Relation between invasive plant and species richness of forest floor vegetation:: A study of Impatiens parviflora DC.

In 13 forest reserves situated in southern Poland, 68 study plots were established in two regions: the Jurrasic Upland and the Silesian Upland. In these plots, size 10 in x 10 in divided into 100 subplots 1m(2) each and randomly placed in various forest communities, percentage cover of all species in ground layer was recorded. Relationships between highly invasive alien plant species, Asiatic small balsam Impatiens parviflora DC., and indigenous species, was estimated using various indexes of species richness and diversity. They were: Hill's numbers (N-0, N-1, N-2),Shannon Wiener's index at the level of a subplot, alpha diversity (species richness within sites), and beta diversity (species richness among sites) at level of a study plot. The subplots with a presence of L parviflora were compared with those where only native resident species occurred. The study has shown that subplots with the occurrence of L parviflora are characterized by higher species richness and diversity of native plants independently on vegetation type. The frequency of L parviflora was negatively correlated with beta diversity of study plots but there was no association with values of alpha diversity. In oak forest, alder carrs and floodplain forests the negative correlation between percent cover of L parviflora and species richness, as well as cover of the herb layer was observed. The percent cover of L parviflora was positively correlated with number of native species in beech forest and with their total cover in mixed coniferous forests. However, in natural well-preserved forest phytocoenoses L parviflora avoids patches characterized by high cover of ground layer species and colonizes empty sites as an additional element of a community.