Short-Term Effect of Grazing Exclusion and Uncontrolled Grazing on Species Abundance, Dry Matter Yield and Nutritive Value in an Invaded Area by Euryops floribundus in the Eastern Cape, South Africa

Grazing exclusion (GE) is the most effective rangeland restoration technique which facilitates species diversity and forage quality. This study aimed at assessing short-term impact of GE and continuously grazed rangeland on relative frequency, dry matter yield and nutritive value of dominant grasses in an area invaded by Euryops floribundus. A plot of 2.5 ha was measured and the boundaries demarcated using tape measure and steal pins, the plot was further divided into two subplots of 1ha each which were 5 m apart. One subplot was fenced and protected from grazing livestock, while one subplot was grazed continuously and not fenced. Three parallel belt transects of


Introduction
Grassland biome covers approximately 40% of the earth's surface [1] [2]. Exploitation of grassland resources have become a major concern towards achieving United Nations' Sustainable Development Goals [2]. Gradual deterioration or depletion of grazing resources through overgrazing and spread of undesirable plants were the most reported constraints hindering food security and livelihoods of communal farmers [3] [4]. According to [5], rangeland deterioration is associated with socio-cultural behaviour (anthropogenic activities) environmental factors and ecological processes such as the interaction between species communities and seed dispersal.
Eastern Cape Province in South Africa is not an exception, invasion of Euryops floribundus has been reported as a primary threat on the sustainability of livestock production and livelihood of communal farmers [6] [7] [8]. The grazing management system employed and spread of Euryops floribundus in the communal areas have changed native forage quality, nutritive value of herbaceous species, the hydrology and soil properties leading to land degradation [6] [8] [9]. [2] indicated that rangeland conservation is vital for sustainable livestock production in harmony with the United Nations' Sustainable Development Goals. For restoration of rangelands, grazing exclusion is one the rangeland management practices which influences species diversity, forage quality and quantity [5]. Grazing systems such as the continuous or rotational grazing have a great impact on vegetation communities influencing forage quality and quantity. Hence, knowledge on the dynamics of forage quality and quantity is critical because native vegetation constitute the main feed consumed by grazing animals in communal areas [10] [11]. The sustainability of rangelands requires a broader understanding on how grazing management systems may influence forage quality and diversity [10] [12].
Inappropriate application of rangeland management practices such as uncontrolled grazing has a profound effect on responses of herbaceous layer in terms  [13] and nutritive value [10]. Therefore, understanding the nutritional status of native grasses, their dry matter yield and the dynamics of plant species in a community is vital for sustainable livestock production [10]. Changes of weather patterns also create favourable conditions to alien plants, as a result, many grassland ecosystems in Africa are experiencing the introduction and spread of species previously unknown in the grazing communities [14].
The presence of such woody invasive species, most of which undesired by grazing animals is posing a danger to the sustainability of livestock production since their presence is negatively affecting the growth and existence of desired herbaceous species [14]. In the current circumstance, there is the need to understand the effect of the grazing management system employed and the presence of invasive woody species on relative frequency, dry matter yield and nutritive value of the herbaceous layer in grassland communities in the Eastern Cape Province. The objective of this study therefore is to evaluate the short-term impact of grazing exclusion and continuously grazed rangeland on nutritive value, relative frequency and biomass production of selected grass species in the invaded grassland communities.

Site Description
The study was conducted at Mxe communal rangelands in Cala, Sakhisizwe local municipality under the Chris Hani District of the Eastern Cape Province. The area lies at 31˚32'39.17"S, 27˚37'22.73"E, with an elevation of 4017 m ( Figure 1).
The mean annual rainfall ranges between 430 mm -790 mm, while the mean annual temperature varies from 14.7˚C to 37˚C [15]. Tsomo grassland is the vegetation type, which is characterised by gently-sloping lowland plains intersected by mountains [15]. The herbaceous layer is dominated by white grasses which are often grazed short or replaced by Euryops floribundus. Soils were derived from two parent material namely mudstone and shale [15]. Grazing capacity for the areas ranged from 4 -8 hectare per large stock unit [16].

Research Layout
Research site was chosen based on vegetation uniformity and land use type being grazing [17]. In November 2018, a plot of 2.5 hectares was measured and boundaries demarcated using a tape measure and metal pegs. The plot was further divided into two subplots, each measuring 1ha with the two subplots separated by

Sampling Procedure
In December 2019, data were collected after 12 months of rest (fallow) and

Nutritional Value Analysis of Dominant Grasses Species
Three dominant grasses species at both GE and UG sites were selected and harvested to determine the nutritive value. The selection of dominant grass species was based on the relative frequency percentage (those with high relative frequency (%) were selected, three grass species per site as shown in Table 1). Six After harvesting, samples of the same species per site were combined to form one sample per grass species. Therefore, three samples per site were store on well labelled paper bags and transported to Dohne Agricultural Development Institute for Laboratory analysis. All samples (six) were oven dried at 65˚C until constant weights were obtained and later milled to pass through 1mm sieve to determine their nutritional value. The selected species were Aristida congesta, Eragrostis chloromelas, Eragrostis plana, Hyperrhenia hirta and Themeda triandra [12]. Ash content was analysed following the method of AOAC (1990). Nitrogen (N) was determined by the micro-Kjeldahl method [19]. Crude protein (CP) was calculated as nitrogen (N) × 6.2. Acid detergent fiber (ADF) and neutral detergent fiber (NDF) were determined using the procedure of [20].

Data Analysis
The recorded data were captured in an Excel spreadsheet for descriptive statistics. However, Analysis of Variance (ANOVA) was performed for the forage yield and quality parameters (Ash, CP, ADF, NDF and biomass). The T-test of [21] was used to compare mean differences between GE and UG subplots.

Effect of Exclusion and Continuous Grazing on Herbaceous Vegetation
The results showed that grazing exclusion facilitated grass species diversity, subsequently, thirteen and sixteen grass species were identified at the UG and GE sites, respectively (

Effect of Grazing Exclusion and Uncontrolled Grazing on Dry Matter Yield
The results showed significant (P < 0.05) variation in terms of dry matter yield between GE and UG sites (Figure 2). The highest dry matter yield was recorded at the GE (1400 kg·ha −1 ) compared to the UG site (1102 kg·ha −1 ) (Figure 2). This finding is in agreement with previous work by [25]. The effect of GE on dry matter herbaceous layer dry matter production of herbaceous species indicated an increasing trend compared to the UG. This finding was expected because the site was spared the effect of grazing and any other disturbance from herbivores.
In the absence of grazing, herbaceous species were allowed to reach the maturity phase and complete their life cycle. Means within a column followed by the same letter were not significant (P > 0.05). CP = crude protein, NDF = neutral detergent fiber, ADF = Acid detergent fiber, DM = dry matter and DSP = dominant species. Open Journal of Ecology Maturity is a crucial phase in the lifecycle of any plant. Plant maturity leads to storage reserve deposition, dormancy induction, seed coat formation, biomass yield and synthesis of protective compounds. According to [26], repeated defoliation on herbaceous layer under continuous grazing conditions potentially leads to loss of biomass yield and grass vigour. The results clearly showed that GE facilitated species abundance, plant cover and accumulation of biomass compared to UG site. This finding is in agreement with results reported in different areas of Ethiopia [5] [27], in Kenya [28] and in Tanzania [29]. This finding disagrees with the results reported by [10] who stated that the age of enclosures had no effect on grass biomass production. Another possible explanation to the variation in terms of biomass yield among sites may be due to intensity of grazing. According to [22] prolonged grazing is associated with low forage production, uprooting of grasses species and nutrient reserve depletion.

Effect of Grazing Exclusion and Uncontrolled Grazing on Nutritive Value of Herbage
Grazing management is an essential practice for the conservation of healthy plant cover and the productivity of grazing lands with the aim of improving animal performance. The ash content of Aristida congesta (10.0%) was significantly lower compared to Eragrostis chloromelas (12.5%) and Eragrostis plana (12.5%) at the UG site (Table 2). Overall, the GE site had high ash contents (13.5 % -13.7%) compared to UG site (10.0% -12.5%) ( Table 2). Higher ash content in the GE site may be attributable to higher organic matter in the soil since soil was not exposed to erosion. High ash contents may be due to high concentration of soil exchangeable bases, organic matter and soil acidity [30]. Crude protein content of individual grass species showed no significant difference between the two sites ( Table 2). In terms of crude protein contents amongst individual grasses species, Hyperrhenia hirta had high crude protein (7.8%) followed by Themeda triandra (7.6%) and Eragrostis chloromelas (7.2%) at the GE site. Whereas in the UG site, Eragrostis plana had the highest crude protein content (5.8%) followed by Aristida congesta (5.5%) and Eragrostis chloromelas (5.4%) as shown in Table 2. Although not significantly different, crude protein content was relatively lower in the UG site (5.4% -5.8%) than in the GE site (7.2% -7.8%) ( Table 2). The results indicated that crude protein content at UG was less than recommended range (6% -8%) for maintenance of wild and domestic herbivores [31]. Those in the GE site fell within the recommended range. This trend was expected because young grass leaves with high crude protein were more likely to be affected by selective grazing. Furthermore, young leaves are less resistant to the repeated defoliation. This finding contradicts with that of [10]   trend may change under long-term trial because grazing exclusion promote moribund yield and as grasses gets mature crude protein content declines. This finding is in harmony with [31], who reported that grass crude protein declines as maturity from main rain season towards the cool dry season. According to [32] and [33] crude protein content declines with the increasing age of plant and increasing plant structural components such as acid detergent fiber and neutral detergent fiber. As plants age, the proportion of senescent leaves and structural components with low nitrogen content outstrip that of young leaves with higher nitrogen content [33], this cause an overall decline in the plants' crude protein content. Animal trampling, uncontrolled grazing, soil properties and climate related factors may influence the crude fiber content [34].
Grasses in the UG site had neutral detergent fiber content (75.3% -78.9%) compared to 69.0% -7.0% for the GE site (

Euryops floribundus Density and Abundance (%) in Terms of Age Class
The results revealed that UG site had high plant density (2100 plants·ha −1 ) compared to GE site (1971 plants·ha −1 ). The UG site had 31% mature trees and 69% Open Journal of Ecology  [37]. [8] and [34] reported that high grazing pressure promotes woody plant invasion because it creates opens space for woody plant colonisation allowing net recruitment into the grazing land. Approximately 57% matured and 43% saplings were recorded at the GE site.
Sapling percentage of less than 50% indicates a slow rate of Euryops recruitment [6]. However, the existing 50% of mature tress has a great potential of outcompeting grasses for water and soil nutrients [17] [37]. This finding was consistent with other authors [6] [8] [9]. The current study showed that GE improves soil cover, which protects soils from undesirable seed to get contact with soil. UG site is more proven to the recruitment of undesirable plants due to poor soil cover caused by uncontrolled grazing. The most effective method of improving degraded rangeland condition is to restore natural vegetation by excluding grazers.

Conclusion and Recommendations
In conclusion, GE was found to have a positive impact on the relative frequency (%) biomass production (kg·ha −1 ) and crude protein content compared to UG sites. Decline of species diversity, forage production and high density of Euryops floribundus is associated with continuous grazing. Continuously grazed rangeland creates a conducive condition for Euryops floribundus recruitment. This study showed that grazing exclusion has a potential to restore strong perennial grasses and improve rangeland productivity which is key for sustainable livestock production. Regardless of challenges faced by communal farmers, the results can be used as guide to track vegetation changes caused by grazing management system used. In addition, these findings provide a baseline information on potential effects of grazing management might cause on nutritional quality, species diversity and forage production. Long-term research is needed to examine grazing exclusion as potential restoration technique at different conditions (i.e. season, rainfall and slope).