Die gebruik van degradasiegradiënte vir weiveldevaluering in 'n semi-ariede gebied

Abstract

English: 1. The objectives as determined for this study are; * to classify the main land types in the central and southern Free State into homogenous plant communities; * the quantification of rangeland condition in every homogenous plant community by means of degradation gradients; * to develop easily and quick implementable techniques which can be used by land users te determines rangeland condition (these techniques must be scientificaily acceptable) and * to determine correlations between rangeland condition and grazing capacity. 2. The study was performed in the semi-arid region of the central and southern Free State and includes 35 different land types in the magisterial districts of Zastron, Rouxville, Wepener, Smithfield, Dewetsdorp, Reddersburg, Bloemfontein, Brandfort, Excelsior, Theunissen, Winburg, Thaba Nchu, Senekal, Petrusburg, Boshof, Bultfontein, Edenburg, Trompsburg, Bethulie, Jagersfontein, Fauresmith, Philippolis, Koffiefontein, Jacobsdal, Ventersburg, Virginia, Hennenman and Hoopstad, also includes bordering areas in the magisterial districts of Kimberley and Barkly West in the North Cape province. The study area forms part of a summer rainfall area with a long term average rainfall from approximately 300 mm in the west to 680 mm in the east. 3. With the use of multivariate analysis the study area was classified into 13 different homogenous plant communities which vary from a sour grass- to a mixed sour grass- to sweet grass- to false karoo- to karoo- to a savanna veld type. Degradation gradients were described by means of the ISPD system for every homogenous plant community. This degradation gradients varied from poor denuded rangeland, around water troughs, to well-managed rangeland on the first axis, while degradation on account of selective grazing also occurred on single occasions. 4. The ecological value of species was determined by means of the Gaussian distribution curve. To facilitate the ecological value of species, an index was set up that varied from zero to ten. 5. Indicator species were identified for the study area by looking at the relationship between individual species and the degradation gradients. Dominant indicator species were also identified that made the most important contribution to veld composition at one stage or another on the gradients. 6. Correlations between degradation and effective soil depth, texture and chemical soil characteristics of top soils was determined for each homogenous plant community. At wet and half-wet climate zones it was mainly the P-content that increased during degradation. At the half -dry and dry climate zones degradation leads to a loss in effective soil depth, while texture changes occurred more frequently. 7. As computer equipment can limit the use of the degradation gradient, easier alternative methods were investigated. The main advantage of this technique is that the operators need only to know the key species, that can drastically increase the utilisation value of these techniques. 8. Grazing capacity calculations were done for sheep as well as cattle at every locality. The preference utilisation ratio of species was used to determine the utilisation production for every production plot. Where the grazing capacity's were mostly subjectively determined in the past, a more objective approach was used in this study. 9. With the exception of some homogeneous plant communities, good correlations were determined between rangeland condition and grazing capacity. Exceptions did occur in the Themeda-Cymbopogon mixed sourveld, the Pan-turf Veld and the Broken Parkland where additional data should be collected. 10. Finally the most important characteristics of rangeland condition according to the changing in botanical composition of dominant species, soil changes, and grazing capacity recommendations for both sheep and cattle are tabulated for homogenous plant communities. Land users and operators can use these tables with confidence to estimate the condition and potential of rangelands. If this rangeland evaluating techniques are linked to rangeland management if would ensure sustainable utilisation of the grazing ecosystem.Afrikaans: 1. Die doelwitte wat vir die studie gestel is, is om; * die belangrikste landtipes in die Sentrale en Suid-Vrystaat in homogene plantgemeenskappe in te deel; * die kwantifisering van veldtoestand in elke homogene plantgemeenskap deur middel van degradasiegradiënte; * die ontwikkeling van eenvoudige en vinnig uitvoerbare tegnieke wat grondgebruikers kan toepas om veldtoestand te bepaal, maar tegnieke wat wetenskaplik aanvaarbaar sal wees en * die vasstelling van verwantskappe tussen veldtoestand en weidingkapasiteit. 2. Die studie is uitgevoer in die semi-ariede gebiede van die Sentrale en Suid-Vrystaat en sluit 35 verskillende landtipes in wat in die landdrosdistrikte Zastron, Rouxville, Wepener, Smithfield, Dewetsdorp, Reddersburg, Bloemfontein, Brandfort, Excelsior, Theunissen, Winburg, Thaba Nchu, Senekal, Petrusburg, Boshof, Bultfontein, Edenburg, Trompsburg, Bethulie, Jagersfontein, Fauresmith, Philippolis, Koffiefontein, Jacobsdal, Ventersburg, Virginia, Hennenman en Hoopstad geleë is, terwyl dit ook oorgangsgebiede in die landdrosdistrikte Kimberley en Barkly West van die Noord-Kaap insluit. Die studie-area is in In somerreënvalgebied geleë met In langtermyn gemiddelde jaarlikse reënval wat varieer vanaf ongeveer 300 mm in die weste tot so hoog as 680 mm in die ooste. 3. Met behulp van meerveranderlike tegnieke is die gebied in 13 homogene plantgemeenskappe ingedeel, wat gewissel het vanafh suurgras- tot 'n gemengdesuurgrastot soetgras- tot skynkaroo- tot karoo- tot 'n savannaveldtipe. Degradasiegradiënte is met behulp van die ISPD pakket vir elke homogene plantgemeenskap beskryf. Hierdie gradiënte het gewissel vanaf swak uitgetrapte veld, rondom waterpunte, tot goed bestuurde veld op die eerste as, terwyl degradasie as gevolg van selektiewe beweiding in enkele gevalle ook voorgekom het. 4. Ekologiesewaardes van spesies, is vir elke gradiënt met behulp van die Gausiese verspreidingskromme bepaal. Om die ekologiesewaarde van spesies te vergemaklik is 'n indeks wat van nul tot tien varieer het opgestel. 5. Indikatorspesies is vir elke homogene plantgemeenskap bepaal deur die verwantskap tussen individuele spesies en die degradasie gradiënte te bestudeer. Dominante indikatorspesies is ook geïdentifiseer wat op een of ander stadium op die gradiënte die belangrikste bydrae tot die samestelling van veld lewer. 6. Verwantskappe tussen degradasie en die effektiewe gronddiepte, tekstuur en chemiese eienskappe van die bogronde is ook vir elke homogeme plantgemeenskap beskryf. By die nat en halfnat klimaatsones het veral die P-inhoud tydens degradasie verhoog. In die halfdroë en droë klimaatsones lei degradasie tot h verlies in effektiewe gronddiepte, terwyl grondtekstuur veranderings ook meer algemeen voorgekom het. 7. Omdat rekenaar toerusting die gebruik van die degradasiegradiëntmetode kan beperk, is makliker alternatiewe sleutelspesie tegnieke ondersoek en teen die degradasie gradiënte getoets. Die groot voordeel van hierdie tegnieke is die feit dat die opnemer slegs enkele sleutelspesies moet ken, wat hierdie tegnieke se gebruikerswaarde drasties kan verhoog. 8. Weidingkapasiteitberekenings is vir skape sowel as beeste op elke lokaliteit gedoen. Die verhouding tussen die gemiddelde persentasie benutbaarheid van plantspesies is gebruik vir die berekenings van benutbare produksie vir elke produksieperseel. Waar weidingkapasiteite in die verlede hoofsaaklik op subjektiewe waarnemings gegrond was, is meer objektiewe waardes met hierdie studie bepaal. 9. Met die uitsondering van enkele homogene plantgemeenskappe is goeie korrelasies tussen veldtoestand en weidingkapasiteit verkry. Uitsonderings het by die Themeda- Cymbopogon-gemengde suurveld, die Pan-turfveld en by die Gebroke Parkland voorgekom waar addisionele data ingesamel sal moet word. 10. Laastens is die belangrikste eienskappe van veldtoestand ten opsigte van die verandering van die plantegroei samestelling van dominante spesies, grondkundige veranderings asook weidingkapasiteit aanbevelings vir beide skape en beeste vir homogene plantgemeenskappe getabuleer. Hierdie tabelle kan met vertroue deur grondgebruikers en veldbeamptes as keurkaarte gebruik word vir die skatting van die toestand en potensiaal van veld. Indien hierdie weiveldevalueringstegnieke aan veldbestuur gekoppel word, sal dit die volhoubare benutting van die weidingekosisteem verseker.