Fruit-based allometry of Strychnos madagascariensis, S. spinosa, and Trichilia emetica in the savanna woodlands of the Umhlabuyalingana municipality, KwaZulu-Natal, South Africa
| dc.contributor.author | Akweni, Arindo Lukawu | |
| dc.date.accessioned | 2023-03-14T10:28:36Z | |
| dc.date.available | 2023-03-14T10:28:36Z | |
| dc.date.issued | 2021 | |
| dc.description | A thesis submitted to the Faculty of Science, Agriculture and Engineering in fulfilment of the requirements for the Degree of Doctor of Philosophy in the Department of Agriculture at the University of Zululand, South Africa, 2021 | en_US |
| dc.description.abstract | Savannah woodlands of South Africa are endowed with a high diversity of fruit tree species among of which are Strychnos madagascariensis, S. spinosa, and Trichilia emetica, which have a potential for commercial harvest from the wild. Assessment of the profitability of harvesting their fruits and as well as informed decisions to harvest their fruits require an estimation or quantification of the yields of the fruits. However, allometric equations that enable the quantification of fruit biomass of trees from the wild are non-existent. The present study had four objectives. The first was to develop fruit based allometric equations for Strychnos madagascariensis and S. spinosa. The second was to determine biomass allocation between fruit components of Strychnos madagascariensis and Strychnos spinosa and to derive the carbon (C) stocks sequestrated by fruits. The third was to evaluate the production potential of the Central Portions of the Umhlabuyalingana Municipality (CPUM) in terms of fruit biomass of Strychnos madagascariensis and S. spinosa. The fourth was to calibrate allometric equations that predict the amount of fruits and the biomass of seeds of T. emetica. Therefore, there were four studies done in accordance with these four objectives. Development of fruit-based allometric equations A total of 80 trees of S. madagascariensis and S. spinosa were selected by applying a stratified sampling approach according to four stem diameter classes during fruit ripening period. For each tree, the following parameters were measured: fruit biomass, diameter at breast height (DBH), canopy diameter, and total height. Six forms of the allometric models were fitted to the data using ordinary least squares method. DBH was the only appropriate variable in the prediction of the fruit biomass and explained 99.9% of the variation in fruit biomass. The simple linear regressions linking the DBH (in cm) to the total fresh fruit biomass (FB; in kg) were the best models and were expressed by (1) FB = 1.0243 × DBH1.1841; and (2) FB = 1.0297 × DBH1.1956; respectively for Strychnos madagascariensis and Strychnos spinosa. Biomass allocation between fruit components and carbon (C) stocks sequestration by fruits A total of 400 ripe fruits of S. madagascariensis and S. spinosa were harvested from trees distributed in seven plots across the UMkhanyakude district. Fruit shell and pulp were separated from seeds. Puree and juice of S. spinosa were separated by centrifugation and steam extraction, respectively. Moisture contents of the fruit components were measured. For S. madagascariensis fruits, seeds contributed the most biomass (50.2 %), followed by the shell (30.8 %), and pulp had the least biomass (16.7 %). The loss of material was 2.3 %. For S. spinosa, the largest part of fruit biomass was in the shell (41.8 %), followed by puree (25.6 %), seeds (18.6 %), juice (6.2 %), and pulp (0.9 %). The loss of material was 6.9 %. Fruit dry biomass (FDB; in g) and fruit carbon stocks (CB; in g) were both related to fruit diameter (D; in cm) for S. madagascariensis (FDB = 1.022 ᵡ D2.492; CB = 0.463 ᵡ D2.539 ) and S. spinosa (FDB = 1.015 ᵡ D2.38; CB = 0.198 ᵡ D2.821). Strychnos madagascariensis and S. spinosa fruit biomass potential of Central Portions of the Umhlabuyalingana Municipality (CPUM) Field surveys of trees of S. madagascariensis and S. spinosa were conducted in eight 0.25-ha square plots following an East-West distance gradient of 1.4 km. The fruit biomass of trees was estimated using the fitted fruit-based allometric equations. ArcGIS tools were used to obtain the global fruit biomass production in the CPUM. The productivity of the CPUM was on average 935.2 ± 532 kg ha-1 and 1211.8 ± 971 kg ha-1 of fresh fruit biomass, respectively for S. madagascariensis and S. spinosa. This represented a maximum production potential of 13192.98 tons (t) and 17095.01 t of fresh fruit biomass for S. madagascariensis and S. spinosa, respectively. Development of allometric equations to predict fruits and seed biomass of T. emetica A total of 35 trees of T. emetica were selected based on seven classes of the diameter at breast height (DBH) in the Umkhanyakude district. Fruits were counted on each tree using randomized branch sampling technique. Twelve fruits were harvested per tree and were brought to the laboratory for the determination of biomass. Linear models, basing solely on DBH (in cm), were the best predictors of both the number of fruits on the trees (NF) and the fresh seed biomass (SB; in kg) of T. emetica. The exponential forms of the best-fit general models were: (1) NF = 375.364 × DBH 1.009; and (2) SB = 1.858 × DBH 1.009 . The prediction tests of these models were not satisfactory. Tree size category models improved accuracy of predictions. The above studies produced allometric equations that make it possible to quantify and predict the fruit yield of S. madagascariensis, S. spinosa, and T. emetica from their tree dimensions. These equations also allowed the derivation of the amount of juice, puree, nectar, or oil from the fruits. Furthermore, they helped to determine the repartition of biomass and carbon stocks within the fruit components. This study proved that, through fruit-based allometric equations, one can evalute the commercial value of savannah woodlands basing on their fruit biomass production potential | en_US |
| dc.description.sponsorship | National Research Foundation | en_US |
| dc.identifier.uri | https://hdl.handle.net/10530/2241 | |
| dc.language.iso | en | en_US |
| dc.publisher | University of Zululand | en_US |
| dc.subject | Strychnos madagascariensis, S. spinosa, savanna woodlands, | en_US |
| dc.title | Fruit-based allometry of Strychnos madagascariensis, S. spinosa, and Trichilia emetica in the savanna woodlands of the Umhlabuyalingana municipality, KwaZulu-Natal, South Africa | en_US |
| dc.type | Thesis | en_US |
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