Soil Seed Bank of Alien and Native <i>Cornus</i> (Cornaceae) Taxa in Lithuania: What Determines Seed Density and Vertical Distribution in Soil?

Soil seed banks of alien plant species are sources of propagules that play a crucial role in plant population dynamics. Studies on seed banks of woody alien species are crucial for understanding mechanisms of their encroachment on natural habitats. This study aimed to compare vertical distribution, density and composition of seed banks formed by native <i>Cornus sanguinea</i> subsp. <i>sanguinea</i> and alien <i>C. alba</i>, <i>C. sericea</i> and <i>C. sanguinea</i> subsp. <i>australis</i> in the Southern Hemiboreal zone of Europe. Five sites for each of four taxa were selected for the study, and seeds were sampled using the soil core method (400 samples in two soil layers: the upper, 0–5 cm, and the lower, 5–10 cm). Extracted seeds were tested with tetrazolium chloride stain to assess their viability. Differences in the seed banks among taxa were compared using generalised linear mixed models (GLMM). The GLMM analysis revealed significant differences in soil seed bank densities in the upper soil between the studied taxa (<i>p</i> < 0.001). We found that two of the alien taxa (<i>C. alba</i> and <i>C. sanguinea</i> subsp. <i>australis</i>) formed a much denser seed bank containing more viable seeds than the native <i>Cornus sanguinea</i> subsp. <i>sanguinea</i>. All three alien species contained more viable seeds (from 40.7% to 45.2% in the upper soil layer) than the native <i>C. sanguinea</i> subsp. <i>sanguinea</i> (19.4% in the upper and 18.2% in the lower soil layer). The cover of <i>Cornus</i> and habitat type had no significant effect on the density of the seed bank, according to GLMM. This study supports the hypothesis that seed banks of alien <i>C. alba</i> and <i>C. sanguinea</i> subsp. <i>australis</i> are denser than those of native <i>C. sanguinea</i> subsp. <i>sanguinea</i>. Furthermore, the seed bank of alien taxa contained more viable seeds than the seed bank of <i>C. sanguinea</i> subsp. <i>sanguinea</i>. Results of this study contribute to the understanding of the invasiveness of alien <i>Cornus</i> taxa.