Prospects for sustained harvesting of mopane (Colophospermum mopane) on the Venetia Limpopo Nature Reserve and its implications for browsing ungulates

Cunningham, Peter Low (1996-03)

Thesis (MSc) -- Stellenbosch University, 1996.

Thesis

ENGLISH ABSTRACT:Principle objectives of this study were to investigate the ecological feasibility of sustained utilization of mopane, using Venetia Limpopo Nature Reserve as a pilot study area. The study was limited to three different mopane dominated vegetation types on the reserve with most research being conducted in C.mopane woodland. Results can be summarized as follows: 1. Colophospermum mopane is ubiquitous on VLNR. 2. C.mopane woodland has the deusest mopane growth of the three vegetation types and highest densities are found on soils (OaB, VaB, Du, SwB & VaA) in association with C.mopane woodland. There seems to be a correlation between mopane density and soil type. 3. Largest mopane trees according to height and circumference were found in C.mopane/C.apiculatum open woodland. There is no significant difference between height and circumference on different soil types. 4. Most senility occurs in C.mopane shrubland and there is a significant difference in senility between mopane associated with different soils on which this vegetation type occurs. 5. Oldest average ages per tree were fo•.md in C.mopane woodland while growth rates were fastest in C.moparse!C.apiculatum open woodland. 6. There is a significant positive correlation between total and charcoal weights for mopane. Total and charcoul weights per tree were highest for C.mopane/C.apiculatum open woodland, while weights per hectare were highest for C.mopane woodland. Soils could not positively be associated with this trend. 7. Mopar.e lends itself to harvesting, especially C.mopane ••10odland in the Endora, Lizzulea and Hilda areas. Winter months seem to be most desirable for harvesting activities. Hand felling in elongated patches (increases ecotone boundary) is recommended where labour is cheap. A harvesting strategy of between 25% and 50% would make the operation economically viable and ecologically acceptable. An optimum harvesting rate of 27% is suggested by a harvesting model developed specifically for this mopane data. 8. Total herbivore densities, distribution and species proportions can be expected to change following bush clearing. Habitat for grazers should increase due to an increased grass production. Habitat for browsers should not be influenced much. Effect of noise and human disturbance during harvesting, especially for elephants is negligible, as hunting activities already take place on VLNR. 9. Grass production would increase but quality should decrease after harvesting, due to an increase in low quality opportunistic species, especially if soil disturbance takes place. Grass quality is best in association with herbaceous species such as Salvadora angustifolia. Carrying capacity for grazers should increase after harvesting as a result of habitat change and grass biomass increase. 10. Total browse production would decrease but leaf biomass should increase on remaining trees as they have improved water availability due to Q lack of intra­ specific competition. Higher seed production and more flowering takes place at lower tree densities. Greatest advantages for browsers after harvesting, is the fact that leaves become senescent later in autumn and that spring leaf flush takes place earlier thus prolonging bro\'se availability.

AFRIKAANSE OPSOMMING:Die hoof doelwitte van hierdie studie was om te bepaal wat die invloed van die oes van mop nie op die ekologie sou wees as dit op 'n volgehoue basis plaasvind en tot w•atter mate mopanie geskik is vir hou skoolvervaardiging. Die navorsing is op die Venetia Limpopo Natuureservaat in slegs drie van die belangrikste mopanie veldtipes uitgevoer met die oorgrote meerderheid van die navorsing in die C.mopane bosveld. Die resultate van die studie kan soos volg opgesom word: 1. Colophospermum mopane is alomteenwoordig op die VLNR. 2. Die C.mopane bosveld het die hoogste digtheid van al drie veldtipes en word ook geassosieer met sekere grondtipes (OaB, VaB, Du, SwB & VaA) wat eie is aan hierdie spesifieke veldtipe. Daar blyk 'n korrelasie te wees tussen die digthede van mopanie en grondtipes. 3. Die grootste mopanie borne, ten opsigte van hnogte en omtrek, word in die C.mopane/C.apiculatum oop bosveld aangetref. Daar is nie 'n beduidende verskil tussen die hoogte en omtrek van mopanie op die verskillende grondtipes nie. 4. Die C.mopane struikveld toon die meeste seniliteit ten opsigte van die persentasie kruin dood. Daar is 'n definitiewe aanduiding dat seniliteit ooreenstem met sekere grondtipes veral met betrekking tot die mopanie struikveld. 5. Die C.mopane bosveld het gemiddeld die oudste borne terwyl die C.mopane/C.apiculatum oop bosveld die vinnigste groeikoers toon. Die bogenoemde feite het 'n ver0and met die grondtipes. 6. Daar is 'n posltiewe korrelasie tussen die totale gewig en die houtskoolgewig van mopanle. Die S\vaarste borne is in die C.mopane!C.apiculatum oop bosveld aangetref, terwyl die swaarste gewig per hektaar in die C.mopane bosveld aangetref is. Gewig kon nie met grondt pes gekorreleer word nie. 7. Die mopanie in die C.mopane bosveld is geskik vir die oes vir houtskool, veral in die Endora, Lizzulea en Hilda gebiede. Dit is raadsaam om die borne in verlengde stroke per hand af te kap (vergroot die ekotoongebied), veral waar arbeid goedkoop is. 'n Oesstrategie van tussen 25% en 50% vir mopanie word aanbeveel om dit ekonomies en ekologies aanvaarbaar te maak. 'n Optimum oesstrategie van 27% word aanbeveel deur 'n oes model wat spesifiak vir hierdie mopane data opgestel is. 8. Daar kan verwag word dat na die oes van mopanie die getalle asook verspreidingspatrone van alle hoefdierspesies kan verander. 'n Voordeel van lae mopanie digthede is dat die verspreiding van die blaarbiomassa ewerediger oor die seisoene sal geskied. Grasvreters word bevoordeel vanwee die verandering in habitat. Die effek van geraas en ander oesbedrywighede op olifante behoort klein te wees aangesien jagaktiwiteite alreeds op diereservaat toegepas word en hulle redelik gewoond daaraan behoort te wees. 9. Grasproduksie behoort toe te neem terwyl die kwaliteit daarvan afneem as gevolg van opportunistieslae kwaliteit grasspcsies wat toeneem na die oes van mopanie, veral as die grand tydens oesaktiwiteite versteur word. Die beste kwaliteit gras word in assosiasie met kruidagtige spesies, veral Salvadora angustifolia, gevi.nd. As gevolg van die verandering in habitat asook die toename in grasbiomassa neem die drakrag vir grasvreters na die oes an mopanietoe. 10. Di.e totale blaarbi.)massa behoort na die oes van mopanie af te neem, maar behoort terselfdertyd op die oorblywende borne as gevolg van die afname in kompetisie vi= watr en anrler natuurlike hulpbronne toe te neem. Hoer persentasies blomvorming en saadproduksie vind by laer boomdigthede plaas. Die grootste enkele voordeel vir blaarvreters, na die oes van mopanie, is die feit dat die blare later in die herfs afval en vroeer in die lente uitbot en dus die voedselbeskikbaarheid vir blaarvreters verleng.

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