Understanding the system and supply chain effects of two residue management treatments in pine and eucalyptus plantations

Thesis (MSc) -- Stellenbosch University, 2022.

ENGLISH ABSTRACT: There is an increased interest in understanding the effect of different residue management practices on forestry in South Africa. In addition to clearly established environmental benefits of residue mulching, as opposed to burning residues in-situ, as mulching or mastication offers the alternative of comminuting these residues almost immediately after harvesting. The aim of this study was to investigate the cost of mulching and determine whether this cost is justified through potential savings from increased pitting and planting productivity in the forestry value chain. Relevant data was collected from sites in Zululand and Bulwer in KwaZulu-Natal and Jessievale on the Mpumalanga Highveld. The study was limited to Eucalyptus grandis x urophylla pulpwood and Pinus patula pulpwood and sawtimber regimes. The study included estimating residual biomass and remaining stump volumes using a Zigzag and Line-Intercept methods respectively. Time studies quantified time consumption and the productivities of the various mulching machines, mechanised pitters, semi-mechanised planters, manual pitters, and manual planters, between treatments. An attempt to classify mulch quality was investigated. The costs of each operation per residue treatment were calculated to determine cost effectiveness. Initial plant growth response to mulched and burnt residues were evaluated. Mulching results for pulpwood residues showed no significant difference between Eucalyptus sites (0.35 ha) and pine sites (0.36 ha PMH-1) and were also not affected by residual biomass volume. Significant differences were found in Eucalyptus mechanised pitting productivity between mulched (0.26 ha PMH-1) and burnt (0.25 ha PMH-1) treatments. Mechanised pitting on sawtimber pine stands differed significantly with a 24% increase in productivity after mulching. Productivities of 0.57 ha PMH-1 and 0.46 ha PMH-1 on mulched and burnt pine sawtimber residues respectively were seen. Manual pitting was more productive for burnt sites (0.06 ha PPH-1) than mulched sites (0.05 ha PMH-1). Semi-mechanised planting was 27% faster on mulched sites (1.70 ha·PMH-1) than on burnt sites (1.33 ha PMH-1). Manual pine planting after mulching was 33% faster compared to planting on burnt sites. This resulted in a manual planting productivity on mulched sites of 0.08 ha PPTH-1 being greater than on sites where residues were burnt (0.06 ha PPTH-1). In both pine and eucalypts, increases in productivities in mechanised pitting, semi-mechanised planting, and manual planting (except manual pitting) after mulching were evident. The total cost of mulching was approximately R 5 450 ha-1 for eucalyptus sites and R 6 170 ha-1 in pine pulpwood sites. The increase in pitting and planting productivity after mulching approximately offsets the mulching cost by R 220 ha-1 on eucalyptus and R 290 ha-1 in pine pulpwood. These saving in increase productivity after mulching are however not enough to justify the expense of mulching generally. When considering mulching foresters should holistic approach the undertaking by considering the biological advantages of mulching in general including soil nutrients benefit as well as long term growth and yield gains, in addition to the increase in productivity of pitting and planting after mulching.

AFRIKAANS OPSOMMING: Daar is tans groot belangstelling om die effek van verskillende reste bestuurspraktyke in die bosbedryf in Suid-Afrika te verstaan. Benewens duidelik bekende omgewingsvoordele van reste-deklaag bewerking, in teenstelling met die brand van reste in opstande, bied deklaag bewerking 'n geskikte alternatief deur hierdie reste feitlik onmiddellik na inoesting te behandel. Die doel van hierdie studie was om die koste van deklaag bewerking te ondersoek en te bepaal of hierdie koste geregverdig is in die bosbou-waardeketting deur potensiële verhogings in groei produktiwiteit. Die nodige data is ingesamel in Zoeloeland en ook Bulwer in KwaZulu-Natal asook Jessievale op die Mpumalanga Hoëveld. Die studie was beperk tot Eucalyptus grandis x urophylla (gom) pulphout en Pinus patula (denne) pulphout en saaghout bestuurspraktykke. Die studie het die skatting van reste massa en oorblywende stomp volumes ingesluit deur gebruik te maak van onderskeidelik ʼn Z-patroon en lyn afsnit opname metode. Tydstudie het tydverbruik en die produktiwiteit tussen behandelings van die verskillende deklaag masjiene, gemeganiseerde gat makers, semi-gemeganiseerde planters, gat maak met die hand en plant met die hand bepaal. Daar is ook gepoog om deklaag kwaliteit te klassifiseer. Die koste van elke operasie van reste behandeling is bereken om kostedoeltreffendheid te bepaal. Aanvanklike groei uitkomste op onderskeidelik deklaag en gebrande reste is gemeet. Deklaag resultate vir pulphout reste het geen beduidende verskil tussen gom persele (0.35 ha PMH-1) en denne persele (0.36 ha PMH-1) getoon nie en is ook nie deur reste volume beïnvloed nie. Beduidende verskille is gevind in produktiwiteit van gemeganiseerde gate maak, tussen deklaag (0.26 ha PMH-1) en gebrande (0.25 ha PMH-1) behandelings in gomme. Gemeganiseerde gate maak by denne saaghout persele het aansienlik verskil, met 'n 24% toename in produktiwiteit na deklaag bewerking. Produktiwiteit van 0.57 ha PMH-1 en 0.46 ha PMH-1 op onderskeidelik deklaag- en gebrande reste in denne saaghout persele is opgemerk. Gate maak met die hand was meer produktief vir gebrande persele (0.06 ha PPH-1) as deklaag persele (0.05 ha PMH-1). Semi-gemeganiseerde plant bewerking was 27% vinniger op deklaag persele (1.70 ha·PMH-1) as op gebrande persele (1.33 ha PMH-1). Plant van denne saailinge en gate maak met die hand na deklaag bewerking was 33% vinniger in vergelyking met plant op gebrande persele. Dit het daartoe gelei dat produktiwiteit op deklaag persele van 0.08 ha PPTH-1 groter was as op gebrande persele (0.06 ha PPTH-1) wanneer met die hand geplant is.. Met vestiging van beide denne- en gom saailinge was verhogings in produktiwiteit in gemeganiseerde gate maak, semi-gemeganiseerde plant en plant-met-hand, behalwe in die geval van gate maak met die hand, na deklaag bewerking duidelik sigbaar. Die totale koste van deklaag bewerking was ongeveer R5 450 ha-1 vir gom persele en R 6 170 ha-1 in denne pulphout persele. Die toename by handgemaakte gate en plant produktiwiteit na deklaag bewerking verminder die deklaag koste met ongeveer R 220 ha-1 in gom pulphout en R 290 ha-1 in denne pulphout. Die verhoogde produktiwiteit en besparing met deklaag bewerking is egter nie genoeg om die koste van deklaag bewerking oor die algemeen te regverdig nie. By die oorweging van deklaag bewerking moet bosbouers die onderneming in geheel benader deur die biologiese voordele van deklaag bewerking, grondvrugbaarheid voordele sowel as langtermyn groei- en opbrengs winste, in konteks met die toename in produktiwiteit van gate maak en plant na deklaag bewerking oorweeg.

Masters