Fruiting and seed production of producer and poor-producer baobab trees and on different land use types in Northern Venda, South Africa
Nangolo, Ester Magano
In southern Africa, the baobab (Adansonia digitata L.) is an economically important trees because it contributes significantly to the livelihoods of local people, particularly in northern Limpopo in South Africa (the southern-most edge of the baobab distribution). All parts of the baobab are useful and considered important for subsistence and commercial uses. Understanding factors that affect fruit and seed production is important to better characterize the long-term success of tree populations. Some adult baobab trees have high fruit production (50 −299 fruits per tree, per year) and are subsequently called ‘producers’ or ‘female’ trees, while there are other trees that produce fewer fruits (< 5 fruits per tree, per year) that are called ‘poor-producers’ or ‘male’ trees. For this study, baobab fruit dimensions (mass, length, volume and ratio) were, measured and compared between artificially- and naturally-pollinated producer and poor-producer trees. Fruit dimensions were also correlated to the number of seeds per fruit. Using 2D geometric morphometric analysis, baobab fruit shapes were analyzed and compared to determine if fruit shape differs between fruits formed on producer and poor-producer baobab trees. I found no significant difference in fruit shape between producer and poor-producer baobab trees. Although, artificially-pollinated trees produced bigger and more uniform shaped fruits and contained more seeds in comparison to the smaller unevenly shaped fruits produced by naturally-pollinated trees. Furthermore, I compared fruit and seed production between naturally-pollinated producer/poor-producer and between artificially-pollinated producer/poor-producer trees that occur on different land use types (i.e. nature reserves, rocky outcrops, plains, fields (land use for agricultural purposes) and villages) in Northern Venda, South Africa. There was a significant difference in fruit and seed production between naturally and artificially-pollinated producer and poor producer trees that occur on different land use types. On average, producer trees yielded more seeds than poor-producer trees. The highest fruit and seed production was recorded in fields and villages. Seed mass variation also differed significantly between producer and poor-producer trees and between the different land use types. A very weak negative relationship between baobab seed number and mass was found in both producer and poor-producer baobab trees. Baobab seed viability was estimated using a 0.1% tetrazolium solution, 100% viability was found in all tested seeds from both producer and poor-producer baobab trees. Result of this study may aid with the identification of land use types where baobabs have the lowest seed production and therefore require additional conservation effort to ensure that fruits are harvested sustainably. The estimation of seed production may improve the ability to estimate the total seed oil that is available in each land use type.
A research report submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the Degree of Masters of Environmental Sciences by Coursework and Research Report. Johannesburg 24 March 2016
Nangolo, Ester Magano (2016) Fruiting and seed production of producer and poor-producer baobab trees and on different land use types in Northern Venda, South Africa, University of Witwatersrand, Johannesburg, < http://wiredspace.wits.ac.za/handle/10539/21065