Impacts of Grazing on the Selected Features of Herbaceous Species and Harvested Dry Matter Yield of Natural Pasture

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Introduction
In Ethiopia, the primary source of animal feed is natural pastures, which are mainly used for grazing by livestock and other animals and are composed of native or naturally occurring grasses and other herbaceous species [1,2].However, the production and size of the natural pastures in previous research were infuenced by factors such as topography, temperature, precipitation, sunlight, soil fertility [3], expansion of cropland, expansion of aggressive plants, and overgrazing [4].Grazing, one of the most signifcant land uses in natural pastures, has an impact on the species diversity, dry matter yield, and structure of the vegetation [4][5][6].In addition to altering species diversity and dry matter yield, grazing has a signifcant impact on how vegetation communities form, the basal cover, and richness [7].Overgrazing leads to signifcant land degradation, decreased biodiversity, a decline in the nutritional value of forage plants, and the gradual eradication of native grasses in favor of less palatable and nonpalatable plant species [8].
Contrary to overgrazing, which has led to a decline in forage quality and quantity as well as the general degradation of natural pasture, appropriate grazing management shows an increasing improvement in forage value, quality, and quantity [9].According to the previous study [10], livestock grazing is seen as a reasonable solution for maintaining and improving grassland biodiversity.
Te impact of grazing on the dry matter yield and biodiversity in Ethiopia's lowland areas has been examined in various studies [11][12][13].However, there was no information available regarding the impact of grazing in Ethiopia's highland regions.Terefore, the goal of this study was to evaluate how grazing impacted specifc herbaceous species characteristics (basal cover, species richness, evenness, diversity, and dry matter yield) of natural pasture in northwestern Ethiopia.

Description of the Study Area.
Te study was carried out in the east Gojjam zone of Amhara's national regional state, Ethiopia.Te zone is located in Ethiopia's northwestern highlands between the latitudes of 10 °1′ 46″ and 10 °35′ 12″ N and the longitudes of 37 °23′ 45″ and 37 °55′ 52″ (Figure 1).It is located 300 and 251 kilometers from Addis Ababa and Bahir Dar, respectively.Te zone's elevation ranged from 1500 to 3537 meters above sea level.Te average annual rainfall is from 900 to 2000 millimeters, while the average minimum and maximum temperatures are 7-15 and 22-25 degrees Celsius, respectively.According to the East Gojjam Animal and Fishery Development Ofce, sheep, goats, cattle, donkeys, horses, mules, chickens, and bees were practiced farming systems in the zone.

Sampling Procedures.
Te study was conducted at three grazing sites: grazing exclusion areas, controlled grazing areas, and continuous grazing areas.Grazing exclusion areas were natural pastures where livestock were restricted from grazing for a period of four years.Controlled grazing areas were natural pastures that were only used for grazing for three months, from September to November, and not used for the remaining months of the year.Continuous grazing areas are pastures that are grazed all year long, having unrestricted access to the grazing unit (Table 1).All of the grazing areas have similar soil, temperatures, and amounts of rainfall.Samples were taken during the fowering stage of the forages in all grazing areas.Prior to the collection of pasture herbage samples, grazing had been excluded from the start of the pasture growth stage to maturity (fowering stage) in both continuous and controlled grazing areas.Terefore, in every grazing area, no portion of the herbage or forage was grazed or consumed before harvesting.
In each grazing site, two randomly selected (100 m × 50 m) sampling blocks were placed.Ten, each of the separated areas was divided into fve plots of 10 m × 10 m, and in each subdivided plot, three 0.5 m × 0.5 m quadrats were placed across the plots [14].Tus, a total of 30 quadrats were used to evaluate the efect of grazing on the basal cover, diversity, and dry matter of herbaceous pasture layers.

Identifcation of Herbaceous Plant Species.
Identifcations of plant species are crucial for managing grazing lands because they are used to assess the condition of the grazing land and because species composition afects dietary quality [15].To facilitate identifcation, samples were collected and identifed from August to September, when plants were at their peak fowering stages.Te herbaceous species in each quadrat were identifed on-site, and those that proved difcult to identify were transported to the Addis Ababa National Herbarium for identifcation.

Estimation of the Dry Matter Yield of Natural Pasture.
To estimate the dry matter yields of natural pasture, ten quadrats (0.5 m × 0.5 m) were placed randomly in each grazing site.Consequently, thirty quadrats in total were taken to measure the dry matter yield of natural pasture.All herbage inside the quadrat was harvested at the ground level, instantly weighed using a sensitive balance, and the weighted subsample was placed in plastic bags.To determine the dry matter yield of the natural pasture per hectare, the collected herbage was subsequently placed at 65 °C for 72 hours.Te following formula was used: where TDW is the total dry weight, TFW is the total fresh weight, SFW is the subsample fresh weight, and SDW is the subsample dry weight.
2.5.Determine Species Diversity and Evenness.Te two components of species diversity, also known as heterogeneity [16], are species richness and evenness.Species richness refers to the total number of species in a community, whereas species evenness or dominance equitability describes the distribution of species abundance among species.Diversity has become the most widely known criterion for evaluating a site's potential for conservation and ecological value [17].Te Shannon-Wiener diversity index was used to analyze the species diversity of pasture vegetation.
where H is the Shannon-Wiener diversity index, p i is the proportion of the entire community made up of species i, ln is the natural logarithm, and i is the total number of individuals (or the relative abundance of the ith species).Te Shannon-Wiener evenness index, which is the standard measure of species evenness, was used to calculate species evenness.
where E is the evenness, H is the Shannon diversity index, and S is the total number of unique species.

Species Similarity or Dissimilarity.
Te degree to which the species composition of the study area is similar is indicated by the similarity value; as a result, the manipulation of the common species in the study areas depends greatly on the similarity or dissimilarity study of a given grassland community.Te similarity-based richness of species was measured using the Czekanowski coefcient in the manner shown as follows.Te Czekanowski coefcient similarity index is where Sc is the similarity coefcient, m is the number of species,  m i�0 min(Xi, Yj) is the sum of the lesser scores of species i where it occurs in both quadrats, and Xi and Yj are abundance of species i.

Basal Cover.
Te area occupied at the points where living plant parts touch the soil is recognized as basal cover.It was estimated through the analysis of basal cover in a sample of 0.5 m × 0.5 m (0.25 m 2 ).For the surface of the basal cover of tufted grasses, the distribution was assessed as follows: the 0.5 m × 0.5 m sample area was divided into halves.One half of it was then divided into eighths.In the designated 0.5 m × 0.5 m area, all of the aboveground plant materials were cut, transferred, and kept; it has been drawn in the eighth part to facilitate visual evaluation, and the area of the rest of the plant material at the soil surface level was also estimated visually.Te basal cover as a percentage was estimated by three persons, and the average value was used for analysis.Only the basal cover of living plants was taken into account.

Data Analysis.
For the herbage dry matter yield, the data were analyzed using the general linear model procedure of SPSS (version 25).Signifcant diferences comparisons between means were tested using the least signifcant diference (LSD).Te following model was used for analysis: where y ij is the dry matter yield, μ is the overall mean, G i is the grazing efect, and E ij is the random error.

Herbaceous Plant Composition.
A total of 59 plant species, including 32 Poaceae and 27 non-Poaceae species, were identifed in the natural pasture land of the study areas.Eleven of the 27 non-Poaceae species belonged to the Fabaceae, fve to the Asteraceae family, four to the Cyperaceae family, two to the Commelinaceae family, and one to each of the other families Acanthaceae, Plantaginaceae, Resedaceae, Santalaceae, and Urticaceae (Table 2).According to the results, the percentage of species from  Poaceae (54.2%) and Fabaceae (18.6%) was identifed to be the largest in all grazing areas (Table 3), which is in line with the fndings of [18], who reported that the species from Poaceae and Fabaceae were the dominant species in the east African mountain forest.Te grazing exclusion areas had the highest proportion of species from the Poaceae family compared to controlled and continuous grazing areas.In contrast to controlled grazing areas, continuous grazing areas had a lower proportion of species from the Poaceae family.Tis is due to the fact that grazing has a signifcant efect on species composition; as grazing density increased, species composition signifcantly decreased [19].On the other hand, compared to grazing exclusion and continuous grazing areas, controlled grazing areas had the highest percentage of species from the Fabaceae family (Table 3).Tis might be due to the association ability of grass and legumes, in which grasses are taller than legumes, which highly compete for solar energy, which may be the cause of the higher percentage of species from the Fabaceae family in controlled grazing areas than grazing exclusion areas [20].
Te percentage of species from the Apiaceae, Asteraceae, Cyperaceae, Commelinaceae, Santalaceae, and Urticaceae families was higher in continuous grazing areas than controlled grazing (Table 3).Tis may be due to the probability that continuous grazing areas with higher grazing intensities have caused the spread of less palatable species.More palatable species could disappear as a result of frequent cattle grazing on highly palatable grass and legume species, whereas less palatable species may spread out as a result of intense competition for sunlight and nutrients [19,21].

Efects of Grazing on Selected Features of Herbaceous
Species and Dry Matter Yield.Te overall dry matter yield of natural pasture in the current study (2.31 t•ha −1 ) per single growing season was less than 6 t•ha −1 for well-managed natural pasture [22], 2.38 t•ha −1 [6], 4.5 t•ha −1 [23], and 5.4 t•ha −1 [24] in lowland Ethiopia.Tis variation could be caused by the amount of rainfall, the intensity of grazing, climatic conditions, and the condition of the natural pastures.It is possible that the difculty of plants surviving at higher altitudes due to low temperatures is the cause of the lower biomass production in the highlands [25].Tat is, low temperatures slow the decomposition of soil organic matter and the uptake of nutrients by roots [26].
Grazing had an impact on the selected features of herbaceous species (the basal cover, species richness, evenness, and diversity) and dry matter yield [27].In the current study, the aboveground dry matter yield in grazing exclusion areas and controlled grazing was signifcantly higher (P < 0.05) than in continuous grazing areas (Table 4), which is supported by the fndings of [5,9,28,29].Due to protection from grazing during the growth season, both grazing exclusion areas and controlled grazing areas produced higher aboveground dry matter yields than continuous grazing areas.Tis led to the recovery of the species, but year-round grazing in the continuous grazing area reduced biomass yields [30].When compared to controlled-grazing areas, grazing exclusion areas had a higher aboveground dry matter yield.As a result of no cattle grazing, which allowed for the recovery of species and the accumulation of biomass, grazing exclusion areas produced higher aboveground biomass yields [9,31].Te aboveground dry matter yield of plant communities is impacted by feeding, trampling, and other grazing livestock behaviors, which decrease plant leaf area, lower photosynthetic capacity, and alter forage structures [32].
Te continuous grazing areas had signifcantly (P < 0.05) less herbaceous plant basal cover than grazing exclusion areas and controlled grazing areas, which was consistent with the fndings of [28,[33][34][35][36].In contrast to grazing exerted on continuous grazing areas, which are vulnerable to grazing and trampling, higher basal cover in the grazing exclusion areas indicated better management and less opportunity for the vegetation to be disturbed.According to [37], grazing pressure has an impact on soil loss and compactness, which has a signifcant impact on the state of the grazing land.Tis suggests that a decline in the quality of grazing land in continuous grazing areas has a direct negative impact on livestock production [38].
Te fndings of this study were consistent with [29,39], and in that, there was a higher diversity of herbaceous plants in both grazing exclusion areas and controlled grazing areas than in continuous grazing areas.Te high species richness and diversity in the grazing exclusion areas may be related to improved soil organic matter, increased litter accumulation, and improved soil nutrients within the grazing exclusion areas [40].Another study found that the type and distribution of plants were higher in areas where there was no grazing disturbance [41].However, the lower herbaceous plant diversity and richness in continuous grazing areas were due to indirect pressure on seedling germination and establishment patterns [10,14,27,30,34,35].
On the other hand, herbaceous plant species richness and diversity were greater in grazing exclusion areas than in controlled grazing areas.Tis might be due to the fact that plant species abundance was afected by the length of grazing.Te length of time livestock is allowed to graze in a particular grazing area has a signifcant impact on vegetation variation, which afects the sustainability of the plant community within the site.If grazing rates were high, the overall vegetation pattern would decline [42,43].A longer resting period for forage plants as a result of enclosing the natural pasture, which improved seedling germination and forage plant establishment [44,45], increased species richness and diversity.Furthermore, as reported by [46], frequent grazing sites have less vegetation than less frequent grazing sites, and enclosing natural pastures increases their potential and boosts livestock productivity [47].

Herbaceous Plant Species Similarity.
Figure 2 shows the estimated Czekanowski coefcient similarity index of the herbaceous species in terms of species composition based on species richness.Te grazing exclusion areas to controlled grazing areas showed the highest similarity of herbaceous species.Te greatest diferences in herbaceous 4 International Journal of Forestry Research  species were found between grazing exclusion and continuous grazing types.Tis diference in similarity was brought about by grazing intensity.Te level of disturbance in the species composition between the sites is correlated with the degree of species similarity and difference across grazing systems [48].Tis is as a result of the reduction in livestock grazing, which allowed for the recovery of species and the buildup of biomass [9,27,34].Te degree to which the species composition of the vegetation samples from the various communities is similar is measured by the concept of species similarity.Te degree to which the species composition of the study areas is similar is indicated by the similarity value; as a result, the manipulation of the common species in the study areas depends greatly on the similarity or dissimilarity study of a given grassland community [34,49].

Conclusions
Te duration of grazing had an impact on the dry matter yield, basal cover, species richness, evenness, and diversity of herbaceous species.Te analysis showed that the dry matter yield in grazing exclusion areas for four years was in good condition, while the dry matter yield in areas that allowed for continuous gazing throughout was the lowest.Dry matter yields in controlled grazing areas were slightly lower compared to those in grazing exclusion areas.As a result, the dry matter yield and the diversity of herbaceous plants were impacted by grazing and resting periods.Terefore, to increase the dry matter yield of the natural pasture and for sustainable livestock production, the livestock producers in the study areas should use a controlled-grazing system.In controlled-grazing systems, there are more palatable plant species than in continuous-grazing areas.Tis afects the pasture's nutritional value and could eventually increase livestock production.

Figure 1 :
Figure 1: Location map of the six study areas.

Table 1 :
Te sampled grazing types and the size of grazing areas in the study areas.

Table 2 :
Te distribution of plant families and their species in three grazing areas.

Table 3 :
Te percentage distribution of plant families and their species in the three grazing sites.

Table 4 :
Impacts of grazing on the selected features of herbaceous species and dry matter yield.Means within the same row with diferent superscript letters difer signifcantly (P < 0.05) among grazing types.
International Journal of Forestry Research