Towards an understanding of plant rarity in KwaZulu-Natal


Brigitte Church, PS Goodman, E Witkowski

Ezemvelo KZN Wildlife


The conservation of rare plants is an important dimension in the preservation of biodiversity and consequently an improved understanding of the nature and determinants of plant rarity and its relationship to vulnerability to extinction could provide a basis for “proactive conservation” instead of the present day tendency for conservation actions to be “reactive”.


In this presentation we explore the relation between plant rarity and anthropogenic pressures (land transformation and use), biophysical factors, and plant traits in KwaZulu-Natal. A number of a priori hypotheses regarding plant rarity were developed from the literature. Rarity was defined as the product of plant species abundance (population size) and its distribution (extent of occurrence). Species were selected in a stratified random manner to include species from different levels of threat and rarity or commonness. As the interest of this study was KwaZulu-Natal, only KwaZulu-Natal records were used for the analysis. Although the study suffered from a paucity of data particularly on the biological traits and behaviour of each species we were able to explore rarity in terms of seed dispersal distance, stress tolerance, habitat specificity and ecological niche width. We also explored potential island effects based on a species affinity to isolated erosional land surfaces and the anthropogenic effects of utilization and land transformation.


To get an understanding of individual relations, rarity was compared with each explanatory variable independently prior to the analysis of suitable variables in a Classification and Regression tree analysis (CART Salford Systems Inc., USA) to understand the potential interactive effects of variables on rarity.


The results of this analysis indicated that niche width had the strongest influence on rarity followed by land surface while dispersal distance and habitat specificity appeared to have little or no relation with rarity of plant species in KwaZulu-Natal.


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Towards an understanding of plant rarity in KwaZulu-Natal

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