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North-West University (2020)

Drought effects on the herbaceous community structure of transformed Mopaneveld

Minnaar, Clarissa

Titre : Drought effects on the herbaceous community structure of transformed Mopaneveld

Auteur : Minnaar, Clarissa

Université de soutenance : North-West University

Grade : Masters of Science in Environmental Sciences 2020

Résumé partiel
Semi-arid Mopaneveld vegetation structure is driven by herbivory, fire, nutrients and rainfall variability. The floristically homogenous herbaceous layer is highly dynamic and dominated by forbs. Forb species contribute significantly to the herbaceous species diversity of Mopaneveld. The responses of Mopaneveld herbaceous layer to increasing stressors such as climate- and land-use change may be heightened by its dynamic nature. Species- and functional diversity may provide crucial information on the responses of Mopaneveld to disturbances and the effect thereof on ecosystem function and stability. Rainfall variability is a characteristic feature of savannas such as the Mopaneveld and consequently some species have developed adaptive traits to cope with unpredictable precipitation and drought. Mopaneveld was previously shown to absorb anthropogenic disturbance effects through functional trait redundancy. However, studies investigating the effect of drought on anthropogenically transformed semi-arid savannas remain limited. This study therefore, aimed to determine the response of herbaceous community composition, in terms of both species- and functional diversity, on mine dumps in the semi-arid Mopaneveld savanna to a severe drought. The severe 2015-2016 drought period provided the opportunity to investigate the response of species- and functional attributes of herbaceous vegetation to a severe drought on the transformed Mopaneveld ecosystem at Palabora Copper Mine (PC) in Phalaborwa, Limpopo. Floristic- and environmental herbaceous vegetation surveys, following a random paired sampling design combined with the 1 m2 quadrate method, were conducted at two mine dumps at PC (copper tailings dam – TD ; and waste rock dump -RD), and benchmarked against an adjacent protected area Cleveland Game Reserve (CGR), before drought and during drought release (In this study, defined as a period whereby an area received increased, but not above average, rainfall compared to a preceding drought period.). Herbaceous species were identified to species level and plant functional traits conferring drought- and stress tolerance were attributed to each species. Species- and functional trait data were used to analyse herbaceous community composition and diversity. Functional trait data were further analysed and compiled into plant functional types (PFT’s) to assess trait-based redundancy, and therefore resilience of the Mopaneveld herbaceous layer. Community-level analyses revealed that forb species diversity declined significantly in the protected area and on the TD, but not on the RD (intermediate land-use type). Forb functional trait diversity declined significantly on both mine dumps, but was more stable in the protected area.

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