Flora And Diversity Of Vascular Plants In Taita Hills,Kenya

Tropical forests are one of the most inhabited ecoregions in the world.They are also very rich in biodiversity and harbor nearly half of the total world's known plant species.Due to the conducive climate and reliable weather patterns in these areas,they are suitable for intensive farming.This has led to the clearance of most tropical forests to pave way for agriculture as well as to provide timber and timber products.Many of the tropical forests are highly fragmented and thus range-restricted taxa in these forests are facing extinction threats,making these forests the most important ecosystems in need of priority conservation.The Eastern arc mountains(EAM)of Kenya and Tanzania are ranked among the priority biodiversity hotspots in the world due to the high concentration of narrow distribution of endemic and threatened species making the region one of the world's 36 biodiversity hotspots.Taita hills cloud forests cover the smallest geographical area compared to other forests in the EAM and are the most degraded in this hotspot having lost 98% of their original habitat.Despite their degradation and fragmentation,these forests exhibit high species diversity and endemism per area covered.There have been periodic botanical explorations in the region since 1877 but many of these have resulted in herbarium specimen without any publications.Also,for the expeditions that were documented,only a section of the flora was published.Therefore,species diversity within these Afromontane forests remained unknown as the forest continued to be endangered due to population pressures and encroachment.In this study,we aimed at understanding the plant diversity of vascular plants in the Taita Hills indigenous forests as well as the bushland and woodland vegetation along the slopes.We also sought to record endemic and near-endemic species,the conservation status of species collected,and exotic species that occur within these forests.Field investigations were carried out between November 2015 and April 2019 during different seasons.Using the general walk-over survey method,we collected fertile specimens in quadruplets,identified,pressed and deposited them in EA and HIB herbariums.To supplement our records,herbarium species from the EA herbarium were recorded as well as digitized specimens from other online databases.We recorded 1659 taxa(1583 species,354 infraspecific taxa,and 2 hybrids)representing717 genera and 165 families of vascular plants within the Taita Hills.These represent 26.25%,46.63%,and 73.33% of all the families,genera,and species in the flora of Kenya.The most species-rich families were Fabaceae(127 species),Rubiaceae(80 species),Asteraceae(79species),Orchidaceae(73 species),and Apocynaceae(66 species).A total of 76 endemic and near endemic plant species,47 exotic species,and 83 species that are included in the current IUCN Red List of Threatened Species as threatened or near-threatened are comprehensively listed in this study.Endemic species of Taita hills were unevenly distributed among the forest fragments with the Ngangao fragment recording the high number of endemics.Plant life forms in Taita Hills were categorized either as trees,shrubs,subshrubs,lianas,climbers,and herbs.Herbs comprising 40% of the total species were the most abundant life form.Of these,32 % were terrestrial herbs while 8% were epiphytic.For the threatened and nearthreatened species,trees were the highest in number representing 37.35%.In terms of exotic taxa,herbs were the most speciose life form,making up 40.81% of the total.Overall,most life forms were abundant in the forest and bushland habitats which represented 55% of all habitat categories.The distribution of plant forms of vascular plant species recorded in Taita Hills varied from one habitat to another.Herbs were in general most abundant in all other habitats with an exception of the bushlands and woodlands.The distribution of species along the altitude gradient was highest between 900–1000 m and 1500–1600 m while there was a decline between 1000–1300 m and 1901–2300 m due to deforestation,small land area on the hill-tops,and heavy forest disturbances.Plant species recorded in Taita Hills varied in terms of their geographical distribution range.The majority of the species,79.83% of the total taxa recorded,were distributed widely in Africa and the world.Species with a wide distribution range represented 158 families and 663 genera.The most speciose families in this category were Fabaceae(116 taxa),Asteraceae(58 taxa),and Apocynaceae(48 taxa),while the most speciose genera are Asplenium(29 taxa),Plectranthus(23 taxa),and Euphorbia(17 taxa).Species that had their range of occurrence restricted to Kenya and East Africa made up 18.60% of the total taxa and represented 72 families and 178 genera.In this category Rubiaceae(36 taxa),Fabaceae(24 taxa)and Euphorbiaceae(20 taxa)were the largest,while the genera Euphorbia(16 taxa),Aloe,Commiphora,Cyphostemma,and Ipomoea(7 taxa each)had the highest number of species.Only 17 species representing 11 families and 14 genera were restricted to Taita Hills.Rubiaceae had the highest number of taxa(four)while nine families had only one species.For the 47 exotic species recorded,23 families and 42 genera were represented with Asteraceae,Fabaceae,and Solanaceae having the most taxa(6 each)while Solanum was the most speciose genera(3 taxa).In addition,a new species Zehneria tuberifera G.W.Hu & Q.F.Wang belonging to the family Cucurbitaceae was discovered from the Ngangao fragment of Taita hills.A new record,Momordica calantha Gilg,also from the same family,was recorded for the first time in Taita Hills from the highly degraded Wusi fragment.The Taita Hills forests are still under constant threat of encroachment.Only three of the 14 indigenous fragments are gazetted and therefore there is no clear demarcation of the forest boundaries.The comprehensive listing of endemic and threatened species in this study will serve as a guideline to enable policy-makers to make more informed decisions and appropriate strategies in the conservation and management of biodiversity in the area.It also sets a foundation for other floral studies in these forests and updates the plant biodiversity records of the Taita hills ranges.