Environmental and land-use variables determining the abundance of Ambrosia artemisiifolia in arable fields in Hungary.

Ambrosia artemisiifolia is the most noxious invasive species of weed in Hungary. The aim of this study was to quantify the environmental and land-use factors that explain the variance in its abundance in arable fields. A survey of 243 arable fields was carried out across Hungary, and 19 environmental and 12 land-use factors were measured. These were used as explanatory variables in classification and regression tree models. The abundance of A. artemisiifolia was significantly higher at the edges than at the centres of fields. The most important land-use variables explaining the variance in abundance of A. artemisiifolia were crop type and crop cover, with the highest abundance recorded in sunflower fields and fields with low crop cover. The following explanatory environmental variables were associated with significantly higher A. artemisiifolia abundance: sandy or acidic soils, mean April precipitation > 39 mm, mean annual precipitation > 592 mm and mean May temperature < 15.5 °C. Ambrosia artemisiifolia was significantly less abundant in fields with soils containing high concentrations of Na, K and Mn. Both farmers and nature conservationists should be made aware of the conditions and practices that favour ragweed so that they can develop effective and selective ragweed control practices, particularly in arable habitats with a high diversity of weeds.