- Title
- Long-term impacts of re-establishment practices on pine pulpwood production, South Africa
- Creator
- Ndlovu, Noxolo Nokwethemba
- Subject
- Pulpwood -- South Africa
- Subject
- Forest management -- Environmental aspects Forest management
- Date Issued
- 2019
- Date
- 2019
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10948/41785
- Identifier
- vital:36582
- Description
- Within South Africa, Pinus species (pines) occupy 50.8% of the total commercial plantation forestry area, of which 29.4% is planted for pulpwood production. Intensive re-establishment is practiced to promote pine productivity (tree survival, growth and uniformity). Extensive international and local (South African) research has been conducted to determine the short-term (up to ca. nine years of age) impacts of individual and integrated re-establishment practices on pine productivity. However, there is limited rotation-length data available for pine pulpwood (grown within South Africa) with which to provide an understanding of the full implications of individual and integrated impacts of re-establishment practices on longer-term tree survival, growth and uniformity. Data from these trials could then be used to justify silvicultural inputs (if any) and potentially refine management decision-making for subsequent rotations. Three pine trials were established in 1997/8 on three contrasting sites to test the influence of a range of re-establishment practices, and included site preparation (slash management and preparation of a planting position), fertilisation and vegetation management, and/or any interaction, on short- and long- term pine pulpwood productivity within South Africa. Pinus patula was planted at Blyde and Pinus elliottii at Bergvliet (both situated in Mpumalanga), and Pinus greggii planted at Hlabeni in KwaZulu-Natal. Final measurements were taken at 17 years at Blyde and Bergvliet, with the Hlabeni trial only assessed to age 11.6 years due to premature felling. Measurements of vegetation cover and biomass, soil and foliar nutrients, tree survival, growth and uniformity were used to provide an insight into treatment responses, both within and between sites. At Blyde (Chapter 2), the individual and integrated impact of different practices of slash management (Burn versus No Burn), preparation of a planting position (Pit, Rip, Chopper roll and Pit and Chopper roll and Rip) and vegetation management (Weedfree versus Weedy) were investigated. The vegetation on the site (initially a mixture of grasses, herbaceous broadleaves and woody plants) competed with the seedlings from 0.3 years, with the woody component (mainly Solanum mauritianum and Buddleija salviifolia) remaining competitive through to rotation-end. From 2.5 years there was an interaction between the preparation of a planting position and vegetation management with the lowest vegetation biomass recorded in the Rip + Weedy treatments. Overall soil and foliar magnesium and potassium levels were considered sub-optimal, however this did not translate to rotation-end tree productivity differences. Tree survival was not impacted negatively by any of the main effects, or their interactions. At rotation-end (17 years) slash management (as a main factor) was not significant in terms of tree growth, whereas preparation of a planting position was significant for BA and Vol (Rip > Pitting ~ Chopper roll), and vegetation management (Weedfree > Weedy) for Dbh, BA and Vol. In addition, there was a significant interaction between the preparation of a planting position and vegetation management for BA and Vol, with the need to manage vegetation more critical when pitting, compared to when ripping and/or chopper rolling. At Bergvliet (Chapter 3), the individual and integrated impact of slash management (Clear, Single and Double), fertilisation (Fertilisation versus No Fertilisation) and vegetation management (Weedfree versus Weedy) were investigated. The vegetation on the site (initially a mixture of grasses, herbaceous broadleaves and woody plants) competed with the seedlings from 0.4 years, with the woody component (mainly pine regeneration, Solanum mauritianum and Lantana camara) remaining competitive until rotation-end. Neither slash management nor fertilisation had a notable influence on vegetation cover. At 1.3 years, biomass sampled indicated a relationship between slash management and fertilisation where biomass was highest within the Clear + Fert (4 398 kg ha-1) and Double + No Fert slash treatments (4 698 kg ha-1). Soil and tree foliar nutrients were considered acceptable. At 17 years, vegetation management (Weedfree > Weedy) and the interaction between slash management and fertilisation significantly influenced rotation-end tree survival (Double + No Fert ~ Single + No Fert ~ Clear + Fert ~ Clear + No Fert > Double + Fert ~ Single + Fert). Neither slash management nor fertilisation (as main factors) had a significant influence on rotation-end growth. Vegetation management significantly improved Ht, Dbh, BA and Vol at rotation-end (Weedfree > Weedy). The management of vegetation resulted in 67.5 m3 ha-1 more volume at rotation-end than in the Weedy plots. At Hlabeni (Chapter 4), the individual and integrated impacts of different forms of fertiliser (No Fertilisation, Maxiphos, Agriphos and NPK) and ring weeding distances (0, 1, 2 and 3 m) were tested. Competition occurred from 0.6 years, and was from mainly grasses (and sedges) and herbaceous vegetation with limited woody plants. Fertilisation did not have a notable influence on vegetation cover, nor did it have a significant influence P. greggii survival and growth. However, fertilisation increased the vegetation biomass (NPK > No Fert ~ Agri > Maxi) which indirectly influenced P. greggii uniformity at 11.6 years. During initial stand development P. greggii responded positively (linear) to an increase in the area ring kept free of competitive vegetation (3_m > 2_m > 1_m > 0_m). Positive growth responses to vegetation management were, however, no longer significant at 11.6 years (except for height growth) possibly due to the absence of more suppressive woody plants. The results from these trials indicate that vegetation management was the most important silvicultural practice at re-establishment especially where woody vegetation persists. Results from this trial series confirm current vegetation management practices within South Africa are adequate, where the immediate area around the seedling or tree is kept free of vegetation with control of any woody vegetation that occurs outside of this area. The results also suggest that slash retention is acceptable if pitting and planting are properly undertaken, while fertiliser application did not have any notable benefit. In addition, these trials have indicated the value (to forest managers) of understanding the integrated impacts of silvicultural practices on long-term tree productivity..
- Format
- xiv, 96 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
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