Low persistence of a monocarpic invasive plant in historical sites biases our perception of its invasion dynamics

Background/Question/Methods

The persistence of species at sites once colonized affects their distribution in the landscape. Since precise actual distribution of the species is rarely available our knowledge usually relies on cumulative records, while the issue of persistence is largely neglected. This issue is highly relevant in changing modern landscapes, especially for dynamic invasive species and unstable human-made habitats. This is even more pronounced in the case of alien species where most attention is paid to the spread and colonization. In this study, we explored the persistence of a monocarpic invasive species, Heracleum mantegazzianum in the Czech Republic.

Results/Conclusions

Of the total number of 521 historical sites, in which the species occurred between the end of the 19th century and present, it persists in 23.8% of sites. The persistence rate differed with respect to individual habitat types and the results indicate that factors that best explain the persistence are: type of habitat; urbanity; proximity to the place of the species’ introduction into the country; metapopulation connectivity; and distance to the nearest neighboring population.

The results show that using cumulative historical records as a measure of species distribution, as is often used in invasion literature, can yield seriously biased results that overestimate both the actual distribution and the rate of spread. Therefore, in the case of highly-fugitive alien species with low persistence, estimates of distribution and the rates of spread based on cumulative historical data reveal more about the distribution of habitats potentially suitable for colonization than providing an accurate picture of their real occurrence.