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Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning
Thesis (PhDFor)--Stellenbosch University, 2025.
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| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867614115849043968 |
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| access_status_str | Open Access |
| author | Pienaar, Louis Otto |
| author2 | Du Toit, Ben |
| author_browse | Du Toit, Ben Pienaar, Louis Otto |
| author_facet | Du Toit, Ben Pienaar, Louis Otto |
| author_sort | Pienaar, Louis Otto |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhDFor)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132501 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:46:55.034Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132501 Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning Pienaar, Louis Otto Du Toit, Ben Wellstein, Camillia Calama, Raphael Olivar, Jorge Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science. Pinus radiata -- South Africa -- Western Cape -- Boland region Pinus radiata -- Thinning -- Quality control Forest biomass -- Carbon content Carbon sequestration -- Estimates Pinus radiata -- Growth -- Measurement Photosynthesis UCTD Thesis (PhDFor)--Stellenbosch University, 2025. Pienaar, L. O. 2025. Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/ecbf5370-fd07-4940-8ec9-470d8eb891e5 ENGLISH ABSTRACT: Pinus radiata is an important plantation forestry species within the Boland region of Western Cape Province, South Africa, and its management requires accurate information. This study had two main objectives: (a) to develop allometric equations that could accurately estimate biomass and carbon sequestration in various above-ground components, and (b) to determine the growth response, light use efficiency (LUE) and vulnerability of Pinus radiata stands subjected to various thinning types at age 20 years (the time of a scheduled second thinning operation). Thinning types included thinning from above (Ta), thinning from below (Tb) and the control treatment which remained unthinned during this study period. The objectives were met by (1) developing component biomass equations from a two-step upscaling approach from similar stands in the Boland Region, (2) creating models to accurately estimate leaf area index (LAI), (3) determining the growth response and LUE of thinning treatments over wet and dry seasons of two years post treatment, and (4) by providing recommendations for the management of stand vulnerability under adverse climatic conditions (including climate change). Results indicated that the best needle and above ground biomass (AGB) models were those that contained the independent variables diameter at breast height (DBH) and the combined variable DBH2 and total height (H) for needle mass and AGB respectively. LAI could accurately be estimated from models using Ceptometer measurements in combination with stocking. The growth response indicated that there were no significant differences in quadratic mean diameter (Dq) and volume increment between the thinned treatments, but that significant differences existed between the thinned treatments and control with the control treatment having significantly higher volume increment, especially during the second year of the study (a very wet period). There were also seasonal differences in Dq and volume increment between the treatments. Similar trends to the volume increment could be seen for the above ground net primary production (ANPP). Densification or regrowth of the canopy had not taken place since thinning implementation and the LAI remained relatively stable over the duration of the study period. Significant differences were observed in LAI between the thinned treatments and the control. The LUE of the treatments were not significantly different from each other when averaged over the full two-year period since treatment. However, increases in LUE were detected for treatments from the dry to the wet seasons with significant differences observed for the control versus the two thinning treatments during the second year. The slenderness ratio of the control stands measured at the end of the study period indicated that the stands are becoming increasingly unstable, while the relative density has shown that the stands are approaching a stage where tree mortality is imminent. The control treatment has shown superior volume growth in comparison to the thinning treatments. Leaving the control stands unthinned might be tempting, but the stands is becoming increasingly unstable and vulnerable to pest and disease outbreaks and drought. Considering that there were no significant differences in growth response between the Ta and Tb treatments, the decision as to which treatment to implement will be an economical, rather than a biological decision, driven by market demand. AFRIKAANSE OPSOMMING: Pinus radiata is 'n belangrike plantasie-bosbou spesie in die Wes-Kaap Provinsie, Suid-Afrika, en die bestuur daarvan vereis akkurate inligting. Hierdie studie het twee hoofoogmerke gehad: (a) om allometriese vergelykings te ontwikkel wat biomassa en koolstofsekwestrasie in verskeie bogrondse komponente akkuraat kan skat, en (b) om die groeireaksie, liggebruik-doeltreffendheid (LGD) en kwesbaarheid van ‘n middel-/kort-rotasie Pinus radiata-opstand wat aan verskillende dunningsbehandelings onderwerp is, te bepaal. Dunningsbehandelings het dunning van bo (Db), dunning van onder (Do) of geen dunning as 'n kontrolebehandeling ingesluit. Die doelwitte is bereik deur (1) die ontwikkeling van komponent-biomassa-vergelykings uit 'n tweeledige opskaalbenadering van soortgelyke opstand in die Boland-streek, (2) die skep van modelle om blaaroppervlakte-indeks (BOI) akkuraat te skat, (3) die bepaling van die groeireaksie en LGD van dunningsbehandelings oor nat en droë seisoene vir twee jaar na behandeling, en (4) deur aanbevelings te maak om die opstand se kwesbaarheid in die aanwesigheid van klimaatsverandering te bestuur. Resultate het aangedui dat die beste naald- en bogrondse biomassa (BGB)-modelle samgestel kon word met die onafhanklike veranderlikes borshoogte-deursnee (BD) en die gekombineerde veranderlike BD² en totale hoogte (H), ten einde vir naaldmassa en BGB onderskeidelikte skat. BOI kon akkuraat geskat word uit modelle wat Ceptometer-metings in kombinasie met opstandsdigtheid gebruik. Die groeireaksie het aangedui dat daar geen beduidende verskille in kwadratiese gemiddelde deursnee (KGD) en volume aanwas tussen die gedunde behandelings was nie, maar dat daar beduidende verskille tussen die gedunde behandelings en kontrole was, met die kontrolebehandeling wat 'n beduidend hoër volume aanwas gehad het, veral gedurende die tweede jaar van die studie ('n baie nat periode). Daar was ook seisoenale verskille in KGD en volume aanwas tussen die behandelings. Soortgelyke tendense as die volume aanwas kon gesien word vir die bogrondse netto primêre produksie. Verdigting of hergroei van die kroon het nie plaasgevind sedert die implementering van dunning nie en die BOI het relatief stabiel gebly gedurende die studieperiode. Beduidende verskille is waargeneem in BOI tussen die gedunde behandelings en die kontrole. Die LGD van die behandelings was nie beduidend verskillend van mekaar wanneer die gemiddelde van die behandelings oor die volle twee jaar vergelyk was nie. Daar kon egter verhogings in LGD gesien word vir behandelinge van die droë na die nat seisoene, met beduidende verskille waargeneem vir die kontrole versus die twee dunningsbehandelings gedurende die tweede jaar. Die slankheidsverhouding van die kontrole-opstand wat aan die einde van die studieperiode gemeet is, het aangedui dat die opstand toenemend onstabiel word, terwyl die relatiewe digtheid getoon het dat die opstand 'n stadium bereik waar boommortaliteit onmiddellik kan plaasvind. Die kontrolebehandeling het sterk volume-groei getoon in vergelyking met die dunningsbehandelings. Om die kontrole-opstand ongedund te laat, mag aanloklik voorkom, maar die opstand word toenemend onstabiel en kwesbaar vir plaag- en siekte uitbrake, asook droogte. Aangesien daar geen beduidende verskille in groeireaksie tussen die Db- en Do-behandelings was nie, sal die besluit oor watter behandeling geïmplementeer moet word 'n ekonomiese, eerder as 'n biologiese besluit wees, gedryf deur marknavraag. Doctoral 2025-06-10T07:40:45Z 2025-06-10T07:40:45Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132501 en Stellenbosch University xii, 97 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Pinus radiata -- South Africa -- Western Cape -- Boland region Pinus radiata -- Thinning -- Quality control Forest biomass -- Carbon content Carbon sequestration -- Estimates Pinus radiata -- Growth -- Measurement Photosynthesis UCTD Pienaar, Louis Otto Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning |
| title | Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning |
| title_full | Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning |
| title_fullStr | Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning |
| title_full_unstemmed | Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning |
| title_short | Biomass determination, growth response and light use efficiency of mid-rotation Pinus radiata stands, post thinning |
| title_sort | biomass determination growth response and light use efficiency of mid rotation pinus radiata stands post thinning |
| topic | Pinus radiata -- South Africa -- Western Cape -- Boland region Pinus radiata -- Thinning -- Quality control Forest biomass -- Carbon content Carbon sequestration -- Estimates Pinus radiata -- Growth -- Measurement Photosynthesis UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132501 |
| work_keys_str_mv | AT pienaarlouisotto biomassdeterminationgrowthresponseandlightuseefficiencyofmidrotationpinusradiatastandspostthinning |