The impact of Gunnera tinctoria(Molina)Mirbel invasions on soil seed bank communities

Aims In recent years,there has been an increasing interest in the impact of invasive alien plant species on the soil seed bank.Soil seed banks play an important role in determining the composition and dynamics of the vegetation through time.Therefore,an ability to form a persistent seed bank and/or a capacity to alter the structure of the seed bank of invaded communities could be important factors in determining the success of many alien plant species.In this study,we report on a detailed assessment of the characteristics of the seed bank community associated with the herbaceous plant invader,Gunnera tinctoria,a newly emerging and potentially globally significant invasive plant species.This species,native to South America,is invasive in a range of wet habitats in Europe,Australasia and the USA.Methods A comprehensive assessment of the seed bank of invaded and comparable uninvaded areas was made at two points in time(May and October),at three sites in western Ireland.The seedling emergence approach was used to assess the structure(diversity,dominance and abundance)of the soil seed bank.Differences between invaded and uninvaded seed bank communities were investigated at the spatial scales of site,plot and depth.Important Findings Gunnera tinctoria formed a large persistent seed bank at the study sites.Approximately 30000 seedlings per square metre emerged from soils collected from invaded areas,of which 30%were found in deep soil layers.Seedlings of this invader represented 53–86%of the total number of seedlings associated with invaded areas.Both the transient and the more persistent component of the seed bank of invaded communities were significantly less diverse and abundant than those of uninvaded areas,and were characterized by higher dominance,even when seedlings of the invader were not included in the analysis.The seed bank of invaded areas was largely composed of seeds of agricultural weeds in addition to those of the invader.These results suggest that G.tinctoria has the capacity to profoundly alter the seed bank of invaded communities.These results have direct relevance for the development of control and management strategies,for this and other comparable invasive species,which should account for both quantitative and qualitative alterations in the seed bank community.Our study also suggests that control measures that result in disturbance of areas colonized by G.tinctoria could promote the germination of undesirable weeds.