Factors Influencing the Germination, Emergence, and Early Survival of Boreal, Temperate and Exotic Acadian Forest Tree Species in Central Maine

Climate is thought to play a primary role in determining the geographic range limits of plants. Maine\u27s Acadian forest contains many commercial tree species that are close to the limits of their natural distributions. Thus, there is interest in how anticipated changes in climate may influence Maine\u27s forests. Although the critical factors that limit the ranges of most tree species are currently unknown, trees are often most sensitive during their early life stages. These early life stages have not been extensively studied in Maine\u27s Acadian forest. The objectives of this thesis were: 1) quantify the effects of temperature and moisture regime on germination success and germination phenology of native tree species that are close to their range limits in Maine as well as common introduced tree species, 2) quantify the effects of predator protection, sowing date, grass competition, and overstory canopy on emergence, emergence phenology, and survival during the first growing season of tree species that are close to their range limits in Maine as well as common introduced tree species, and 3) determine if silviculture might be used to mitigate negative effects of climate change to promote regeneration of desired tree species. Tree species used in this study represent boreal (balsam fir, white birch and trembling aspen) temperate (red maple, red spruce and eastern white pine) and exotic (Norway maple, hybrid larch and Norway spruce) groups. A growth chamber study (Chapter 2) was used to examine the effects of temperature and moisture regime on germination (Objective 1). Results indicated that moisture availability was primarily responsible for level of germination success. Germination success under moderate and high levels of moisture stress varied among species. Trembling aspen germination was most tolerant of moisture stress. Red spruce and hybrid larch were tolerant of moderate moisture stress at cooler temperatures, but not of high moisture stress. Norway spruce, white birch, and eastern white pine were moderately tolerant of moderate, but not high moisture stress. Balsam fir and red maple were least tolerant of moisture stress. Germination phenology varied among species and was influenced by temperature and moisture. A field study was conducted during 2004 at the Penobscot Experimental Forest near Eddington, Maine to address objectives two and three (Chapter 3). Predator protection and sowing date were the primary factors influencing emergence success for the majority of species. The effects of these factors varied with species. Predators avoided balsam fir; predation losses of the remaining species increased with seed mass. Fall sowing favored or did not affect boreal species, did not affect temperate species, and was detrimental to exotic species. Grass competition and overstory became more important after seedlings emerged. Grass competition reduced survival of all species. Overstory reduced survival of hybrid larch and white birch. Emergence phenology varied among species, but was relatively insensitive to the treatments. Except for sowing date, responses to treatments in both studies did not correlate with the species groups. These results suggest that if climate modifies the factors examined, Acadian tree species will respond individually, rather than what would be predicted based on their current geographical distributions