Drivers of compositional turnover of narrow-ranged versus widespread naturalised woody plants in South Africa

Abstract

IntroductionAlien trees and shrubs have become increasingly common invaders globally and have caused major negative impacts to ecosystems and society. Non-native woody plant species make up the majority of legislated invasive alien taxa in South Africa and contribute substantially to recorded negative impacts. It is of management interest to elucidate the macroecological processes that mediate the assembly of alien taxa, as this is expected to be associated with anthropogenic factors (e.g., human activity, introduction events, pathways of propagule dispersal mediated by humans) and bioclimatic factors (such as diurnal temperature range and precipitation gradients). These analyses require large species-occurrence datasets with comprehensive sampling across broad environmental conditions. Efforts of citizen scientists produce large numbers of occurrence records in a consistent manner which may be utilised for scientific investigations.MethodsResearch Grade occurrence data on naturalised plants of South Africa were extracted from the citizen scientist platform iNaturalist. Sampling bias was mitigated using statistical modelling of background points estimated from a Target Group of species which identifies well sampled communities. The drivers of assembly for alien plants at different range sizes were identified using multi-site generalised dissimilarity modelling (MS-GDM) of zeta diversity. The predicted compositional similarity between all cells was computed based on the subset of identified well sampled communities and using generalised dissimilarity modelling (GDM). From this, alien bioregions were identified using a k-means cluster analysis.Results and DiscussionBioclimatic factors significantly influenced community turnover in inland areas with large diurnal temperature ranges, and in areas with high precipitation. Communities separated by large geographical distances had significantly different compositions, indicating little contribution of long-range propagule movement by humans, and the presence of localised introduction hubs within the country which harbour unique species compositions. Analyses also showed a significant contribution of road density to turnover, which may be moderated by the habitat service provided by road verges. The same is true for natural dispersal via rivers in arid areas. The distribution of naturalised tree and shrub species is geographically clustered and forms six alien bioregions that are distinct from the South African biomes defined by native species distributionanalysis.

Drivers of compositional turnover in narrow‐ranged and widespread dragonflies and damselflies in Africa

“…However, they are inadequate in many sites when exploring between‐site species turnover. Although stringent criteria for site selection are available (e.g., de Beer et al, 2023), they do not apply well here as biodiversity data are typically scarce in Africa.…”

Optimizing the Benefits of Invasive Alien Plants Biomass in South Africa

“…Invasive alien plants have been gaining dominance in the natural and managed ecosystems worldwide as shown in the Millennium Ecosystem Assessment [6,[24][25][26]. Several ecosystems in South Africa have been disturbed to varying extents, inclusive of the impact of invasive alien plants [27][28][29][30][31]. Invasive alien plants are now a global issue and have the potential to alter ecosystems and inflict loss of biodiversity [24,25,[32][33][34].…”

“…Invasive alien plants are now a global issue and have the potential to alter ecosystems and inflict loss of biodiversity [24,25,[32][33][34]. They are now dominating many ecosystems (both terrestrial and aquatic) in South Africa, effecting reduced water flow in rivers where they are common, and have been recognized as a national problem [6,30,31]. The "Working for Water Programme (WfW)", a systematic control and management program of invasive alien plants in South Africa, was conceived in 1995, shortly after South Africa gained democracy, with the goal of conserving ecosystem services (e.g., water) and biodiversity, and addressing the country's socio-economic concerns [6,30].…”