Lodgepole pine (Pinus contorta Doug.) shows low self-regeneration and dispersal in Latvia

Considering the high invasiveness of lodgepole pine (LP, Pinus contorta Dougl.) in parts of its introduced range, concerns about invasion risks in the Baltic region have been raised. In this regard, self-regeneration, dispersion distance, and factors affecting LP regeneration outside plantations were studied in Latvia, where the species is still considered as an alternative for forest regeneration. Among the 20 plantations investigated, 45% contained seedlings or saplings of LP. The density of LP within and in proximity to the plantation (up to 90 m) was similar, at 240 ± 78 and 234 ± 103 seedlings ha -1 , respectively. The assessed LP plantations were still young (28 to 47 years), which might have contributed to lower pressure of propagules on the surrounding area, as the most distant seedling was found at 89 m. Site properties affecting LP regeneration included the absence of large canopy openings and bare soil, lack of competition, and, particularly, high browsing damage (24%) on seedlings over 30 cm. The regeneration densities and biotic limitations suggest that the invasion risk of LP in Latvia is currently low, nevertheless, monitoring of dispersal is still needed.