Repeated monitoring as an effective early detection means : first records of naturalised Solidago gigantea Aiton (Asteraceae) in southern Africa

Abstract

Early detection ofemerging invasive plants depends onmaximizing the probability of detecting newpopulations. Repeated surveys along a gradient of environmental conditions or in areas exposed to high propagule pressure provide a potentially efficient strategy for early detection of alien species. The long-term monitoring of such an area resulted in the documentation of the first naturalised Solidago gigantea Aiton (Asteraceae) population for southern Africa. This population consisted of c. 45 individuals growing in two locations on unmanaged grassland in the Drakensberg Mountains at an elevation of 1619 m a.s.l. Solidago gigantea readily invades unmanaged European grasslands, altering biomass and transforming habitats. Moreover, since goldenrods (Solidago spp) are perennial species reproducing through a large number of wind-dispersed seeds and belowground rootstocks, these species appear well pre-adapted to the fire-prone grassland biome of South Africa. We therefore suggest early-stage eradication of S. gigantea before it potentially becomes an unmanageable and costly invasive species in this region. This study supports long-termmonitoring programmes as an effective means for early detection of new invasive species.