How flower visitation of remnant grassland patches is affected by commercial timber plantations and an invasive alien species (Rubus cuneifolius)

[摘要] ENGLISH ABSTRACT: Our planet is in the midst of a biodiversity crisis, with factors such as land transformation,climate change, anthropomorphic disturbance and invasive species acting together to threatenbiodiversity. In South Africa, with minimal natural wood resources, commercial forestry is oneof the most abundant forms of landscape transformation. However, a third of the land insidemany plantations has been set aside for conservation as unplanted remnant grassland patches(RGPs). These areas are subjected to an additional negative impact by invasive alien species,namely Rubus cuneifolius (American bramble), a weed that is particularly problematic in andaround forestry plantations in South Africa. The grassland biome of South Africa is extremelydiverse and is of vital importance for the ecosystem services it supplies. Despite this, thegrassland biome is under threat as this is where much of South Africa's forestry plantations arelocated. Driven by anthropomorphic disturbance, pollinators are in decline. Landscapetransformation of natural areas for forestry plantations is likely to affect plant-pollinatorinteractions which will affect ecosystems and biodiversity. However, it is not known to whatextent these ecosystems are affected. It is thought that the impact depends on the complexityof the ecosystem in question, and analyses at the network-level provide insights into therobustness of ecosystems in the face of biodiversity loss. Thus, this study evaluates the effectof natural habitat fragmentation and invasion of the alien species, R. cuneifolius, on flowervisitation networks of South African grasslands.The study was conducted in the KwaZulu-Natal Midlands within a commercial timberplantation and a neighbouring protected area (PA). Flower-visitor observations were carriedout in uninvaded protected areas and RGPs and in protected areas and RGPs invaded by R.cuneifolius. I found that RGPs within commercial forestry plantations successfully decreasethe negative effects of land transformation on the grasslands of the KwaZulu-Natal Midlands,and flower visitation network patterns are largely maintained in these habitat fragments.However, within RGPs, invasion by R. cuneifolius affected the composition and the interactionnetwork structure of flower-visitor and plant communities.The fact that there are unplanted areas within commercial forestry plantations is positive forbiodiversity conservation in South Africa. Research has indicated that these areas successfullyaid in the conservation of biodiversity and ecosystem functioning. Due to the positive influencethat RGPs have on conservation in fragmented and transformed landscapes, it is critical thatthese unplanted areas are retained. However, the effects of bramble invasion are more intensewithin RGPs than within protected areas, and therefore, it must be a priority to keep these areasundisturbed. R. cuneifolius has been found to have devastating effects on ecosystem functionand network structure. It is also a category 1 invasive plant within South Africa, and its removalis required by law. Therefore, the removal of bramble must be a management priority.

[发布机构] Stellenbosch University