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Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa
Thesis (MSc)--Stellenbosch University, 2026.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613926070419456 |
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| access_status_str | Open Access |
| author | Venter, Kuno |
| author2 | Drew, David Michael |
| author_browse | Drew, David Michael Venter, Kuno |
| author_facet | Drew, David Michael Venter, Kuno |
| author_sort | Venter, Kuno |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2026. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/135624 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:43:54.041Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/135624 Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa Venter, Kuno Drew, David Michael Germishuizen, Ilaria Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science. Thesis (MSc)--Stellenbosch University, 2026. Venter, K. 2026. Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/7975f1d2-ad3b-4c84-b29a-b0daf787151b Accurate prediction of height growth and site productivity in Eucalyptus grandis plantations has become increasingly important as the forestry sector faces rising climatic variability and long-term shifts in temperature and rainfall regimes. Although numerous growth and yield studies exist for short-rotation pulpwood systems, limited research has focused on long-rotation sawtimber production in South Africa, particularly with respect to climate-sensitive modelling. This study develops and evaluates dynamic, climate-responsive Site Index (SI) and dominant-height models for long-rotation E. grandis in Limpopo province, integrating long-term Permanent Sample Plot (PSP) data with high-resolution climatic datasets to support adaptive plantation management under changing environmental conditions. The study utilised PSP data collected by Merensky Timber across a broad range of altitudes, rainfall regimes, and productivity levels. Dominant height was calculated using the South African standard definition based on the mean height of the thickest 20% of trees. Climatic variables, including CHIRPS rainfall, CHIRTS temperature, potential evapotranspiration (PET), Standardised Precipitation-Evapotranspiration Index (SPEI), and the full suite of BIOCLIM indices, were spatially linked to each plot. Five dynamic height-growth models were fitted using non-linear least squares: Chapman–Richards (HT2CR4), Hossfeld (HT2HF3), Schumacher-type (HT2JC), McDill–Amateis (HT2MA2), and the log-Schumacher (HT2SCH) formulation. Model performance was assessed using separate calibration (70%) and validation (30%) PSP sets, followed by independent blind validation against compartment-level enumeration data. Parameter–climate relationships were quantified using correlation analysis and stepwise AIC model selection, providing the basis for developing climate-modified dynamic height equations. The PSP dataset captured wide variability in dominant height and site productivity, supporting robust model fitting. Across the five dynamic models, HT2MA2 and HT2HF3 achieved the highest predictive accuracy, characterised by low RMSE, minimal bias, and strong biological realism throughout the rotation. The Chapman–Richards and Schumacher-type models showed weaker fit and structural instability at older ages. Climate–parameter linkage analyses revealed strong associations between precipitation seasonality, dry- and wet-season rainfall (e.g., BIO16, BIO17), drought indices (SPEI), and key model parameters, indicating that climatic gradients significantly influence height-growth dynamics in long-rotation E. grandis. Despite clear climate–parameter relationships, the inclusion of additive climate modifiers did not improve model performance. Climate-modified predictions showed increased error and instability, particularly for HT2HF3, which exhibited sensitivity to parameter perturbation. Independent blind validation confirmed that unmodified models consistently outperformed modified versions when applied beyond the PSP calibration dataset. These results highlight the need for more flexible modelling approaches—such as hierarchical, hybrid, or process-informed frameworks—before climate variables can be reliably incorporated into operational height-growth projections. Overall, this study demonstrates that dynamic empirical models, especially HT2MA2 and HT2HF3, provide accurate and stable representations of dominant-height growth for long-rotation E. grandis in Limpopo. While climate clearly shapes height-growth potential, simple additive parameter modifiers are insufficient for operational deployment. The modelling framework developed here establishes a scientifically robust foundation for climate-aware growth forecasting and provides direction for future research into more sophisticated, adaptive modelling strategies. Masters 2026-04-02T10:58:57Z 2026-04-02T10:58:57Z 2026-03 Thesis https://scholar.sun.ac.za/handle/10019.1/135624 en Stellenbosch University 93 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Venter, Kuno Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa |
| title | Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa |
| title_full | Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa |
| title_fullStr | Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa |
| title_full_unstemmed | Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa |
| title_short | Development and testing of climate-sensitive site index models for long rotation Eucalyptus grandis in Limpopo province of South Africa |
| title_sort | development and testing of climate sensitive site index models for long rotation eucalyptus grandis in limpopo province of south africa |
| url | https://scholar.sun.ac.za/handle/10019.1/135624 |
| work_keys_str_mv | AT venterkuno developmentandtestingofclimatesensitivesiteindexmodelsforlongrotationeucalyptusgrandisinlimpopoprovinceofsouthafrica |