As a consequence of human land-use change and globalization the successfully spreading non-indigenous species occupy large areas and make a more and more problem. In Hungary, one of the most important non-indigenous species is the ragweed (Ambrosia elatior L.) which makes not only agrarian and nature conservational problem, but also human medical problem, because its pollen is seriously allergenic.
The ragweed is regarded principally (mostly?) as weed of cultivated and abandoned agricultural lands, but it occurs also in other semi-natural habitats and in order to make a complex defence strategy we should know more about its distribution pattern on landscape scale.
The aim of our study was to find out the role of different (man-made, semi-natural and natural) habitats in a mosaic landscape in the establishing and sustaining of ragweed- populations.
We assigned 16, respectively 5 km2 large sampling site in the region of Danube-Tisza Interfluve, which represent the regional diversity of land-use types and intensity. In every important habitats of the region – in agrarian, abandoned agrarian, forest plantation and semi-natural habitats - we made in 3 replicates per sampling site 400 m2 large relevés. Thus we detected the plant species richness, included the ragweed abundance in about 600 locations of 16 habitat types. On the basis of relevés we examine (analyse?) the dependence of ragweed presence and abundance on the land-use types and present vegetation. With the use of archive ariel photos from 1950, 1990 and 2000 we analyzed the connection between the occurrence of ragweed and the land-use change of the last 50 years.
According to our results the ragweed is the most common on abandoned agricultural fields from the studied and occurring habitats, within them it reach the larges abundance on young old-fields. At the same time on the old-fields, where closed secondary grassland could establish, the abundance of ragweed is lower than for example on plough-lands or alien (choice, selected) poplar plantations. In the remained semi-natural habitats (grasslands and forests too) the ragweed occurred only rarely and with low abundance, which refer to that these habitats could impede the distribution of the ragweed (or other non-indigenous species).
The present and past land-use pattern determine the occurrence and abundance of ragweed at our study region, thus the exact knowledge of it could help to develop a more successful defence strategy again this species. We suggest that especially the more differentiated judgement of old-fields as present is necessary in Hungary