EFFECT OF UNGULATES (BISON) ON PLANT DENSITY
EFFECTOF UNGULATES (BISON) ON PLANT DENSITY
Thisstudy was conducted in accordance with the need to understand howbiodiversity could be affected by grazing, particularly bison grazingin the experiments, which is one of the most common ways farmers,ecologists, and environmnetalist manage different ecosystems, due toits efficiency and cost effectiveness. Knowledge derived from thisstudy will be indispensible in understanding how grazing could bemanaged to control biodiversity in a given ecosystem. Accordingly,this laboratory exercise investigated the effect of the presence andabsene of ungulates (bison) grazing on the biodiversity of plant lifeon the watersheds of Konza Paririe LTER in Kansas. It alsoinvestigated the effects of varying levels of grazing to the level ofdiversity of four tall grass pspecies, expressed as the amount ofplant biomass produced. In other worsds it answered the questions:how does grazing and the degree of grazing do to plant biodiversity.This study utilized the data gathered on the biomass of planst aswell as the information on the number of plant species of 20 plotscollected during the year 2004 on the watersheds of Konza ParirieLTER in Kansas. Simple statistcal anslysis was done in this data inorder to compared the different parameters which includes: presence or absence of bison, density of bison, plant biomass, and plantdiversity. Results from the experiment revealed that grazing can beused to increase and maintain biodiveristy. It also revealed thatgrazing should be done in moderation as too much garzing could alsopose adverse effects to biodiversty. Grazing, therefore, is apowerful method in managing plant biodiversty. Framers, ecologists,and evironmentalist should therefore utilize this simple method inresering biodiversity in different ecosystems of our environment.
Biodiversity is important in maintaining the stability of anecosystem. It is due to this reason that environmentalist are workinghard to preserve biodiversity or induce it on areas were an imbalancebetween different species takes place. Maintainig biodiversityinvolves the control of the population of different species whetherthey be plants, microorganisms, or animals. When one species overpopulate a certain area, another species will definitely decrease itssize – especially when there is a predator-prey relation shipbetween them. Maintaining biodiversity is also important inmaximizing the carrying capacity of a certain ecosystem. Fortunately,there are varying ways to preserve biodiversity. One these ways isgrazing. Grazing is a term pertaining to the process by whichanimals, usually herbivores, consume diverse plant species within anarea regularly at consistent or regular time interval. Grazing isusually practiced by farmers in order to preserve the richness andintegrity of the soil. Nevertheless, too much grazing could alsoresult into a loss of biodiversity especially if the herbivoresconsume a very narrow variety of plant species present in the area.Hence, it is important to understant how much grazing activity isessential to optimize the population of each plant species in aparticular ecosystem. There are varying ways to measurebiodiversity, and one of these ways is the measurement of the speciesrichness, which is basically the number plant species present withina particular area or ecosystem. Another method is the determinationof each plant species’ biomass. In this exercise the effect ofUngulates (Bison) grazing on plant biodiversity was investigated. Theecosystem or the area studied was the Konza Paririe LTER wathershedsin Kansas.
The method used in this exercise is the measurement if speciesrichness. The species reachness of grass plant species in KonzaParirie LTER watersheds in Kansas was determined. This was done bycreating a species accumulation curve. This curve was created byplotting the number of species of plants found (dependent variable)on different number of plots or number of sampling (independentvariable) within the watersheds. There where two experimentaltreatments all in all, or two different watersheds where speciesrichness measurement was carried out: Bison-present, andBison-absent. Bison-present is the experimental treatment where thewatershed was grazed by a bison herd for 14 years, while Bison-absentis the eperimental treatment where the atershed was protected fromgrazing for 25 years. The peaks of the curves, or the area of thecurves where there is no more change in the value of the dependentvariable were determined. These peaks are the representatives ofspecies reachness.
The effect of the absence and presence of bison grazing on four tallgrass plant species biomass production – which is an indication ofthe level of growth for each of the tall grass plant species – wasalso studied in this exercise. The four plant species were:Andropogon gerardii, Sorghastrum nutans, Amorpha canescens, andAmbrosia psilotachy. Accordingly, the biomass of these plantspecies were determined in two aforementioned experimentaltreatments: Bison-present and Biso-absent. The biomass for eachspecies was expressed in terms of frequency, which Iis defined as,“the propotion of total sample plots in which that species wasfound” (Laboratory manual, date, page).The relative abundance with is the relative frequency, which is alsothe relative abundance of each species with each other was alsocomputed. The relative frequency was computed by taking the frequencyof each species and then dividing that by the sum of all thefrequencies in the community.
This exercise has also investigated the effects of different levelsof Bison Densities on biodiversity of the fore aforementioned tallgrass plant species. Accordingly, the experimental treatments weremade: Low Bison Density, Medium Bison Density, and High BisonDensity. The plant biomasses were measured in each experimentaltreatment and were compared.
The Simpson Index was also computed to provide a quantitative measureof biodiversity between Bison-present and Bison-absent. The resultswere shown on tables and bar graphs for easier interpretation andorganized presentation.
3.1 Determinationof Species Richness
Based from the species accumulation curve, the number of plots wherethere is an insignificant increase in the number of plant speciesbegins at 20. At this number of plots there are 92 different plantspecies for Bison-present experimental treatment and 54 for theBison-absent experimental treat.
Figure 1:Species accumulation curve for plant species at the watersheds ofKonza Paririe LTER
3.2 Plant Biomassand the Presence or absence of bison grazing
Results of the experiment investigating the effect of grazing to theamount of plant biomass shows that the experimental treatmentBison-absent shows a less balanced distribution of biomass among thefour tall grass species: Andropogon gerardi, Sorghastrum nutans,Amphora canescens, and Ambrosia psilotachya. It should be notedin figure 2 that discrepancy between the biomasses of Andropogongerardi and Sorghastrum nutans to Amphora canescens andAmbrosia psilotachya is relatively large in the Bison-absenttreatment compared to their discrepancies in the Bison-presentexperimental treatment. The decrease in the discrepancy is due to thefact that the biomass of Andropogon gerardi and Sorghastrumnutans decreased whiles the biomass of Amphora canescensand Ambrosia psilotachya increased by grazing. Grazingtherefore helps in the balance of the four plant species populationin the watersheds of Konza Paririe LTER. Figure 2 illustrates thisdifferences.
Figure 2: Effect ofpresence and absence of bison grazing on the amount of biomass offour tall grass plant species at the watersheds of Konza Paririe LTER
3.3 Plant Biomassand Different Bison Density
Results from thedetermination of the effect in plant biomass production of varyingbison density showed that there is a similar distribution of plantbiomass for each of the four tall grass plant species for Low DensityBison and High Density Bison. Nevertheless, the overall biomass forthe High Density Bison is relative lower to that of the overallbiomass of the Low Density Bison. What this means is that when thereis relatively high density of bison in the watershed, they tend toconsume more of the four types of tall grass plant species hencedecreasing all their total biomass. When there is medium density ofbison, however, the distribution of plant biomass among the four tallgrass species becomes more balanced. This means that the bison tendto consume more of the Andropogan gerardi and Sorghsatrumnutans and less of the Amorpha canescens and Ambrosiapsilotachya allowing the two latter species to grow more whiledecreasing the growth of the two former species, hence slightbalancing the biomass distribution among the four species. Theseresults are summarized in figure 3.
Figure3:Effects of varying the level or density of grazing bison on thebiomass of tall grass plants species at the watershedsof Konza Paririe LTER
3.4Relative Abudance of Plant Species and Different Bison Densities
Resultsin the analysis of the relationship between different Bison densitiesand relativeplant species abundance is shown in figure 4.Accordingly, Medium Bison Desnity experimental treatment showed ablanced abundance among the four tall grass plant species. There isan imbalance for voth High Bison Density and Low Bison Densitytreetments, however.
Figure4: Relative abundance of plant biomass of the four tall grassspecies expossed to different bison densities at the watersheds ofKonza Paririe LTER
3.5 The Simpson’sIndex
To provide a quantitativedescription of the difference in plant species diversity betweenBison-present and Bison-absent, the Simpson Index (D) was computed.Results showed that Bio-present scored 0.977 while Bison-absentscored 0.969. This difference in value indicate difference in speciesdiversity between the two experimental treatements accordingly,Bison-present had higher species diversity that Bison-absent. Thisresult reinforces all the findings aforementioned on previoussubsections that grazing helps maintain biodiversity among plantspecies at the watersheds of Konza Paririe LTER.
Table1:Comparison of Species Diversity in the presence and Absence of Bisonusing Simpson Index
Simpson Index (D)
The difference in the number of plant species for the same number ofplants between Bison-present and Bison-absent clearly indicates thatgrazing at the watersheds of Konza Paririe LTER increases biodiversty(see figure 1). Moreover, the impliation of the results shown infigure 2 and 3 means that sufficient grazing could lead to theefficient control and maintenance of plant species diversity within aparticular area. These results suggest that in order to maintainbiodiversity, it is necessary to determine the number of bison orgrazers in general that could graze on a certain area. The rightnumber of grazer is that which maximizes the balance of biomass amongplant species which they graze upon. These findings are confirmedquantitatively by the Simpson’s Index values shown in table 1.
Numerous studies have been done in determining the effects of grazingto plant biodiversity on certain ecosystems. One of these studies wasperformed by Woldu & Saleem (2000). Their study involved themonitoring of induced biodiversity of plant species at the highlandecozone of East Africa. In their study they have noted that there wasa significant difference in the distribution and biodiversity ofgrazed and ungrazed areas in the ecozone. Accordingly, grazedecozones showed more dispersed plan varieties and have higherdiversity levels compared to ungrazed areas. The authors explainedthat there are three reasons for the higher diversity in theecozones. Accordingly: the manure of the grazing animals allowsefficient fast nutrient cycling in the soil the grazing animalsdisperse the seeds of the plants causing a more varied distributionand grazing allows the sunlight to reach smaller plants below biggerplants – in other words, grazing facilitates the equal distributionof resources for the many different species of plants to survive andgrow. In another study conducted by Verdu, Crespo & Galante(2000), they have shown that grazing can increase diversity amongdifferent plant and animal species at the Font Roja Natural Part inAlicante Province, South East Iberian Peninsula. Their explanationfor such results is that grazing balances the access to nutrient,food, and sunlight access among plant and animal species. For examplewithout grazing plants which grow faster would eventually blocksunlight for other smaller or slow growing plants. Grazing, however,prohibit such sun blocking as grazer would usually eat more of thatwhich is more abundant. The manure which grazing animals produce alsocontribute to the efficient processing of nutrients and can serve asfood for other animal species, particularly the insects such as thedang beetle. Similar results and findings have been shown on thestudies of Jones, Fraser& Curtis (2010) Taddese, Saleem, Abyie &Wagnew (2002) and Towne, Hartnett & Cochran (2005).
Another interesting finding which supports the results of theexperiment in this research with regards to bison densities, is foundin the study conducted by Laycock (1994). In his research he hasshown that heavy grazing on small areas results to decrease inbiodiversity while moderate grazing does otherwise. He furtherexplained that the reason for such results can be explained using theconcept of carrying capacity. Accordingly, carrying capacity pertainsto the capacity of the ecosystem to meet the nutrition of thedifferent species present in it. When the demand for nutrition is toomuch for one species, the carrying capacity of the ecosystem for thatparticular species is stretched to its limit hence it could provideno more for other species. In the case of grazing, when thepopulation of grazing animals suddenly increased and they graze toomuch on grasses, the grasses’ growth will no longer be able tosustain the needs of the grazers up to the point that the grassesfail to reproduce and die. Similar results are found on the studiesconducted by Proulx & Mazumder (1998) Cingolani, Noy-Meir &Díaz (2005) and Trager, Wilson & Hartnett (2004).
From the results discussed previously and from past studies whichwere reviewed, it can be concluded that indeed, grazing has positiveeffects in the ecosystem, particularly in the maintenance ofbiodiversity. Nevertheless, it also equally important to understandthat too much grazing could cause a decrease I biodiversity. It istherefore recommended that the grazing be maintained up to the levelwhere it could facilitate the efficient balanced distribution ofnutrients and allows equal access of resources, such as sunlight,among different plant species in a particular area of concern. Thegrazing of animals should be maintained at moderate levels in orderto maintain balance in the plant species level of abundance.Moreover, the carrying capacity of the ecosystem should always beconsidered in determining the density of grazers needed to maintainrich biodiversity in it. Lastly, grazing could be one of the simplestyet best solutions to the growing problems with soil fertility inmany different countries. Grazing therefore is one of the simplestand most efficient ways by which nature balances its diversity. TheEnvironmental Protection Online (2014), explained, “The solution tosaving the biodiversity in grasslands is one that nature devised: letgrazing animals crop fast growing grasses that can out-compete nativeplants in an over-fertilized world. Grazing works in a way that isnatural and simple. The herbivores, or grazing and browsing animals,feed on tall grasses that block sunlight from reaching the ground,making the light available to other plants.” Farmers, ecologists,and environmentalist should therefore take advantage of thisefficient method in maintaining and preserving biodiversity in themany different ecosystems of the environment.
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