The study site is located within the Chemeron Dryland Research Training and Ecotourism Centre (Figure 1), which is approximately 120 km northwest of Nakuru town. It is approximately 11 km from Marigat town, and 2 km off the Marigat-Kabarnet road, in Baringo County. It is located within Agro-Ecological Zone V and receives an annual rainfall of about 635 mm annually. The rainfall is less than 30% reliable with high variability. The long rains fall in the months of April to July whereas the short rains fall between end of September and early November. The driest months occur between January to March. The altitude at

the study area is approximately 1200 m above sea level. The temperature ranges from 25˚C to 38˚C. The soils are reddish brown, sandy loam with many rocky outcrops that makes it unsuitable for the growth of many of the commercial food crops in Kenya (e.g. Maize, wheat, tea, coffee, etc.). The ground has a gentle slope and drains into the Chemeron River, a seasonal river that drains into Lake Baringo via the Perkerra River.

The vegetation of the area is mainly dominated by different species of acacia, among them Acacia mellifera, Acacia tortilis, Acacia reficiens, Acacia brevispica and Acacia senegal. Other trees and shrubs in the study area include: Boscia anguistifolia, Balanites aegyptiaca, Grewia bicolor, Terminalia brownii, Maerua angolensis, Acalypha fruticosa and Berchemia discolour. The main grass species in the area include Aristida keniensis, Chloris roxburghiana and Eragrostis superba. The soils are not well developed and thus the prevalence of agro pastoralism characterized by beekeeping and livestock production involving goats and cattle as the preferred animal species. The growing of commercial crops is inhibited by the dry, rocky and shallow sandy soil conditions. The area is suitable for the cultivation of drought tolerant crops including finger and pearl millet, pigeon peas, vegetables and fruit crops such as mangoes, pawpaws and lemons.

Of the 1100 acres of land belonging to the Chemeron DRTEC, approximately 60 acres of it has been fenced off and livestock excluded from the area, whereas the rest constitutes the grazing fields for goats and cattle. Acalypha fruticosa was removed by uprooting from the enclosed area in 2013/2014 and natural restoration took place over the years.

To achieve the objectives of this study, two sites with contrasting features (enclosed and open sites) were selected for this study. First, an area devoid of interference from livestock through grazing was selected. This site was within the 60-acre fenced area at the Chemeron DRTEC while the other site was in the open grazing fields. The transects within the enclosed area are herein labelled as AFA-A & AFA-B corresponding with Transect A and Transect B without Acalypha fruticosa, respectively. The transects within the open grazing area are herein labelled as AFP-A & AFP-B corresponding with Transect A and Transect B with Acalypha fruticosa, respectively. The main plant species in the area included Indigofera arrecta, Silene spp., Microchloa kunthi, Aristida keniensis, etc. The enclosed area was kept A. fruticosa—free through regular uprooting of the invasive shrub. The Transect and Quadrat Technique (TAQ) was used in the study of plant composition, relative abundance and diversity. Four transects (two within an enclosed area (Acalypha fruticosa absent, AFA), and two in an adjacent open area (Acalypha fruticosa present, AFP) measuring 100 m by 20 m were selected for this study. Samples of different plant life forms (herbs, grasses) were collected from quadrats measuring 1 m × 1 m laid systematically at intervals of 20 m in both the enclosed and open areas (Figure 2). Shrubs and trees were sampled using 5 m × 5 m quadrats. Data was analyzed by use of Species Richness Index (D) [13] and diversity assessed using Shannon-Weiner diversity index (H) [14].

H = ∑ ( p l ) | ln p l | (1)

where pi is the proportion of the total number of individuals in the sample that are in species i.

Species richness was calculated using the equation below:

Maximum number of species, H max = ln ( S ) (2)

S is the total number of species in the samples

D = S / N (3)

where S is the number of different species in the sample.

N is the total number of individuals in the sample

Evenness was calculated as H / H max (4)

References to the equations and protocols used in this study are as described in Shannon & Weiner [14], Magurran [13], and Ibrahim [1].

In each plot, all species of plants were recorded and documented in terms of family, form, species, and uses. Determination of plant species abundance and diversity was done as per protocols describe in Ibrahim [1] and Magurran [13]. The effects of the invasive species (Acalypha fruticosa) were determined through comparison of differences in species richness, S, Shannon-Wiener index and evenness in the two study sites. Species distribution in the study site was determined through observation of how different plant species were evenly spread in a transect. Species diversity takes into account both the numbers of species present and the dominance or evenness of species in relation to one another. Whereas several plant diversity indices were calculated, the Shannon-Wiener diversity index was the best suited to measure the species diversity in the study sites as it is fairly sensitive to site differences. The invasive species was excluded from the calculation of community characteristics.

The plant survey yielded a total of 47 species of which 37 of them occurred in the sites where Acalypha fruticosa had been removed (AFA). Only 20 plant species were collected from the transects in the site with present Acalypha fruticosa (AFP). Thus variations in species composition between the two study sites were noted (Figure 3). The plants constituted annuals (e.g. Aristida keniensis, Tribulus cestoides, Oxygonium sinuatum) and perennials (e.g. Aeva persica, Indigofera arrecta, Acacia species, and Acalypha fruticosa). Our results indicated that the removal of Acalypha fruticosa (copper leaf) significantly increased species

abundance and diversity (Figure 5; Table 1). The dominant plant species in the AFA sites included: Indigofera arrecta, Silene species, Microchloa kunthi, Aloe graminicola, and Ocimum Mexicana (Figure 3). In the AFP sites, the dominant species were Indigofera arrecta, Acalypha fruticosa, Microchloa kunthii, and Acacia senegal (Figure 3). Approximately 47% of the plants in the survey were shrubs whereas the lowest were trees at 11% (Figure 4). The dominant plant species among the shrubs was Indigofera arrecta. More than 80% of the grasses enumerated during the survey occurred in the site where Acalypha fruticosa had been removed.

Various indices including Shannon-Wiener (H’), Evenness Index, Richness Index and Simpson’s Index of Diversity Index (SDI) were calculated. All the indices were considerably higher in the site without A. fruticosa compared to that where this invasive species was present (Figure 5). Significant differences were also observed in the Shannon-Wiener Index (t = 12.75; p = 0.025), Evenness Index (t = 5.88; p = 0.04) and species richness (t = 26.87; p = 0.001). However, no significant differences were observed in the Simpson’s Diversity Index (t = 3.35; p = 0.18).

Diversity in range plant community has several benefits, among them being that a mixture of plants provide forage for a variety of insects and vertebrate species. This will therefore enhance biodiversity in the rangeland. Having a mixture of plants will mean that some of the plants may survive drought, insect plagues and disease outbreaks in the event of occurrence. Therefore, the rangeland will have some soil protection as well as fodder in such periods. A mixture of plants in the rangeland is also beneficial in that some of the plants may be nitrogen fixers hence improving soil conditions, some may be deep rooted thereby bringing nutrients

on the surface. Lastly, these plants may also be functioning together (commensalism) to ensure that both can survive in any given weather conditions. Invasive

plant species in Sub-Saharan Africa represent a potential agent of environmental degradation [15] through loss of biodiversity that is a major threat to the conservation and sustainable use of drylands [16]. Our findings are consistent with those of [17] that showed that invasive species can lead to a reduction in resource availability and/or suppress or enhance the relative abundance of the native plant species. Mangold et al. [3] observed that invasive plants are a threat to the integrity of rangelands and that they may alter the structure, organization, and function of rangeland plant communities. As noted in this study of the impact of Acalypha fruticosa, invasive species are considered a major threat to biological diversity and likely to displace native plants [3].

Species evenness refers to how close in numbers each species in an environment is. The higher the value, the more the richness. From the results obtained in the two sites, the A. fruticosa-absent site is richer in species than those where it is present. To measure species richness, we used the Simpson’s diversity index. The bigger the Simpson’s index value, the lower the diversity. Thus species richness was higher in areas where Acalypha fruticosa has been removed, suggesting the negative effects that the shrub has on other plant species in the rangeland. Enclosures and removal of invasive species have been used effectively within the rangelands as a resilience mechanism against drought to secure livelihoods in the ASALs of Kenya [15]. Further, they have been used to protect selected areas from overgrazing and enhance forage availability and curb degradation of these fragile ecosystems. Our findings are consistent with those of Wu et al. [18] that indicate that enclosures have a considerable positive influence on community structure and productivity, and thus strongly recommended as a management tool for rangelands conservation. Enclosures have also been shown to preserve some of the most important life forms (e.g. grasses and herbs) in rangelands that constitute livestock fodder leading to an increase in vegetation density, reduction in soil erosion, and increased forage availability [15].

Our study demonstrated a positive effect of the mechanical removal of Acalypha fruticosa on plant species diversity and abundance. These results are consistent with those of Ibrahim [1] that demonstrated the positive impact of enclosures on plant species composition in the rangelands of Ethiopia. Further, Crawley & Del-Val [19] noted an increase in desirable or palatable grass species in enclosures compared to open grazing fields. Similar observations have been reported by Ibrahim [1] who further argues that enclosures are effective in restoring plant species composition, biomass and cover of herbaceous species. In the current study, the number of palatable grass species in the sites where Acalypha fruticosa had been removed was considerably higher than those with the invasive plant present. This observation is similar to that made by Ibrahim [1] that linked diminished plant species composition in open grazing fields to communal grazing and other inappropriate and unsustainable range utilization practices.

Acalypha fruticosa had minimal effects on Silene spp and Indigofera arrecta whose abundance in both sites (with and without A. fruticosa) was similar. The two species contributed greatly to the relative of figures observed in both sites. Decrease in species evenness and diversity is mostly driven by the cover and height of the copper leaf. The impact of the invasive species is normally associated with the degree of its dominance [20] [21] [22]. In our study, the more copper leaf present in a particular area, the lower the number of native species and thus reduced species diversity.