Disturbances can interrupt feedbacks that maintain stable plant community structure and create windows of opportunity for vegetation to shift to alternative states. Boreal forests are dominated by tree species that overlap considerably in environmental niche, but there are few tests of what conditions initiate and sustain different forest states. Here, we examine patterns of post‐fire growth and density of tree seedlings in early succession and use structural equation models to estimate relative effects of environmental and pre‐fire conditions, fire characteristics, and biotic interactions. We surveyed tree seedling recruits for 13 yr across a broad range of environmental and fire conditions (n = 89) in Alaskan black spruce stands that burned in 2004. Densities of established seedlings at 13 yr were strongly determined by initial recruitment that occurred within 2 yr after fire. High proportional combustion of the soil organic layer (fire severity) led to increased densities of deciduous seedlings but not of black spruce and had a positive influence on aboveground biomass of all species. Biotic interactions such as mammalian herbivory or woody competition, potential mechanisms for relay floristic succession, had no detectable effects on tree seedling densities or biomass. Repeated surveys instead suggested persistent shifts in successional trajectories of tree communities from spruce to deciduous dominance at sites where high fire severity created positive conditions for deciduous seedling recruitment and growth. Unless future species interactions alter the deciduous dominance of tree seedling composition, the vegetation transformations that we observed in response to high fire severity are likely to persist over the short fire cycle that increasingly characterizes the fire regime of Interior Alaska.

中文翻译：

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构成阿拉斯加黑云杉林火烧交替演替轨迹的因素

干扰会中断反馈，从而保持植物群落结构的稳定，并为植被转变为替代状态创造机会之窗。北方森林以树木为主导，树木在环境生态位上有很大重叠，但是很少有关于什么条件引发和维持不同森林状态的测试。在这里，我们研究了早期演替后树苗的火后生长和密度模式，并使用结构方程模型来估计环境和火前条件，火的特征以及生物相互作用的相对影响。我们在广泛的环境和火灾条件下调查了13年的树苗新手（n = 89）在2004年燃烧的阿拉斯加黑云杉林中。13年生苗的密度主要由火灾后2年内的初次招募来确定。土壤有机层的高比例燃烧（火势）导致落叶树苗密度增加，但黑云杉则没有，并且对所有物种地上生物量都有积极影响。生物相互作用，例如哺乳动物的草食性或木本竞争，中继植物区系演替的潜在机制，对树木的幼苗密度或生物量没有可检测到的影响。相反，反复的调查表明，在高烈度为落叶树苗的募集和生长创造了积极条件的地点，树木群落的演替轨迹从云杉向落叶树种的主导地位持续变化。