Mowing: Cause, but also a solution for invasive plant Erigeron annuus in a landfill

Background/Question/Methods

In slopes of a sanitary landfill in Korea, invasive plant Erigeron annuus (which is one of the most monitored invasive species in Korea) is a dominating plant. As landfill is dominated by this invasive species, revegetation of landfill slopes by native species is seriously delayed. Therefore, for the management of this species, studies to find the reason of dominance of this species and proper solutions were researched. Comparison against native species (survival ability, allelopathy, seed production etc.) and possible solutions (native species seed spray and transplanting, removing above ground biomass or roots) were carried out. As mowing was frequently performed in the landfill, quadrats (1mⅹ1m) were established where Erigeron annuus dominating areas and protected from mowing. And two areas where Erigeron annuus species are increasing were also monitored, without protection from mowing. Quadrats were monitored for 4 years (2006-2009). In 2009, 4 treatments (Control - no mowing, mowing once, mowing twice, mowing three times) were established for mowing at summer when flower stems of Erigeron annuus are taller than other native species, to find out if mowing proper times and in proper seasons can manage invasion of the species. 

Results/Conclusions

Erigeron annuus species did not show any better performance in comparative studies. However, in quadrat research, protected (unmowed) quadrats showed 70% coverage decrease of Erigeron annuus while mowed quadrats showed over 30% increase of coverage. As Erigeron annuus spreads seeds in late summer (much faster than most native species) and most of the mowing activities are performed in early fall (when plants are tallest), mowing activity of the landfill certainly brings benefits to this invasive plant compared to other native species (also rosettes of Erigeron annuus does not damaged by mowing). As the Erigeron annuus species gets advantage in mowing of early fall, changing mowing season to flowering seasons of Erigeron annuus species would be a simple and reversal solution. Erigeron annuus with one time mowing surprisingly showed increase of biomass (and ratio) of the flowers, as the plant grows small flower stems after main flower stem has been cut. However, after cutting tree times, the weight and ratio of flowers were significantly decreased. Therefore, by changing mowing season into summer when Erigeron annuus are blooming, and by mowing over three times would prevent increase of Erigeron annuus species and will also be able to control the species invasion.