Department of Conservation Ecology and Entomology

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Browsing Department of Conservation Ecology and Entomology by browse.metadata.advisor "Biggs, Reinette"

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    Exploring the social-ecological drivers and impacts of invasive alien plant induced regime shifts in the grasslands of the Eastern Cape, South Africa
    (Stellenbosch : Stellenbosch University, 2023-03) Mandlana, Qhamani; Selomane, Odirilwe; Biggs, Reinette; Luvuno, Linda; Malgas, Rhoda; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Invasive alien plant species (IAPs) are currently invading South Africa’s grasslands. In this study, I explore the drivers and social-ecological impacts of invasive alien plant induced-regime shifts on the grasslands of the Eastern Cape Province in South Africa. This thesis consists of two data chapters. The first chapter (Chapter 2) synthesizes literature of the social-ecological drivers and processes underlying the invasive alien plant-induced regime shift based on the Regime Shift Database framework (RSDB). In the second data chapter (Chapter 3), I used semi-structured interviews to understand how the regime shift is perceived to affect the ecosystem services provided by grasslands and the well-being of the people who live around the Upper Tsitsana Catchment, Eastern Cape. Chapter 2 identified drivers that promote the invasion of IAPs that potentially push grassland across a critical threshold to cause a shift from a grass-dominated regime (grassland) into a woody invasive alien plant-dominated regime. These drivers included (1) the introduction of certain alien plants for various agricultural and aesthetic purposes that are now problematic; which reproduce, naturalize, become invasive, and disrupt grassland structures and functions, (2) land and soil disturbance caused by non-sustainable land uses and inappropriate land management practices, timber extraction and overgrazing, which facilitate the expansion of IAPs, (3) increased carbon dioxide (CO2) levels that promote invasive plant growth due to their leaf-level traits associated with carbon capture, (4) land abandonment that creates less competitive conditions for native grasses, and thus more opportunities for IAPs to invade and dominate, (5) high rainfall, which increases water content in the surface layer, and allows IAPs to absorb water better than native vegetation due to their high infiltration rates and superficial root system which favours their invasion success, and (6) clearing of invasive alien plants which can promote their growth due to re-sprouting seedlings. In this chapter, I have also highlighted the key feedback mechanisms that maintain the grassland regime (i.e., fire) and invasive alien plant-dominated regime (i.e., high rate of germination and seed production) using a causal loop diagram (CLD). Understanding the interaction between the key drivers and feedback dynamics can inform integrated planning processes to monitor, reduce, and prevent the ability of IAPs to cause regime shifts. Chapter 3 reports interview results amongst the respondents (n=50) of the Upper Tsitsana Catchment that are dependent on the grasslands for their everyday life for farming, grazing and cultivation in the Eastern Cape Province. More than 90% of the respondents stated that invasive alien plants, especially Acacia dealbata (silver wattle) and Acacia mearnsii (black wattle) have caused substantive changes and now dominate the grasslands of Upper Tsitsana Catchment. On the one hand, respondents stated that the invasion by these woody IAPs have many negative impacts such as reduced water supply, poor grazing areas, crop yields and providing refuge for criminals, and would like to see a decrease in Acacia mearnsii and Acacia dealbata dense stands. The respondents mentioned benefits provided A. mearnsii and A. dealbata such as fuelwood, building material, medicine, and livestock feed. The benefits of IAPs create conflicts and debates on whether these species should be controlled to provide the mentioned benefits. Policymakers and researchers should engage with land-users to understand their perceptions towards IAPs to address these conflicts. This chapter also highlighted that the fight against IAPs is currently spearheaded by the Working for Water (WfW) program through a tree debarking and chemicals approach. Despite the current control measures, these plants are re-establishing, forming dense stands, and invading larger areas, which makes it increasingly difficult to restore the native grassland. Rapid strategic management options are required in addition to the control methods by WfW to prevent further shifts that will drive the grassland ecosystem and human livelihoods into even more vulnerable conditions.