Natural regeneration of Norway spruce, an introduced species, in and around plantations in Quebec, Canada.
Introduced species are used more and more for timber production throughout the world. This raises much debate about their impact on natural ecosystems. In Quebec, Canada, similar concerns are expressed regarding Norway spruce (Picea abies (L.) H. Karst.), which was introduced in the early 1900s and is currently the main non-native conifer used for planting. The purpose of the present study was to evaluate the current spread of Norway spruce in Quebec and to assess under which circumstances it can regenerate and become established. We studied Norway spruce regeneration dynamics over 5 years in the understory, edge and surroundings of 10 thinned Norway spruce plantations aged 36 to 65 years. Most Norway spruce regeneration was found in the understory and near the edge of plantations, and beyond the plantation border on a few sites. Norway spruce seedling density was highly variable in the understory and at the plantation edge (0.6-30.7 stems.m-2 and 0-8.5 stems.m-2, respectively). Beyond the edge, high densities of Norway spruce regeneration (0.1 to 1.2 seedlings.m-2) were found in 2 recent clearcut areas and in only 2 intolerant hardwood high forests, as far as 28 m from Norway spruce plantations. Overall, Norway spruce regeneration was young (less than 16 years for 98% of seedlings) and relatively slow-growing (on average, 1.1-7.9 cm.year-1, depending on transect location and height class). Balsam fir (Abies balsamea (L.) Mill), a native species, regenerated well (mean density of 3.1 stems.m-2) in the understory and the edge of 5 of the 10 studied plantations. When regeneration of both species was present, mean seedling age, growth and height were similar, but balsam fir had a better survival rate than Norway spruce (84% vs. 65%). These findings suggest that Norway spruce shows a limited invasive capacity, particularly in the closed canopy of natural forests. Moreover, the presence of native balsam fir in the understory of Norway spruce plantations indicates that the successional pathway could move the stand towards a more natural ecosystem. These results can be useful to target surveys of the most sensitive ecosystems and to develop proactive management strategies.