Annual monitoring reveals rapid upward movement of exotic plants in a montane ecosystem

Kalwij, Jesse M., Robertson, Mark P. and van Rensburg, Berndt J. (2015) Annual monitoring reveals rapid upward movement of exotic plants in a montane ecosystem. Biological Invasions, 17 12: 3517-3529. doi:10.1007/s10530-015-0975-3

Author Kalwij, Jesse M.
Robertson, Mark P.
van Rensburg, Berndt J.
Title Annual monitoring reveals rapid upward movement of exotic plants in a montane ecosystem
Journal name Biological Invasions   Check publisher's open access policy
ISSN 1387-3547
Publication date 2015-09-16
Year available 2015
Sub-type Article (original research)
DOI 10.1007/s10530-015-0975-3
Open Access Status Not Open Access
Volume 17
Issue 12
Start page 3517
End page 3529
Total pages 13
Place of publication Dordrecht, Netherlands
Publisher Springer
Language eng
Abstract There is increasing evidence that invasive species are threating montane ecosystems globally. However, trends in species distribution are difficult to observe directly due to a lack of data with suitable spatio-temporal resolution. Here, we aimed to detect spatio-temporal trends in exotic plants in a montane ecosystem, and to determine which drivers had a role affecting these trends. Each year, for a period of 7 years, we recorded the upper elevational range limit of exotic plant species in road verges along an elevational gradient of 1500–2874 m a.s.l. in southern Africa. We fitted repeated-measures ANOVA models to test if upper elevational range limits changed over time. Generalized least squares models showed that exotic richness of annuals increased by 3.9 species per year. Also, the upper elevational range limits of established exotics ascended by 24.5 m/year for annuals (N = 17 species), and by 9.7 m/year for perennials (N = 26). These upward trends were too rapid to be explained by slow-acting drivers such as climatic change or time since species introduction. The rates of increase indicate that many exotics were not yet in equilibrium with the environment and, therefore, had not been in the region long enough to have filled their potential niches. Exotic species could reach much higher elevations than expected, indicating that current prediction models are likely an underestimation of potential distributional ranges. The spatial clustering of upper elevational range limits around potential points of introduction indicates ongoing human-mediated propagule pressure as the major cause of rapid exotic range expansion, especially along roads and near dwellings. Montane road verges are regularly disturbed by erosion and maintenance, creating unoccupied habitats, while traffic in the form of vehicles and tourists facilitates the introduction of new species. This suggests that easily accessible montane ecosystems are much more susceptible to invasions than previously assumed, due to a combination of anthropogenic disturbance and ongoing propagule pressure.
Keyword Alpine
Alien plants
Established range
Potential range
Range edge
Sani Pass
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2016 Collection
School of Biological Sciences Publications
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