Short-term effects of the control of the invasive plant Asclepias syriaca: Secondary invasion of other neophytes instead of recovery of the native species

Abstract

Question: This study aimed to assess the impact of the invasion of Asclepias syriaca, a perennial non-native herbaceous species, on basic soil attributes and vegetation composition, and to study the effect of mechanical control, namely the cutting of Asclepias, on target and other plant species. Location: Sandy region of Kiskunság National Park, Hungary, Central Europe. Methods: In ten old-fields, four 4 m × 4 m plots were established (n = 40), of which three were invaded by Asclepias, and one was uninvaded. The invaded plots were treated as: (1) all Asclepias shoots removed, (2) half of the Asclepias shoots removed, or (3) untreated. The treatment was conducted twice a year in summer during the period 2019–2021. Before the first treatment, soil and vegetation were sampled. Afterwards, vegetation monitoring was performed twice a year: the cover of each vascular plant species and the number of Asclepias shoots were recorded in each plot. Result: There were no differences in the studied soil attributes between the uninvaded and invaded plots. However, there were differences in vegetation composition, namely, the cover of sand grassland specialists was higher in uninvaded plots. Short-term cutting negatively affected Asclepias after two years. The cover of specialists did not change in response to treatments, but the cover of other neophyte plant species increased. Conclusions: Based on our results, the invasion of Asclepias changes the vegetation composition, but not the soil. Although short-term mowing can reduce the cover of Asclepias, but the grassland specialist plants do not regenerate; instead, secondary invasion occurs. We conclude that more time or additional treatment is required for native plant recovery.