Methods of assessing utilisable sawlog volume of riparian alien invasive forests in the Western Cape Province of South Africa

Marais, Brendan Nicholas (2018-03)

Thesis (MScFor)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Alien invasive plant (AIP) species pose a significant threat to biodiversity, water security and agricultural resources. Several river courses in the Western Cape province of South Africa experience a severe problem with AIPs. Working for Water, a government initiative established in 1995 (now part of the Department of Environmental Affairs [DEA] under Natural Resources Management [NRM]), has identified the Berg River as particularly problematic with biomass ear‐marked for clearing. To date, NRM has cleared nearly 3 million hectares of AIPs and creates 20 000 jobs per annum. The Value‐Added Industries (VAI) Programme has been created in an attempt to extract value from cleared biomass instead of leaving it in‐field. This study presents an inventory of riparian alien invasive forests (AIFs) focussing on a method of measuring utilisable sawlog volume for the production of wooden school desks. The results of the sawlog inventory are presented with a type of correction factor, correcting for measured decreases in utilisable volume resulting from deviant stem form. The correction factor is a comparison between conventionally derived standing volume and more in‐depth measurements of tree‐level variables for estimates of higher value sawlogs over five diameter classes at breast height (DBH) classes, for two AIP species (Eucalyptus camaldulensis and Acacia mearnsii) present on the study site. Stem height at first major branching was measured and assessed in the first step of determining the correction factor. Thereafter, stem taper was assessed by measuring diameter at breast height and upper stem diameter at first major branching. This was compared to conventional equations used to derive upper stem diameter at first major branching for a tree of given DBH. Lastly, stem sweep was measured and assessed. The Simsaw 6 software package was used to conduct sawing simulations to acquire insight into the possible range of sawn product volume recovery attainable from AIFs as well as in the creation of the so called sawlog volume creation factor (SVCF) through the input of sawlog dimensions and subsequent volume calculation thereof. The results showed that height at first major branching influenced sawlog volume recoverable from the AIF site with stem taper not featuring as a variable of interest. Furthermore, the presence of stem sweep influenced sawn product volume recovery compared to logs with no sweep. The results of this study are expected to feed into NRM’s Management Unit Clearing Plan (MUCP); software developed for the purposes of visualising the extent of invasion density and the subsequent operations and costs thereof required to clear areas of AIPs completely.

AFRIKAANSE OPSOMMING: Uitheemse indringer plant spesies (AIP) veroorsaak ‘n beduidende bedreiging vir biodiversiteit, watersekerheid en landbou hulpbronne. Verskeie rivierlope in the Wes Kaap Provinsie in Suid Afrika ondervind tans erge probleme met indringer plante. Werk vir Water (Working for Water), ‘n staatsprogram, gevestig in 1995, wat nou deel uitmaak van Departement van Omgewingsake (DEA) en tans resorteer onder Natuurlike Hulpbronne Bestuur (NRM), het die Bergrivier geïndentifiseer as uiters problematies met heelwat biomassa wat verwyder moet word. Tot op hede is bykans 3 miljoen hektaar indringer plante verwyder deur NRM en skep hierdie projek ongeveer 20 000 werksgeleenthede per jaar. Die Toegevoegde Waarde Industriële Program, (VAI Programme) is geskep in ‘n poging om waarde uit hierdie uitgekapte biomassa te haal instede daarvan om dit op‐veld agter te laat. Hierdie navorsing studie bied ‘n opsomming van rivierlangs uitheemse indringer bos met die fokus op die metodiek van meting van bruikbare saag volumes wat aangewend kan word om skoolbanke te produseer. Die resultate van die bruikbare saag volumes word voorgele met ‘n regstellende faktor (correction factor), die resultaat van verminderende volumes bruikbare hout weens kromgetrekte stamme. Die regstellende faktor is wiskundig bepaal na aanleiding van die vergelyking van konventionele geplante volumes teenoor meer spesifieke meting van boom‐vlak variasies vir skattings van hoe‐waarde saag volumes oor 5 diameter klasse op borshoogte (DBH). Gemeet vir twee AIP spesies, naamlik, Eucalyptus camaldulensis and Acacia mearnsii wat op die ondersoek terrein voorkom. Stamhoogte by die eerste vertakking was gemeet en ge‐evalueer as die eerste stap in die bepaling van die regstellende faktor. Daarna is stamspitsing (taper) bepaal deur meting van DBH en dan die boonste stamdiameter by eerste hoofvertakking. Hierdie waardes is dan vergelyk met normale berekeninge om boonste stamdiameters op eerste hoofvertakkings te bereken vir bome met gegewe DBH. Laastens is stamkurwe gemeet en ge‐evalueer. Die Simsaw 6 sagteware is aangewend om saagmeul simulasie te doen om der halwe resultate te lewer oor moontlike gesaagte produk volumes wat bekom sal word van AIFs. Dit het ook tot die skep van die genoemde “sawlog volume correction factor” (SVCF) of te wel “saagblok volume regstellende faktor” [SVRF] gelei na aanleiding van saagblok mates en afgeleide volume berekeninge wat daaruit gevloei het. Die resultate toon dat hoogte op eerste hoof vertakking wel ‘n invloed het op saagblok volumes wat herwin word van AIFs terwyl stamspitting minimale invloed het op finale resultate. Verder is gevind dat aanwesigheid van stamkurwe die finale volumes negatief be‐ïnvloed teenoor stamme met geen kurwes. Die resultate van hierdie ondersoek behoort deel te vorm van NRM se toekomstige “Management Unit Clearing Plan” (MUCP); die ontwikkelde sagteware wat ten doel het om te help met visualisering van indringer digtheid en sal bydra tot koste‐bepaling van skoonmaak operasies wat benodig word om AIPs totaal te verwyder.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103928
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