Drivers of Ambrosia artemisiifolia abundance in arable fields along the Austrian-Hungarian border

The Carpathian Basin is one of the most important regions in terms of the invasion of the common ragweed (Ambrosia artemisiifolia) in Europe. The invasion history of this weed, however, seems to have been assessed differently in Austria and Hungary: scientists in both countries assumed that this species had become abundant earlier and had caused more problems in their own than in other country. The goal of this study is to resolve the historical misunderstandings and scrutinize the related popular beliefs by a concise literature overview and an extensive analysis of the current patterns in ragweed infestations in crops in the borderlands in eastern Austria and western Hungary. The abundance of A. artemisiifolia was measured in 200 arable fields across the region, along with 31 background variables. Data were analysed using binomial generalized linear models (GLM), decision tree models and variation partitioning. Ambrosia artemisiifolia occurred more frequently in Hungary, but there were no significant differences in the proportion of larger cover values recorded in these two countries, and ‘cover values > 10%’ were even slightly more common in Austria. We found that previous crops of maize and soya bean and conventional farming were associated with the higher abundances in Austria, while organic farming was associated with relatively higher frequencies of heavy infestations in Hungarian fields. In the overall analysis crop cover was the most important variable with low crop cover associated with high ragweed abundance. Temperature and phosphorous fertilizer were negatively, while precipitation and soil phosphorous concentration positively associated with the abundance values. Land-use variables accounted for more of the variance in the abundance patterns of common ragweed than environmental variables. The current patterns in ragweed distribution might indicate that a saturation process is still underway on the Austrian side. The saturation lag of 20–30 years is possibly due to several factors and the role of the Iron Curtain in determining cross-border exchange of propagules could be decisive. Nevertheless, the discrepancies uncovered in the accounts of the invasion of Hungarian and Austrian authors might also be seen as legacies of the Iron Curtain, which were caused by mutual limitations on access to national data and literature of the other country in a critical period of rapid ragweed spread. These discrepancies, that had a long-lasting effect on the work of scientific communities, are documented here in detail for the first time.