Garden waste deposits as a source for non‐native plants in mixed deciduous forests

Abstract

AbstractQuestionIs illegal garden waste dumping in mixed deciduous forests a source for establishment of non‐native plants in deciduous forests?LocationNorthwestern Switzerland.MethodsWe quantified the amount of illegally dumped garden waste at 20 sites over 1 yr and compared the soil conditions, species richness and abundance of plants in the ground vegetation at disposal sites with those at 20 control sites in urban deciduous forests.ResultsWe found that illegal garden waste dumping frequently occurs in urban forests. At single sites, 0.1–12.5 m3 (mean: 2.6 m3) garden waste was dumped per month, resulting in a total annual amount of 2.2–35.8 m3 (mean: 17.8 m3) waste deposited. Thirty‐seven of the 163 plant species recorded were not native to Switzerland. All 37 non‐native species were recorded in waste disposal sites, but only three of them in control sites. Thus, garden waste dumping sites harboured a larger number of non‐native species than control sites, but the two groups of sites did not differ in number of native species. The species composition also differed between disposal and control sites: larger proportions of species typical of disturbed habitats, more therophytes and species with autochorous seed dispersal were recorded in disposal sites than in control sites.ConclusionsWe provide evidence that numerous non‐native horticultural plant species escape from dumping sites and colonize forests. There is an urgent need to increase awareness of garden owners concerning problems associated with illegal garden waste dumping.