Is it worth the effort? Spread and management success of invasive alien plant species in a Central European National Park

The management of invasive alien species (IAS) in protected areas has become increasingly important in recent years. In this study, we analyse IAS management in the bilateral National Park Thayatal-Podyji at the Austrian-Czech border. Based on two surveys from the years 2001 and 2010 and on annual management data from 2001-2010 we analyse changes in distribution and the efficiency of IAS management of three invasive alien plants (Fallopia x bohemica, Impatiens glandulifera, Robinia pseudoacacia). In 2010, the three study species had invaded 161 ha (2%) of the study area. Despite a decade of management, F. x bohemica has become widespread, whereas I. glandulifera distribution has decreased strongly. The most widespread species, R. pseudoacacia, has declined substantially in cover, but the area invaded has increased. From 2001 to 2010, annual management effort declined by about half. Management effort per hectare and decade was highest for F. x bohemica (2,657 hours), followed by R. pseudoacacia (1,473 hours) and I. glandulifera (270 hours). Management effort for achieving the same amount of reduction in population size and cover was highest for R. pseudoacacia, followed by F. x bohemica and I. glandulifera. We conclude that substantial effort and resources are necessary to successfully manage the study species and have to be provided over prolonged time periods, and thus continued management of these species is recommended. We highly recommend a systematic approach for monitoring the efficiency of IAS management projects in protected areas.