Is early life cycle success a determinant of the abundance of red spruce and balsam fir?

Abstract

Red spruce ( Picea rubens Sarg.) and balsam fir ( Abies balsamea (L.) Mill.) are sympatric in much of the Acadian Forest, but their relative regeneration success during the changing climates of the Holocene and after harvest in the modern forest has been distinctly different. Early life stage behavior may contribute to these differences. We report that seed germination by red spruce was equally fast and complete in warm and cool temperature regimes, while balsam fir germination was slower and less complete in both, especially the cool regime. Also, seedling shoot growth of red spruce exhibited a highly plastic response to increased light and water by maintaining continuous neoformed growth throughout the growing season, while balsam fir seedlings set bud after very little epicotyl development. Therefore, the root/shoot ratio of balsam fir was about twice that of red spruce, regardless of available light or water. Neoformed shoot growth under conditions of ample moisture and light would give red spruce a competitive advantage, but the relatively high root/shoot ratio of balsam fir seedlings would lower the likelihood that water and (or) mineral nutrients would limit shoot growth. The effects of these and other differences in life stage behavior on species abundance over time are discussed.