensive list of the plant species that have been recorded in the coastal region of Kenya but also endemic species and species of special concern to guide conservationists and policymakers towards conserving the remaining forest patches.Also,it renders a solid basis for more sustainable management of rare,threatened and endemic species.In addition,it updates the plant biodiversity and document the species numbers found at the coastal forests of East Africa based on the data obtained from the Rain-bio database.Furthermore,this study is important because it achieves Objective 1 of the Global Strategy for Plant Conservation 2011-2020,which aims at documenting,recognizing,and understanding of plant diversity. |
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