Estimation of tree biomass, measurement uncertainties, and morphological topology of Androstachys Johnsonii prain

Magalhaes, Tarquinio Mateus (2016-03)

Thesis (PhD (For))--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: This research was aimed at estimating biomass stocks separated in above- and belowground tree components, and studying the topology of the shoot and root systems of Androstachys johnsonnii Prain in woodlands in Mozambique. A two-phase sampling design was used to determine above- and belowground biomass. In the first phase 3574 trees were measured in 23 randomly located circular plots (20-m radius). In the second phase, 93 trees were randomly selected as a subsample from the first phase sample for destructive measurement of biomass and stem volume, along with the variables of the first phase and for topological analysis of the shoot and root systems. Estimates of biomass stocks and quantification of the errors associated with those estimates were obtained using Phase-1 data and regression models. Additionally, biomass expansion factors (BEFs) were fitted based on the 93 trees harvested in the second phase. The estimated total tree forest biomass was 167.05 Mg ha–1 using biomass models and 150.74 Mg ha–1 using BEFs. The percent error resulting from plot selection and biomass regression equations for whole tree biomass stock was 4.55% and 1.53%, respectively, yielding a total error of 4.80%. Among individual variables in the first sampling phase, diameter at breast height (DBH) measurement was the largest source of error. Tree-height estimates contributed substantially to the error as well. For the second sampling phase, DBH measurements were the largest source of error, followed by height measurements and stem-wood density estimates. Of the total error (total variance) of the sampling process, 90% was attributed to plot selection and 10% to the biomass model. The BEF values of tree components were unrelated or weakly related to tree size, and root-to-shoot ratio (R/S) was independent of tree size; therefore, for A. johnsonii, constant component BEF and R/S values can be applied within the interval of sampled tree sizes. Visual analysis indicated herringbone-like branching pattern for both the root and shoot systems. However, the topological index (TI) and topological trend (TT) suggested otherwise. This discrepancy was attributed to the fact that A. johnsonii has multiple laterals per stem/taproot node, suggesting that the topological indexes (TI and TT) might yield biased conclusions regarding the branching pattern when the main axis has multiple laterals per node. Hence, a modified topological index (TIM) was developed that could be applied in the cases of multiple laterals per node while conserving the values of TI for cases with one lateral per node; the modified index was more efficient and realistic than TI. The area preserving branching was confirmed for each stem node confirming the self-similar branching. For the root system, the area-preserving branching was only confirmed for the first node; therefore, self-similarity was not confirmed.

AFRIKAANSE OPSOMMING: Hierdie navorsing was daarop gemik om die biomassa van Androstachys johnsonnii Prain (geskei in bo- en ondergrondse boom komponente) te skat en om die topologie van die loot- en wortelstelsels van hierdie boom in die bosland van Mosambiek te bestudeer. Twee-fase steekproefneming is gebruik om bo- en ondergrondse biomassa te bepaal. In die eerste fase is 3574 bome gemeet in 23 lukraak geleë sirkelvormige persele (20 m radius). In die tweede fase is ’n stel van 93 bome lukraak gekies vanuit die Fase 1 monster, en hierdie stel is gebruik vir destruktiewe meting van biomassa en stamvolume. Die gekose stel het ook die inligting bevat van alle veranderlikes wat in Fase 1 bemoster is plus topologiese ontledings van die loot- en wortelstelsels. Fase 1 data en regressie modelle is gebruik om die biomassa van die bos te skat en om die statistiese foute van hierdie beramings te bepaal. Verder is ʼn biomassa opskalings faktore (BOFe) bepaal vanaf die data van die 93 bome wat in Fase 2 ingeoes is. Die totale biomassa van die bos is geskat op 167,05 Mg ha-1 met behulp van biomassa modelle en op 150,74 Mg ha-1 met behulp die BOFe. Die persentasie fout as gevolg van perseel seleksie en biomassa regressievergelykings vir die totale boom biomassa was onderskeidelik 4,55% en 1,53%, wat gelei het tot 'n totale fout van 4,80%. Onder individuele veranderlikes in Fase 1, was deursnee op bors hoogte (DBH) metings die grootste bron van statistiese foute. Boomhoogte metings het ook aansienlik bygedra tot die fout. Vir die tweede bemonsteringsfase was DBH metings die grootste bron van statistiese foute, gevolg deur hoogte metings en digtheidsbepalings van die stamhout. Van die totale variansie van die monsternemingsproses is 90% toegeskryf aan monsterperseel seleksie en 10% aan die biomassa modelle. Die BOF waardes van boom komponente hou glad nie verband nie (of hou swak verband) met boomgrootte, en die ondergrondse:bogrondse biomassa (O/B) waarde was ook onafhanklik van boomgrootte. Vir hierdie rede kan BOF en O/B waardes vir A. johnsonii, as ʼn konstante komponent toegepas word binne die interval van bemonsterde boomgroottes. Visuele analise het ʼn visgraatagtige vertakkingspatroon vir beide die wortel- en takstelsels aangetoon. Die topologiese indeks (TI) en topologiese tendens (TT) dui egter op ʼn ander patroon. Die verskil word toegeskryf aan die feit dat A. johnsonii verskeie laterale vertakkings het vir elke knoop (nodus) van beide die stam en die penwortel. Die moontlikheid bestaan dat die TI en TT resultate bevooroordeelde gevolgtrekkings met betrekking tot die vertakkingspatroon kan oplewer onder hierdie omstandighede. 'n Aangepaste topologiese indeks (ATI) is ontwikkel wat in die geval van veelvuldige vertakkings per knoop toegepas kan word, met behoud van die waardes van die TI vir gevalle met net een tak per knoop. Hierdie gewysigde indeks was meer doeltreffend en realisties as die TI. Die beginsel van behoud van oppervlakte vir elke vertakking is bevestig vir elke knoop in die stam, wat aandui dat hierdie vertakkingspatroon konstant bly. Vir die wortelstelsel is die beginsel van behoud van oppervlakte slegs bevestig vir

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