Montane ecosystems provide an excellent opportunity to observe population dynamics on the upper elevational limit of species distribution ranges. The Sani Pass road covers an elevational range of 1500–2873 m a.s.I. located in the Mkhomazi Wilderness area of the Drakensberg, South Africa — a biodiversity hotspot with a spectacular scenic appeal. Moreover, the area is relatively undisturbed by anthropogenic factors and easily accessible with a 4×4 vehicle. Therefore, this road provides an excellent opportunity to monitor trends in exotic species distribution ranges.

In this longitudinal project, we annually record the upper elevational limits of all exotic plant species in the road sides verges of a 20-km long ungravelled section of this road. The lower section of this section is gradually being tarred. Since the start of this project in 2007, we have observed more than 110 exotic plant species (Kalwij et al. 2008), and we regularly discover exotic species that are were previously unknown to the area (Kalwij et al. 2014). Interestingly, this project shows that the upper elevational ranges of exotics increase at a rate that is too rapid to be explained by slow-acting drivers such as climatic change or time since species introduction (Kalwij et al. 2015). One explanation of these trends is that exotic species are usually generalist species but with traits that allow them to flourish in the harsh conditions of a montane ecosystem (Steyn et al. 2017).

Mounting data suggest that the spatio-temporal dynamics of exotic plant populations have not reached their equilibrium yet. Moreover, current road construction activities are likely to be an important driver of future changes in exotic plant population composition. Therefore, this project will continue to provide interesting data for many years to come.