Authors: Sonkoly, Judit; Takács, Attila ;Molnár V., Attila;Török, Péter;

Humanity intentionally spreads several species, accompanied by other plant species dispersed accidentally. Although the global trade of horticultural plants and substrates may disperse large quantities of propagules, it has hardly been studied from an ecological point of view. We studied the viable seed content of potting substrates to assess (i) the seed content and composition of substrates, (ii) the effect of substrate composition on seed content, and (iii) whether there are common characteristics of the dispersed species. We found 438 seedlings of 66 taxa and found that 1 litre of substrate contains an average of 13.27 seeds of 6.24 species. Seed content of the substrates was highly variable and substrates containing manure contained a substantially higher number of species and seeds than substrates without manure, indicating that this pathway is an interplay between endozoochory and accidental human-vectored dispersal. Our results demonstrate that potting substrates can disperse large quantities of seeds of a wide range of species over large distances. We conclude that this kind long-distance dispersal may have complex effects on plant populations and communities; however, as this dispersal pathway is largely understudied and has hardly been considered as a type of LDD, its ecological and conservational consequences are unknown.