Capacite de germination de trois especes exotiques et trois especes indigenes au Parc national du Canada Kouchibouguac, N.B., Canada

Plant introduction in new habitats can lead to ecosystem disturbance such as change in biodiversity, ecosystem services and functions and could cause negative impacts on human communities and their economy. It is essential to better understand mechanisms underlying success of exotic species in invaded habitats to effectively manage their presence in the environment. Exotic species can be a threat to ecological integrity in protected habitats such as in Kouchibouguac National Park of Canada. The goal of this study was to examine the germination strategies of three exotics species, Reed canarygrass (Phalaris arundinacea ), Purple loosestrife (Lythrum salicaria) and Dusty miller (Artemesia stelleriana) and three ecologically similar native species Bluejoint grass (Calamagrostis canadensis), Fireweed (Epilobium angustifolium) and Seaside goldenrod (Solidago sempervirens) in order to determine which germination and recruitment characteristics differed between native and exotic species that could give exotics a competitive advantage over native species. Burial depth, salinity and humidity levels as well as natural stratification were tested on seed germination in laboratory and recruitment was examined in natural habitats. In general, results are showing that exotic species have better and faster germination strategies under various conditions. All species, whether exotic or native, had better and faster germination on soil surface and germination rates decreased with increasing depth. Low humidity and high salinity levels had negative effect on rates and speed of germination for Dusty miller, Seaside goldenrod and one Purple loosestrife population. Interaction between these two factors was detected for Dusty miller and Seaside goldenrod indicating that both species reacted different ways to humidity when exposed to different salinity levels. Fireweed and Bluejoint grass germination rates were very low in laboratory and were different from those observed in literature under similar controlled conditions. Cold stratification did not seem to help increase germination rate for either species. Natural recruitment in natural populations seemed to show that exotic species had better and faster germination and better seedling survival than native species but population expansion seemed to depend more on vegetative reproduction than on sexual reproduction. In conclusion, germination strategies of studied exotic species could be one of many factors that may contribute to successful introduction in protected habitats, such as in Kouchibouguac National Park of Canada. Others factors should be analyzed to better understand exotic plant introduction, such as species ecology, interactions with others species and management action strategies. More research should be done on genetic and ecology levels to bring more knowledge and help Kouchibouguac National Park of Canada develop management plans to protect natural ecosystems.;Key words. Exotic species, germination, Phalaris arundinacea, Lythrum salicaria, Artemisia stelleriana, Calamagrostis canadensis, Epilobium cingustifolium, Solidago sempervirens, salinity, humidity, burial depth, recruitment.