Drought stress responses in wild and cultivated Aspalathus linearis of the Suid Bokkeveld, Northern Cape Province of South Africa : linkages between local knowledge and empirical evidence

Rafferty, Melandri Crystal Tameron (2018-03)

Thesis (MScConsEcol)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The north-western region of the Western Cape forms part of the Fynbos biome and is home to the indigenous plant, A. linearis (rooibos). Rooibos cultivation is restricted to a small geographic area with wild rooibos plants being more at risk as a result of climate change. This research contributes to a growing body of evidence of the impacts observed and experienced by small-scale farmers, by adding much-needed analysis of empirical data on rooibos under low precipitation conditions to the body of science. The overall aim of this study was to examine the physiological response, using xylem hydraulic conductivity, to drought stress of wild and cultivated A. linearis plants in the Suid Bokkeveld and to determine the effects of organic mulch on cultivated rooibos‘ susceptibility to xylem cavitation in response to drought stress. The information was used to compare farmer perceptions of rooibos drought responses and to spotlight the variations and similarities between the two information systems (scientific and local ecological knowledge) with the hope of providing guidelines for effective climate change adaptation strategies. A. linearis appears to respond to soil moisture gradients but showed little differences within sites according to the reseeder-resprouter dichotomy. On the other hand, the use of mulch did not have an impact on the cultivated rooibos‘ hydraulic characteristics. Cultivated (reseeding) and wild (resprouting) rooibos ecotypes may differ in terms of their physiology, however, when the effects of drought exceed levels of tolerance in the two ecotypes, according to responses from the questionnaire survey, both may exhibit similar strategies (branch sacrifice and red leaf discoloration) to cope with prolonged precipitation deficits. The quarterly climate change workshops have proven to be a helpful tool when it comes to incorporating local climate issues with that of seasonal forecasts and ultimately provides a platform for adapting new methods in addressing the impacts of drought and climate change. Results from the traditional scientific methods and the survey questionnaire on local knowledge show that there may exist important disparities between these two methodologies, however, each prove invaluable for understanding certain phenomena exhibited, in this case, by wild and cultivated rooibos ecotypes. Local knowledge should be used to emphasize problem areas and detect possible solutions whereas conventional scientific methodologies may often assist in converting potential problems into a broader range of appropriate hypothesis testing.

AFRIKAANSE OPSOMMING: Die noordwestelike streek van die Wes-Kaap vorm deel van die Fynbos-bioom en is die tuiste van die inheemse plant, A. linearis (rooibos). Rooibos produksie is beperk tot 'n klein geografiese area en klimaatsverandering hou 'n bedreiging in vir veld rooibos plante. Hierdie navorsing dra by tot die toenemende bewyse rakende die impak wat deur kleinboere waargeneem en ervaar word, deur die noodsaaklike analise van empiriese data aangaande rooibos, onder droogte toestande, by die liggaam van wetenskap te voeg. Die algehele doel van hierdie studie is om die verskillende fisiologiese reaksies op droogtestres van veld en mak A. linearis plante in die Suid-Bokkeveld te ondersoek, deur die gebruik van xileem hidrouliese geleidingsvermoë, en om die effekte van organiese deklaag op die mak rooibos se vatbaarheid tot xileem ―kavitasie‖ in respons tot droogtestres, vas te stel. Die inligting was gebruik om die persepsies van boere aangaande die respons van rooibos plante teenoor droogtestres te vergelyk en om die verskille en ooreenkomste tussen die twee kennisstelsels (Wetenskaplike en Plaaslike Ekologiese Kennis) met die hoop om riglyne te vir effektiewe aanpassingsstrategieë ten opsigte van klimaatsverandering te verskaf. Dit blyk dat A. linearis plante op grondvog gradiënte reageer, maar het min verskille binne elk van die studie plase, volgens die hersaaier-herspruiter-digotomie, getoon. Aan die ander kant het die deklaagbewerking geen impak op die hidrouliese eienskappe gehad nie. Die mak (hersaaier)-, en veld (herspruiter) rooibos-ekotipes mag verskil op grond van hul fisiologie, maar wanneer die uitwerking van droogte egter die toleransievlakke in die twee ekotipes oorskry, mag beide van hierdie ekotipes soortgelyke fisiologiese veranderinge ondergaan, naamlik die verlies van takke en rooi blaarverkleuring (volgens die antwoorde soos gelys in die vraelys opname) ten einde by te hou met verlengde neerslae. Die kwartaallikse werkswinkels rakende klimaatsverandering het bewys dat dit ‗n nuttige hulpmiddel is met betrekking tot die inkorporering van plaaslike klimaatkwessies met dié van seisoenale voorspellings en bied 'n platform vir die aanpassing van nuwe strategieë om die impak van droogte en klimaatsverandering beter te hanteer. Resultate van die tradisionele wetenskaplike metodes en die vraelys-opname oor plaaslike kennis, toon dat daar belangrike verskille tussen hierdie twee metodieke mag bestaan, maar elkeen blyk waardevol te wees ten einde sekere verskynsels te verstaan, in hierdie geval deur veld- en mak rooibos-ekotipes. Plaaslike kennis moet benut word om probleemareas te beklemtoon en moontlike oplossings op te spoor terwyl konvensionele wetenskaplike metodieke kan dikwels bystand bied ten einde potensiële probleme om te skakel in 'n wyer reeks toepaslike hipotese toetsing.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103775
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