Early Life Stage Characteristics of Six Acadian Conifer Species: Germination and Seedling Development in a Changing Climate

Global climate change will drastically alter regional climates. The influence of these changes on the distribution and relative abundance of forest trees is both critically important and subject to substantial uncertainty. It will be particularly important to understand the effects of different climate scenarios on the early life stages of major tree species, because: 1) Early life stage performance and survival strongly influence the abundance of mature trees of a given species, 2) Trees are most sensitive to environmental variation during their early life stages, and 3) Our knowledge of the response of Acadian Forest tree species to environmental variation is very limited. In Experiment 1, we monitored the germination, growth, and development of six major Acadian Forest conifers: Abies balsamea, Picea glauca, Picea mariana, Picea rubens, Pinus strobus, and Tsuga canadensis. Seedlings were grown in two light environments: high light (60% of full sun), typical of canopy gaps, and low light (10% of full sun), typical of the understory beneath full canopies. In terms of germination, the Picea species germinated most rapidly and completely, P. strobus and A.balsamea germinated less completely and more gradually, and T. canadensis germination was strongly inhibited by higher soil temperatures associated with the high-light environment. Growth and biomass allocation varied widely among the six species. In the highlight environment, P. strobus and A. balsamea quickly developed extensive root systems, while the Picea species concentrated their growth on shoot development. In the low-light environment, A. balsamea maintained higher root allocation relative to the other species. In the high-light environment, the Picea species exhibited season-long neoformed shoot growth, while relatively early budset limited the shoot growth of the other species. In Experiment 2, we studied the relative sensitivity of P. rubens and A. balsamea growth and development to different light, soil moisture, and root competition treatments over the seedlings’ first growing season and the first two months of their second growing season. We found that the growth and development of both species was similarly sensitive to variation in belowground nutrient competition and soil moisture. So, any interspecific differences in the response of P. rubens and A. balsamea to dry conditions would probably arise due to differences in mortality rates during severely dry conditions rather than long-term growth effects of non-lethal variation in soil moisture. The results of Experiments 1 and 2 will provide insights into the relative fitness of these species in various climate change scenarios.