Anikó Csecserits, Melinda Halassy, Tamás Rédei, Katalin Szitár and Zoltán Botta-Dukát
MTA Centre for Ecological Research, Institute of Ecology and Botany, Vácrátót, 2163, Alkotmány Srt. 2-4, Hungary
The invasion of alien plant species can cause long-lasting impacts on plant communities, changing the diversity and functioning of native plant communities. This is especially true for intensively developing habitats, such as abandoned agricultural fields, in which alien species can have a detrimental effect as it impedes the regeneration of native plant communities. There are many hypotheses explaining the impact and success of alien species, most of which highlight the importance of functional characteristics of the non-native species. According to the trait divergence hypothesis, novel traits of alien species may promote these species to use their resources differently than the resident community, thus providing a competitive advantage for the alien species.
Milkweed is a widespread alien species in Hungarian Lowlands, especially in abandoned agricultural fields, causing nature conservation problems. Thus, it is important to understand the reason behind its success to enhance the effectiveness of management measures.
As a first step, we evaluated the position of milkweed in the local community. Our questions were: (i) does the non-native species, Asclepias syriaca, have different trait compositions than the native local species? (ii) is there a decline in native plant richness and abundance because of the non-native species during succession? (iii) do native species, which are most influenced by the spread of milkweed, have a similar or different trait composition compared to Asclepias syriaca?
We conducted our study in the Hungarian lowland, in the sandy area between the Danube and Tisza rivers. The vegetation of old-fields comprising four different age-groups (i.e. 35-26, 25-13. 12-7, 6-2) were studied from 2000 to 2017. We compared the trait spectrum of milkweed with the species from the local species pool on the basis of twelve traits. The effect of milkweed on native plant richness and abundance were evaluated using mixed effect models. The trait spectrum of milkweed was different from most of the local species, therefore, this species represents a novel trait combination for this region. During succession, the abundance of Asclepias syriaca increased in every age-group, while the abundance of native perennial species only increased in recently abandoned fields. We found a correlation between the changes of Asclepias syriaca abundance from 2000 to 2010 and the changes of perennial herb species from 2000 to 2010. Milkweed had a larger effect on the perennial herb species, showing similar trait composition. The better resource-use of Asclepias syriaca may be a possible reason for it, but this requires further study.