Tree species diversity of agro- and urban ecosystems within the Welgegund Atmospheric Measurement Station fetch region

Abstract

Rapid worldwide urbanisation has noteworthy ecological outcomes that shape the patterns of global biodiversity. Habitat loss, fragmentation, biological invasions, climate- and land-use change, alter ecosystem functioning and contribute to the loss of biodiversity. This warrants the study of urban ecosystems and their surrounding environments since biodiversity is essential for economic success, ecosystem function and stability as well as human survival, due to the fact that it provides numerous ecosystem goods and services. Furthermore, agroecosystems are continuously expanding to meet human needs and play a distinctive role in supplying and demanding ecosystem services, consequently impacting biodiversity. With anthropogenic impacts on ecosystems increasing exponentially, pressure on ecosystem services are intensifying and ultimately unique urban environments that are perfect for the establishment of alien species is created. The proportion of native species in urban areas has increasingly been reduced due to urbanisation, while the proportion of alien species has markedly increased. Trees are normally not considered as typical weedy plants, but many species are invasive aliens in different parts of the world. Trees are generally long-lived and easy to locate, which make trees good indicators of long-term climate conditions, physiognomy and overall vegetation structure. Knowledge of urban floras is vital to improve and maintain the services provided by these areas, as well as aiding in conservation and management practices in urban and surrounding ecosystems. The aim of this study was to compile a detailed floristic account of the woody vegetation of agro- and urban ecosystems in a 60 km radius around the Welgegund Atmospheric Measurement Station. Bushclumps in different land-cover types were targeted, namely gardens, grasslands, hillsides, plantations, ridges, riparian areas, roadsides, sandy areas, streets and urban open spaces and included tree measurement along a belt transect. Results indicated clear differences between land-cover types as well as alien and indigenous species diversity and composition, which were indicated by means of ordinations. A total of 169 woody species were recorded, with aliens comprising 114 of these species. Tree species diversity was higher in urban areas, but mainly constituted of alien species, whereas species richness was higher in natural areas. Meaningful correlations occur between the socio-economic status of cultivated areas and the categories of alien invader trees. DCA, NMDS, Linnear Mixed Models displaying effect sizes, diversity indices and basic statistical analyses were performed using the data. Variation in tree species composition and diversity occur between the different land-cover types