Patternsof invasion and dispersal of an exotic introduced weed: A case studyof OchnaSerrulata
inthe Bellingen Valley, New South Wales
Thisresearch will examine the patterns of invasion of Ochna Serrulata.The research will examine the pattern of distribution of the weedacross the Belingen Valley. The research will also examine the roleof birds as dispersal agents in the spread of the weed. The studywill also assess the potential impact of the plant on a study siteand based on the result, explain the plants potential impact if itspreads to the north coast. Lastly, the study will gatherinformation on the limiting factors of the invasion.
OchnaSerrulata was originally introduced into Australia as an ornamentalshrub. The plant has a dark green glossy leaves with bright yellowflowers and bears small red and black fruits that attract the birds.The most common birds that it attracts include bovvered birds,pigeons, currawongs and rosellas. The plant is native to southernAfrica mainly in Lesotho, Swaziland and South Africa. It wasintroduced as a garden plant and was often planted as a hedge. It iscommonly seen growing in various parts of Australia. The plant isalso becoming relatively common in coastal districts of central andnorthern New South Wales. Factors that influence inversion vary fromcommunity based factors to potential disturbance to the plant itselfby its environs. The organic traits of invaders have effect onpredisposition and spread of the plant of subject. The researchfocuses on biological features of invaders and the habitualcharacteristic of the invaded location. Disturbance that facilitateplant inversion by overcoming physical and environmental barriers aswell as other factors such as streams that may provide corridors forinversion are critical factors that deserve analysis in any research.The paper focuses on the role of dispersal mechanisms, biologicalbarriers as well as environmental barriers in explaining the spatialpatterns of the exotic plant species.
OchnaSerrulata grows as a weed in subtropical regions. However, it is alsofound in warm tropical and temperate environments. The plants maindistinguishing features are a rough pimply-textured bark,alternatively arranged leaves, bright yellow flowers with sepals thatare initially green but slowly turn bright red as they ripen. Theplant is perennial with an erect habit growing one-two meters tall.In some instances, the plant can reach three meters. The plant hasbeen declared noxious in several states and territories inAustralia. In New South Wales, the plant is categorized as a class 4locally controlled weed. The growth and spread of the plant arecontrolled according to specified measures.
Purposeof the research
Thepurpose of this study is to examine the patterns of invasion of OchnaSerrulata.
Theresearch will examine the pattern of distribution of the weed acrossthe Belingen Valley. The research will also examine the role of birdsas dispersal agents in the spread of the weed. The research will alsoassess the potential impact of the plant on a study site and based onthe result, explain the plants potential impact if it spreads to thenorth coast. Lastly, the study will gather information on thelimiting factors of the invasion
Importanceof the study
Theresearch will shed light on possible control mechanisms that can beemployed to reduce the impact of the invasive species on theenvironment. The plant widely dispersed by birds that feed on itsfruits and dump their waste on farmlands and suburban gardens. Theplant readily outcompetes the native specifies and, therefore,threatens the region’s biodiversity. In addition, the plant is hardto remove manually as it has an extended taproot. Any root remainingcan also reshoot. A proper control mechanism therefore needs to beeffected.
Scopeof the research
Theresearch is limited to the Belingen Valley in the New South Wales. Itspecifically examines the invasive species Ochna Serrulata and therole of various birds as dispersal agents in the spread of the weed.The study will include duration of one year from the date in order toexperience the year-round fruiting of the species. Lastly, the scopedoes not cover other invasive species that may be identified in theareas under study.
TheDepartment of Natural Resources declares a given plant speciesprohibited if it is invasive, if it makes significant maintenanceproblems and also if it is toxic or dangerous to humans and animals.Invasive species out-compete the native flora and fauna and becomedominant in the areas where they are found. Invasion mechanismsinclude re-growing from leaves, stems, rhizomes, bulbs or tubers.Other invasive mechanisms include wide dispersal of seeds throughwind, water and animals or heavy drop of seeds at concentratedplaces. Ochna Serrulata is an invasive plant species and causesannihilation of native plant species (White & Vivian-Smith, 202).
Severalresearch works have been carried out examining the interactionbetween dispersal agents and invasive species. In most fleshy-fruitedspecies, birds play the most significant role in spreading seeds thatin turn ruins the biodiversity of the region. The relationshipbetween weed and their dispersal agents is complex and difficult tomanage and a comprehensive study is needed to determine the extent ofthe relationships.
Whiteand Vivian-Smith (2011, p. 195-202) explain that many invasive andnative plant species in subtropical Australia depend on a sharednumber of frugivores to disperse their seeds. These are mostly birds,and occasional rodents. Most native plants in the area produce fruitduring the summer, but most invasive plants species produce fruitduring the winter. This provides an opportunity for the frugivores todisperse seeds under the synchronously fruiting species. In theirstudy, White and Vivian-Smith sampled native and invasive seed rainunder the Guioasemiglauca, anative summer-fruiting tree. The research also studied Cinnamomumcamphora, aninvasivewinter-fruiting tree in threestudy sites. The research was conducted over a passage of a year.
Theresearch found that in July, which is the peak fruiting season forCinnamomumcamphora aswell as other invasive species, the seed rain of the invasive specieswas higher beneath Cinnamomumcamphora thanG.semiglauca.The researchers attribute this to the presence of Ligustrumlucidum, aninvasive tree. L.lucidum seedrain was 3 times higher under
Cinnamomumcamphora thanunder the native trees. In the month of February, there was morenative species seed rain under G semiglaucacanopythan under that of C.camphora. Thisis despite the fact that C.camphora wasin its fruiting season. The researchers attributed this to thepossibility of G.semiglauca producinglarger fruit crop at the time of the year. The study concluded thatthe presence of invasive plants that are dispersed by birdsfacilitate contagious seed dispersal of other invasive species. Inthe same way, the researchers observed that native species couldpromote the spread of seeds of their native counterparts. The factorsemanating from the environment that favor these plant establishmentsare probably the most important during the inversion stage becausethe seeds that are introduced compete with the already establishedflora that is beyond doubt well found in the site. Diverse plantcommunities aid in maintaining vigorous ecosystems and as a result,exotic plant inversion diminishes with this increased plant diversitywithin the same setting or environ. It is, therefore, evident thatfactors that affect the rate of introduction are externalenvironmental factors that are extinct from the biology of the newlydisseminating plant seed.
Gosperand Vivian-Smith (2010, p.2153) observed that vertebrates play asignificant role in seed dispersal of fleshy-fruited alien invasiveplants. However, Gosper and Vivian-Smith decries that little is knownabout the comparison between the dispersal of indigenous fleshyfruits and their alien counterparts and how their differences resultin success of the invasive species.
Gosperand Vivian-Smith study characterized a total of 34 fruit species andexamined variables such as their pulp nutrient, morphology as well astheir phenology to determine how their differences contributed totheir invasive success. The chosen fruits were all vertebratedispersed alien species gathered from southeastern Queensland,Australia. Most of the sampled fruits were small with 81% having amean width smaller than 15 millimeters in diameter. The researchersfound that alien fruits have significantly smaller seeds compared totheir indigenous
counterparts.In addition, alien seeds had more sugar in their pulp nutrients aswell as higher levels of nitrogen and lipids. Besides, the alienspecies had longer fruiting seasons compared to the indigenousspecies. They concluded that the fruit characteristics were importantdeterminants of invasiveness and could be used to promote inassessing the risk of invasiveness. The inflow of exotic plantspecies to new regions is a continuous process and from research, itis only few of the alien species that become established in these newenvironments and further, a subtle proportion of the establishedspecies become invasive. Most of these invasive species havesubstantial lag time between introduction into a new site andsubsequent population growth in that particular area. Disturbance,which is the damage of the plant biomass, is a commonly believed tobe a major factor favoring introduction and the invasion process.
Disturbanceis a situation whereby the entire ecosystem is disrupted so that somenew forces intervene in the normal and general processes that theplants in a given environment are familiar with. It may result fromfire and storms among other large scale events and even from minorevents like vegetation removal by animals. Besides, environmentalfactors that limit vegetation growth also contribute to invisibilityof the plant species. The disturbance as a result may lead to atemporary location of the plant for possible aggressive species toestablish a founding group.
Vivian-Smithand Gosper (93-4) examined the effect of invasive species Asparagusaethiopicus andAsparaguAfricanus insubtropical Australia. They also examined a third species, AsparagusVirgatus thatdemonstrates localized spread within southeast Queensland. Theresearchers compared their fruit and seed characteristics, seedsurvival, germination, seed rise and the time they took to mature.The researchers also investigated the A.Africanus,dispersal ecology by studying the diet of the figbird, a localfrugivore (called Sphecotheresviridis).They examined the effect of passage of the seedling in the bird’sgut and its impact on the emergence of the seedling. They found thatthe A.Aethiopicus hada superior germination and emergence rate with an overall germinationand emergence rate of 98.8% and 64.5% respectively. However, A.Africanus exhibitedthe lowest germination and seedling emergence rates given optimalconditions (71.7% and 49.5% respectively). That said A.Africanus fruitshad the highest relative yield as measured by the ratio of fruitfresh weight to dry pulp. The high relative yield was favored by thelocal frugivore and thus consumed higher amounts of A.Africanus fruitsby 30%. A.Africanus seedlinggermination was not affected by passage in the bird’s gut ascompared to unprocessed fruits.
Thestudy further found that AsparagusVirgatus seedshad poor rates (1.4%) of germination under light and cool conditions.This is despite their high optimum average of
95.0%and a low mean performance in all other emergence treatments (36.3%).Asparagusvirgatus’sfruits had low relative level of nutrients for the frugivores. Theresearch concluded that the A.virgatus speciesis not likely to exhibit invasive potential compared to itscongeners. They further concluded that short seed survival times meanmanagers do not need to be concerned about the seed banks in thesoil. Rather, managers will have a considerable challenge fromfrugivore-mediated dispersal.
Gosperand Vivian-Smith (2009, p. 196) explains that despite the invasiveplants’ threat to biodiversity, they play an important role inrestoring heavily modified landscapes such as quarries and disusedspaces. They explain that invasive species play an important role insustaining native frugivore populations. The researchers point to aconservation conflict as exterminating the invasive species leads tothe unintended consequence of exterminating native populations ofother species. The researchers originate a plan for ranking nativeplants that produce fleshy- fruits based on their ability to producethe fruit resources for native frugivores that are currently beingobtained from invasive plants. The researchers explain that thenative species should be preferentially planted based on theirecological appropriateness in restored and reclaimed settings tosupport native birds. This, they explain, should be done in the eventthat extensive control mechanisms result in the extermination of theinvasive species.
Theresearchers developed a model to rank the native species using amultivariate approach based on the frugivore assemblage. Theyoriginate a scoring model that takes into account several variablesincluding traits combinations, fruit morphology, conspicuousness,phenology, and accessibility. They conclude that the authoritiesshould adopt a replacement approach that uses ranking using alltraits available. Alternatively, the researchers explain thatauthorities can replace the invasive species using the prevalentfrugivore community as a guide to the most favorable native plants.
Asexplained before, the resolution of this study is to observe thepatterns of invasion of
OchnaSerrulata across Belingen Valley. The research resolves to adopt botha qualitative and quantitative research design to answer the researchquestions. Also, included in extermination is the role of birds asdispersal agents in the spread of the weed within the area. Theresearch will also evaluate the potential impact of the plant on astudy site and based on the result, explain the plant’s potentialimpact if it spreads to the north coast. Lastly, the research willgather information on the limiting factors of the invasion.
Dependingon the allocated budget, appropriate survey method will beincorporated to collect insolence data from those who shallparticipate. The questionnaire will be based on the Likert methodwith all items in the survey being tested and analyzed.
Theresearch will answer the following research questions:
a)Whatare the patterns of distribution of Ochna Serrulata in Belingenvalley?
b)Whatis the role of birds as dispersal agents in the spread of the weed?
c)Whatis the potential impact of the plant on Belingen Valley and based onthe result, what is the potential impact if it spreads to the northcoast?
d)Whatare the main limiting factors of the invasion?
Datawill be collected from Belingen Valey relating to the population ofOchna Serrulata and its effect on the local population. The study isaimed at collecting random sample from the entire Ochna Serrulatapopulation. The strata samples will be place of residence be it townor non-town and this will be able to provide accurate information forfinal analysis to be made. A pilot study will be done to test themethod and to figure out the sample sizes to be used in the researchproposal. Computer assisted techniques may be used to assist infilling findings and to reduce other unnecessary costs. This willalso improve the response rate which facilitates good data analysis.
Gosper,CR and Vivian-Smith, G 2010, Fruit traits of vertebrate-dispersedalien plants: smaller seeds and more pulp sugar than indigenousspecies, BiologicalInvasions 12(7):2153-
Gosper,CR and Vivian-Smith, G 2009, Approaches to selecting native plantreplacements for fleshy-fruited invasive species, RestorationEcology 17(2):196-204.
Gosper,CR and Vivian-Smith, G 2009, The role of fruit traits ofbird-dispersed plants in invasiveness and weed risk assessment,Diversityand Distributions 15(6):1037-1046.
Vivian-Smith,GE and Gosper, CR 2010, Comparative seed and dispersal ecology ofthree exotic subtropical Asparagusspecies,InvasivePlant Science and Management 3(1):93-103.
Vivian-Smith,G and Panetta, FD 2009, Lantana (Lantanacamara)seed bank dynamics:
seedlingemergence and seed survival, InvasivePlant Science and Management 2(2):
White,E and Vivian-Smith, G 2011, Contagious dispersal of seeds ofsynchronously fruiting species beneath invasive and nativefleshy-fruited trees, AustralEcology 36(2):195-202.