An annotated checklist of the vascular flora of South and North Nandi Forests, Kenya

Abstract We compiled a checklist of the flora of South and North Nandi forests based on literature, online databases, herbarium collections and floristic field surveys. A combination of general walk-over surveys and plotless landscape sampling for plant collection and sight observation was used. We recorded 628 plant species representing 118 families and 392 genera, which almost double the latest results of the previous most recent survey. We found 61 species of ferns and fern allies and 567 species of seed plants, representing 9.98% of the total plant species in Kenya. Herbs were the majority (50.2%) of life forms followed by shrubs (16.5%). We report unique populations of three species out of 19 species that are widespread in Africa, but restricted to Nandi and Kakamega Forests in Kenya. Four of the recorded species are threatened globally and 16 exotic plant species were found. The recent description of one new species and two new records for Kenya from these forests, together with the comprehensive checklist is of crucial importance to the conservation of these unique ecosystems. Our results are essential to forest managers, community forest associations, conservationists, students and research scientists in Kenya and globally for implementing critical decisions for the conservation of this vital biodiversity resource.


Introduction
Tropical rainforests support more than half of the world's species (Armstrong 2016;McFarland 2018), although they constitute only 7% of Earth's land area. Nevertheless, no other land community sustains such a high species diversity and ecological complexity like tropical rainforests (Lewis 2006). As a result, they are very critical and essential in biodiversity conservation. Tropical forest ecosystems are crucial, because they act as reservoirs of biodiversity, they are sources of timber and medicinal plants, they also act as carbon sinks and play a critical role in watershed protection (Russo and Kitajima 2016;Maua et al. 2018a). Due to their diversity, tropical rainforests provide habitat for more than half of the world's known terrestrial plant and animal species (Lewis 2006;McFarland 2018). Globally, most forests experience enormous fragmentation as the human population increases; hence more land is needed to cater for human needs (Mitchell et al. 2006). Tropical forests are at the forefront of species extinction crises due to widespread habitat loss and alteration (Mwavu and Witkowski 2009;Vuyiya et al. 2014;Tanui 2015;Mutoko et al. 2015). Between 2000 and 2012, "the world has been losing about 0.43% of its remaining tropical rainforests per year (Lewis 2006;Mc-Farland 2018). Moreover, it is estimated that only 2.5% of the surface area of Earth is covered by rainforests, or approximately 8% of the land on Earth consists of rainforests (Pariona 2018). If this rate of loss persists, one-third of all remaining tropical rainforests will be primarily altered in the next 30 years (Althof 2005). Forests like North Nandi and South Nandi are diminishing due to the increased demand for their useful products and services (Mutoko et al. 2015). The tropical rainforests have received increasing attention both globally and locally due to their importance, with numerous efforts and calls for its proper assessment, management, conservation and documentation of their biodiversity status in a bid to prevent them from being wiped out.
Kenya has the most diverse forests in East Africa (Peltorinne 2004). They harbour over 6,000 species of higher plants, including 2,000 trees and shrubs (KIFICON 1994a;MEWNR 2015;Zhou et al. 2017). Although they are highly fragmented, these forests are biologically rich and harbour high concentrations of endemic species of animals and plants (Peltorinne 2004).
The Nandi Forests are within Nandi County in Western Kenya and occupy an area currently covered by three sub-counties, namely; Nandi Central, Nandi South and Kabiyet (Ehrich et al. 2007). They are enriched by Afromontane forest elements from the Rift Valley escarpment (Fischer et al. 2010). These two forests have been classified as semi-humid and as a nature reserve (Kigomo 1987). In the years from the 1980s and earlier, Kenya's indigenous forest coverage was about 2% (Wass 1995) and agricultural communities occupied most of the remaining areas. Some parts of the Nandi forests constitute a lowland rainforest-like Kakamega Tropical Rainforest (MEWNR 2015).
A careful review of the literature available for North Nandi and South Nandi Forests indicates that only a few floristic studies have been done in the past. Most plant species have not been fully documented and, if there is any documentation, it focuses on tree species (Koros et al. 2016). Previous research on these forests includes eth-nobotany studies, which recorded 56 plant species in 30 families that are useful in treating reproductive disorders (Pascaline et al. 2011). The list of tree species in North Nandi forest, used in the study by Diamond and Fayad (1979) while undertaking their Avifauna studies, had 56 species. An inventory by KIFCON (1994 a, b), that concentrated on the total standing volume of tree species, recorded 79 species in South Nandi and 65 species in North Nandi. A team from the National Museums of Kenya, who surveyed the biodiversity of these forests, recorded 125 plant species in South Nandi and 171 plant species in North Nandi (Musila et al. 2011). Finally, Maua et al. (2018a) found 128 plant species belonging to 105 genera and 55 families that are used as Non-Timber Forest Products (NTFPs) by households adjacent to South Nandi Forest.
The socioeconomic factors influencing the dependence of households on non-timber forest products in South Nandi Forest were addressed by Maua et al. (2018b). The most recent study about the floristic structure and plant composition in Nandi Forests (Girma et al. 2015) found 321 plant species in 92 families and 243 genera.
Other studies focused on the ecology, species distribution and composition, as well as the management of these forests by different stakeholders (Njunge and Mugo 2011;Mbuvi et al. 2015;Tanui 2015;Koros et al. 2016).
This study fills the existing knowledge gap by reporting on the indigenous flora of Nandi forests located near the remaining Kakamega Rainforest in Kenya. Our aim is to provide the first comprehensive, detailed checklist of the flora situated in this important biodiversity area to help in conservation and management, as well as determine the plant species composition and structure of North and South Nandi Forests of Kenya.

Study site and current vegetation status
Nandi Forests (Fig. 1) are situated on the top of Nandi escarpment in the Rift Valley Province of Kenya to the east of Kakamega Forest (KIFCON 1994a;1994b). It comprises of two forests; North Nandi to the north of Kapsabet town and measures about 10,501 ha (KIFCON 1994b) and it stretches for more than 30 km from north to south. It is seldom more than 5 km wide or less than 3 km wide for a considerable part of its length (KIFCON 1994b) while South Nandi Forest is situated to the south of North Nandi Forest and covers 19,502 ha (KIFCON 1994a). North Nandi Forest, together with the Kakamega Forest and South Nandi Forest, is one of the three forests in western Kenya, southeast of Mount Elgon (Schifter et al. 1998). North Nandi forest is found in Nandi North District between 00°12.38'-00°25.10'N latitude and 34°57.58'-35°01.05'E longitude. South Nandi Forest is situated in Nandi South District between latitude 00°34'N and 35°25'E (Maua et al. 2018b). The elevation of Nandi Forests is between 1695 and 2145 m. The mean annual rainfall is 1800 to 2000 mm, with peaks in April/May and August/September. (Mitchell et al. 2006;Lung and Schaab 2010;Maua et al. 2018b).
The mean annual temperature ranges between 17 °C and 20 °C, with the mean maximum and minimum of 25 °C and 11 °C, respectively (KIFCON 1994a). The soils of the North Nandi Forest are derived from undifferentiated basement system rocks and are well-drained, deep and red to yellowish-red friable sandy clays (KIFCON 1994a (Girma et al. 2015;KIFCON 1994a).

Floristic surveys, specimen collection and identification
Floristic surveys and specimen collections were conducted between November 2016 and April 2019. The botanical team consisted of botanists from the National Museums of Kenya and the Sino-Africa Joint Research Center (SAJOREC). Our study covered the entire forest from 40 sites within the two forests, 20 in South Nandi and 20 in North Nandi Forest. A combination of general walk-over survey method (Filgueiras et al. 1994) and a plotless landscape defined sampling methods for plant specimen collection and sight observation was used to aid the characterisation of the vegetation (Hall and Swaine 1981). Plant specimens bearing flowers or fruit were collected and identified. The habit, habitat, elevation and collector details were recorded. The samples were then preserved by pressing. All the plant specimens collected are stored at the East Africa Herbarium (EA) and Wuhan Botanical Garden (HIB).
All vascular plant specimens, that were previously collected from the entire former Nandi District and particularly North and South Nandi Forests, were compiled from 43 herbarium specimens in the East Africa Herbarium at the National Museums of Kenya. Additionally, the species collected in the previous decades are reported in this checklist. These were obtained by searching the locality "Nandi District" records in literature (FTEA 1952-2012, Beentje et al. 1994, Agnew and Agnew 1994Agnew 2013). These botanical references were also used to identify the specimens that we collected. The state of endemism was evaluated by searching all the vascular plants recorded, including existing endemics cited in literature in the Global Biodiversity Information Facility (GBIF) (www.gbif.org). The conservation status of all the vascular plant species collected was assessed using the criteria from the International Union for Conservation of Nature (IUCN 2019) (https://www.iucnredlist.org/).
Habitat description for each species was based on our field observations. For those species that we collected more than one specimen, maximum and minimum altitude ranges are recorded in the checklist. For the herbarium specimens, their habitats were not restricted to the Nandi Forests, since some of the species had wide distribution ranges. The life form information was obtained from field observations and botanical literature. They were categorised as trees (main trunk over 3 m tall, shrubs (0.5-3 m plants with woody stems branching near the ground), climbers (with twinning herbaceous or woody stems) and herbs (< 0.5 m, or < 1 m without persistent woody stems).

Checklist
A comprehensive checklist of the vascular plant taxa of the Nandi Forests is enumerated below. Families are grouped in lycophytes, monilophytes, gymnosperms and angiosperms. Families in lycophytes and monilophytes follow the PPG I system (PPG I 2016), those in gymnosperms are based on Christenhusz et al. (2011) and families in angiosperms are based on the APG IV system (Chase et al. 2016). Recently-described species and new floristic records for Kenya are indicated in the checklist. Asterisk (*) before the name indicates the introduced species. The conservation status of vulnerable taxa is shown at the end of the taxon.

Families, genera and species diversity
The current list contains 628 vascular plant taxa representing 118 families and 392 genera. Out of the total species recorded, 43 species were obtained from herbarium specimens at the National Museums of Kenya. Lycophytes and monilophytes comprised 61 species. Seed plants included 567 species, representing 9.98% of the 6,293 total vascular plant species in Kenya recorded by the Flora of Tropical East Africa. Angiosperms represent 90.12% of the total species collected in Nandi Forests (357 genera, 566 species), followed by monilophytes with 9.4% (33 genera, 59 species), lycophytes with 0.3% (1 genus, 2 species) and gymnosperms with 0.2% (1 genus, 1 species).

Plants life forms
The majority of the plants were herbs comprising 50.2% of the total plant species, followed by shrubs, trees, climbers, epiphytes, shrubs or small trees, lianas and subshrubs (Table 2).

Plant species of special concern
Exotic species We recorded 16 introduced or exotic plant species (3.02%) belonging to 13 genera and eight families (Table 3). These plants represented 2.5% of the total plants collected in Nandi Forests. The families with more species were Fabaceae (4), Asteraceae (3) and Solanaceae (3). All these plants originated from eight different regions (Table 3). Most of the introduced species were from South America (7), Central and South America (2) ( Table 3).

Widespread taxa restricted in Kenya to Nandi and Kakamega Forests
The checklist contains 19 species that are widespread in Africa but are restricted in Kenya to the Kakamega and Nandi Forests (

Discussion
The present checklist provides a comprehensive inventory of the vascular plants found in North and South Nandi forests. Our list almost doubles the previous floristic account by Girma et al. (2015) where 321 plant species in 92 families and 243 genera were recorded.
Most of the species in our checklist are present in the adjacent Kakamega rainforest (Fischer et al. 2010). This could be because in the early 20th century, Kakamega, North and South Nandi forests were once joined, forming a u-shaped forest block (Kigomo 1987;Mitchell et al. 2006;Lung and Schaab 2010). That forest block is currently divided into three different areas, namely Kakamega, North Nandi and South Nandi forests. Nandi forests play an essential role in the endeavour of conserving the Kakamega forest and they are environmentally significant as they protect the catchment of Nandi escarpment and the Lake Victoria basin.
South Nandi and North Nandi forests contain highland elements in its fauna and flora and are thus unique (Girma et al. 2015). Moreover, together with Kakamega forest, the North Nandi forest and South Nandi forest form part of the western rainforest region and the easternmost fragment of the Guinea-Congolian phytogeographical region (Mbuvi et al. 2015). The high number of threatened species in these forests indicates their importance as a global biodiversity resource (MEWNR 2015).
These forests are surrounded by many people who depend on them entirely or partially for their ecosystem services like timber, firewood, pasture, charcoal, medicinal plants for people and livestock and building materials, amongst many other functions (Fashing and Mwangi 2004;Akwee et al. 2010;Maua et al. 2018b).
Currently, this region is amongst the most densely populated rural areas in Kenya (Mitchell et al. 2006). The demand pressure on the limited resources of North and South Nandi forests is high (Kogo et al. 2019). Therefore, efforts to manage and conserve the forest's resources in a sustainable way will be crucial to the survival of this vulnerable ecosystem (Bennun and Njoroge 1999;Matiru 2002).

Conclusion
The description of one new species and two new records for Kenya from Nandi forests, together with this comprehensive checklist, is a clear indication that opportunities for scientific studies are abundant in North Nandi and South Nandi Forests and are of crucial importance to the conservation of these unique ecosystems. Other than this checklist, very little is known about the specifics of the community or ecosystem ecology of North and South Nandi Forests. Hence, more studies should be done in this area to fill the existing knowledge gaps.