The impact of high rainfall and flood events on Eucalyptus camaldulensis distribution along the central Breede River

[摘要] ENGLISH ABSTRACT: Eucalyptus camaldulensis Dehnh., or River Red Gum, is a commercially valuable yet recognisedinvasive alien plant (IAP) of riparian zones throughout South Africa. The invasive potential of E.camaldulensis is widely recognised, with specific regulations aimed at the management of E.camaldulensis. E. camaldulensis is known to use large amounts of water, reduce biodiversity,change river morphology and impact hydrological regimes of rivers. In the native range throughoutAustralia, E. camaldulensis displays a distinct relationship between rainfall, and flood events, forseed dispersal, germination and establishment, and consequently spatial extent, yet little is knownabout the relationships in the South African context. The aim of this project was to assess theimpact of high rainfall and flood events on the establishment and distribution of E. camaldulensisalong the Middle Breede River, between Worcester and Swellendam in the Western Cape, byestablishing the current spatial extent of E. camaldulensis along the river, identifying flood eventssince 1950 and evaluating the impact rainfall and flood events had on the spatial extent thereof.Aerial imagery, rainfall, discharge and river level data was obtained dating back to 1980, as well asfield data comprising of GPS-bounding of E. camaldulensis stands. Additionally, densitymeasurements were obtained and interviews conducted with land users. Spatial analysis of aerialimagery, coupled with perimeter (GPS) data and density data were used to conduct spatio-temporalanalysis, employing GIS and conventional statistical approaches to address the various objectives.Results indicated E. camaldulensis stands had a small overall increase in spatial extent since 1980.Flooding and rainfall events coincided with an increase in occurrence of E. camaldulensis withelevated river levels and frequent flooding, while spatial variation of this relationship was observed.The hydrological regime of the Breede River coincides with a slow increase in spatial extent of E.camaldulensis stands, but no affirmation of a positive real-world relationship was possible using theavailable data. Results further suggested, based on the current age class composition, that existingstands originated roughly during 1980, possibly due to commercial forestry related seeding into theriver. Reduced fragmentation between stakeholders, educational programmes and improvedreporting systems were recommended for improved IAP management within the area.

[发布机构] Stellenbosch University