Selected key ecosystem services, functions, and the relationship with biodiversity in natural forest ecosystems

Mensah, Sylvanus (2016-12)

Thesis (PhDFor)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Ecosystem services (ES) are the benefits people obtain from ecosystems. Biodiversity is a relevant component in this context, as it supports most ecosystem functions. The worldwide decline in natural ecosystem biodiversity and degradation of ecosystems will likely limit the opportunities to improve the services provided if an explicit focus is not put on their maintenance and improvement in future management decisions. This thesis aims at contributing to the knowledge base of ES provision and its relation with biodiversity in South African Mistbelt forests. First, a socio-empirical study was conducted with households from different localities in Limpopo province to assess the relative importance and use of ES by local population. Questionnaires, descriptive rank analysis, logistic regressions and Poisson mixed effect models were used. Results revealed that provisioning and supporting ES (timber and firewood, edible plants and honey) were the most important, and that age, gender, income as well as prior recreational experiences played important roles in respondents’ perceptions. “Timber and firewood” and “honey” were selected for further investigation in Mistbelt natural forests in Limpopo. Second, the potential of Mistbelt forests as foraging habitat for managed honey bees, and as tree biomass and carbon sinks was investigated. Forest inventory was conducted to collect data on woody plant species (plant density, diameter, total height, pollen and nectar values of honey bee plant species; branch and wood core samples, leaf area, plant maximum height). The diversity of honey bee plant species, temporal availability of honey bee forage and relationship of plant diversity with forage production, were explored, using descriptive analysis and general linear models. As results, 48% of the woody plant species recorded in the inventory were honey bee plant species. The highest potential of forage supply was observed during the last quarter of the year. Bee plant species richness, not overall plant richness, showed the greater effect on forage provision. New multispecies biomass models were established and used to estimate aboveground biomass and carbon stocks, and examine the relationship of aboveground carbon with tree species diversity and structural variables. Allometric models with “DBH2xH” were the best fitting. Biomass and carbon stand values of 358.1 Mg ha-1 and 179.0 Mg ha-1, respectively, were obtained. Basal area of most important species, and of largest trees, as well as plant richness were positively correlated with carbon stock. The relationship of biomass and carbon stock with biodiversity components was the final focus. An analysis scrutinised the effects of taxonomic diversity on carbon storage. Correlations were explored through functional traits-based diversity and dominance, using structural equation and linear mixed-effects models. Results showed that taxonomic diversity effects on carbon stock were positive, and mediated by functional diversity and functional dominance. The effects, however, were greater for functional diversity than for functional dominance. In sum, a novel contribution was made to the ES provision of South African Mistbelt forests, which provides a base for the assessment of these forests and their contribution and underpins the need to protect these ecosystems as a natural heritage.

AFRIKAANSE OPSOMMING: Ekostelsel dienste (ED) is voordele vir menselike gebruik wat verkry word uit ekostelsels. In hierdie konteks, is biodiversiteit ʼn relevante komponent, aangesien dit ondersteuning verleen aan verskeie ekostelseldienste. Die wêreldwye afname in natuurlike- ekostelsel biodiversiteit en die agteruitgang van ekostelsels sal moontlik die geleenthede beperk om die dienste te verbeter, indien instandhouding en verbetering nie ʼn prioriteit is in toekomstige bestuursbesluite nie. Die doel van hierdie tesis is om ʼn bydra te lewer tot die basiese kennis van ED voorsiening en die verwantskap tussen ED en biodiversiteit in Suid-Afrikaanse Afromontaan woude. Eerstens is ʼn sosio-empiriese studie uitgevoer onder plaaslike huishoudings verspreid oor die Limpopo provinsie om die behoefte en gebruik van ED deur die bevolking te assesseer. Daar is van vraelyste, ʼn beskrywende rangontleding, logistiese regressie en Poisson-gemengde-effek modelle gebruik gemaak. Die resultate het getoon dat die voorsienende-en ondersteunende-ED (hout en vuurmaakhout, eetbare plante en heuning) die belangrikste was en dat ouderdom, geslag, inkomste en vorige ervarings ʼn belangrike rol gespeel het in die respondente se terugvoer. Die “hout en vuurmaakhout” en “heuning” veranderlikes is gekies vir verdere ondersoek. Tweedens is daar ondersoek ingestel om die potensiaal van Misgordel woude om byeplase van voeding te voorsien te evalueer, asook die potensiaal vir die gebruik van Misgordel woude as ʼn bron van boom biomassa en die vermoë van die woud om as ʼn koolstofstoor op te berg. Bosopmetings is uitgevoer op houtagtige plantspesies om die volgende inligting te bekom: plantdigtheid, boomdeursnee, totale hoogte, stuifmeel en nektar waardes vir heuningby plantspesies; tak en kernhout monsters, blaaroppervlakte en maksimum plant hoogte. Die diversiteit van plant spesies wat deur bye benut word, tydelike beskikbaarheid van heuningby voer en die verhouding tussen plantdiversiteit en voerproduksie is ondersoek. Lineêre modelle en beskrywende statistiek is gebruik. Resultate het getoon dat 48% van die opgetekende houtagtige plant spesies deur bye benut word. Die grootste voerpotensiaal was tydens die laaste kwartaal van die jaar waargeneem. Nuut geformuleerde multispesie biomassa modelle is gebruik om die bogrondse biomassa en koolstofvoorraade te bereken, asook om die verhouding tussen bogrondse koolstof opberging met boomspesie diversiteit en strukturele veranderlikes te ondersoek. Allometriese modelle met “DBH2xH” was die mees geskikte modelle. Waardes vir biomassa en koolstofinhoud van die opstand was 358.1 Mg ha-1 en 179.0 Mg ha-1 onderskeidelik. Die basale-oppervlakte van die belangrikste en die grootste bome, asook plant spesie diversiteit het positief gekorreleer met die koolstofvoorraade. Laastens is die verhouding tussen biomassa en koolstofvoorraade met die biodiversiteit komponente ondersoek. Korrelasies is ondersoek deur die integrasie van funksionele diversiteit en dominansie in strukturele en lineêre gemengde-effek-modelle. Resultate het bewys dat die effek van taksonomiese diversiteit op die koolstofstoorvermoë positief is en dat dit deur funksionele diversiteit en funksionele dominansie bepaal word. Die effekte was meer beduidend vir funksionele diversiteit. Ten slotte, is ʼn nuwe bydrae gemaak tot die voorsiening van ED in Afromontaan woude. Dit dien as ʼn basis vir die assessering van hierdie woude en hulle bydrae, en dit ondersteun die noodsaaklikheid om hierdie ekostelsels as ʼn natuurlike erfenis te beskerm.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100256
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