Abstract
This paper describes the alien vascular plant flora in the Lake Engure Nature Park, one of the most species-richest and diverse areas in Latvia. The review was based on the floristic inventories conducted in 1983-1989 and a field survey carried out in 2010. In total, 68 alien species (7.6% of the vascular plant flora in the nature park) were recorded, of which four had established in the period between both surveys. 22 species were recognised as adventive species and 46 as escaped species. Most of the alien species area concentrated in coastal villages, around human settlements, roadsides, coastal dunes and along streams discharging in the Lake Engure, thus mostly in transformed habitats. They are absent in most of the natural and semi-natural habitats. In comparison to the overall situation in Latvia, the Lake Engure Nature Park area is relatively little affected by plant invasions, most probably because large areas of natural and semi-natural habitats remain, since high naturalness of vegetation plays a significant role as a natural barrier hindering alien invasions.