Kelemen et al. (2016) Applied Vegetation Science

Kelemen, A., Valkó, O., Kröel-Dulay, Gy., Deák, B., Török, P., Tóth, K., Miglécz, T., Tóthmérész, B. (2016): The invasion of common milkweed (Asclepias syriaca L.) in sandy old-fields – Is it a threat to the native flora? Applied Vegetation Science, doi: 10.1111/avsc.12225


Abstract
Questions
Common milkweed (Asclepias syriaca L.) is an invasive ‘super species’ that has invaded extensive areas in Europe, forming novel ecosystems. One study has reported neutral effects of common milkweed on the native flora of sand dune grasslands in Hungary after the removal of invasive pine plantation. However, the effects of common milkweed on native flora more generally are unknown. Focusing on the potential effect of milkweed, we tested the following hypotheses: (1) the cover of native grassland species decreases with increasing cover of common milkweed; and (2) native species with low specific leaf area (SLA), height, seed mass and clonal spreading ability (i.e. low competitive ability) are more likely suppressed by milkweed compared with natives with high competitive ability.

Location
Late successional sandy old-fields invaded by milkweed in the Great Hungarian Plain (Kiskunság, central Hungary).

Methods
We recorded the cover of vascular plants in seven old-fields; in each old-field we sampled 12 plots including plots with different milkweed cover and control plots without milkweed. We used linear mixed effect models for exploring the effects of milkweed on the species richness and cover of native grassland species. To identify the common traits of the most affected native species, we used trait-based analyses; we studied leaf–height–seed traits and clonal spreading ability.

Results
We detected no effect of common milkweed on total species richness, but it had a negative effect on the cover of grassland species. The negative effect of common milkweed was most pronounced on the cover of species with low SLA, low seed mass and low clonal spreading ability.

Conclusions
Our results suggest that native, late successional sandy grasslands invaded by common milkweed form undesirable novel ecosystems because of significant negative impacts on the cover of native grassland species, especially those species with low competitive ability. For these species, management of milkweed might be needed to ensure their persistence in sandy grasslands in this landscape.

Keywords
Clonal spreading, Competition, Functional traits, Novel ecosystem, Old-field, Plant invasion, Sandy vegetation, Seed mass, Specific leaf area

Fenesi & Botta-Dukát (2012) Journal of Plant Ecology

Fenesi, A.; Botta-Dukát, Z. (2012): Phenotypic divergences induced by different residence time in invasive common ragweeds. Journal of Plant Ecology 5:174-181.

Abstract
Aims: Possible shifts in the phenotypic performance along invasive plants’ spreading route are rarely examined due to the discontinuous and incomplete records of exotic species. As the invasion history of common ragweed (Ambrosia artemisiifolia L.) is well documented in Hungary, its residence time is known for each location. By sampling a sequence of older to more recently established populations, we aimed to determine (i) whether there are phenotypic divergences along the historical spreading route of A.artemisiifolia; (ii) which traits are under selection during the invasion process and (iii) the extent of maternal effects on the individual's performance.
Methods: We used a hierarchical sampling design to collect seeds from 64 individuals belonging to eight sites in four residence time categories (seven populations along the historical spreading route of ragweed in Hungary and one recently invaded site in Romania). We selected four large and four small individual plants in each population to control for maternal effects. The offspring were reared in a common garden located in Romania. Five vegetative phenotypic traits were measured at the end of the experiments and used in the subsequent analysis (plant height, basal diameter, number of secondary axes, length of the longest secondary axis and biomass). To summarize the variation of these highly correlated traits, principal component analysis was performed first and then the important components were used in linear mixed effect models.
Important Findings: The residence time categories were significantly distinguished by the first component, which compresses the variation of all five measured traits. The measures gradually decrease from populations with the longest residence time (introduced more than 65 years ago) towards the most recently established populations (established less than 30 years ago). These differences might reflect the invasion history of the populations: the longer the residence time the higher the chance to develop relevant traits beneficial in invasion process. The size of the mother plant significantly influenced not only the seed mass (inversely) but also the adult performance of its offspring (directly).

Keywords 

Ambrosia artemisiifolia, maternal effect, phenotypic divergence, plant invasion, residence time