中文摘要：

在景观火干扰历史重建的基础上，该文研究了大兴安岭北部地区原始林白桦（Betula platyphylla）种群的世代结构及其与火干扰、立地条件之间的关系。结果表明：白桦种群基于世代数的世代结构类型丰富，从一代型到五代型都有，空间分布呈斑块镶嵌状。以一代型与二代型为主要类型，空间分布集中，其它类型的世代结构空间异质性较高。世代数受火干扰频率、火干扰强度及两者的综合影响，相对来说以火干扰频率的影响更为显著。低频或高强类的火干扰易造成种群的世代数减少；高频或低强类的火干扰易造成世代数增多。世代数还随林型组类型而变化，以溪旁林组〉赤杨（Alnus mandshurica）林组〉杜香（Ledum palustre）林组。 白桦种群基于火干扰的世代结构类型也很丰富，存在3大类、5亚类和11小类，空间分布呈斑块镶嵌状。其中以火后优势火前劣势型和更新优势火前劣势型为主要类型，空间分布较聚集，其它类型的空间异质性较高。这种世代结构也受火干扰频率、火干扰强度及两者的综合影响。随着火频增高或者火强减弱，白桦种群的自我恢复性和抗火性增强，火后恢复性减弱。中高强火烧地上，世代结构为火后优势火前劣势型，低强火烧地上为更新优势火前劣势型。世代结构还随立地条件而变化。不同林型组之间，白桦种群的优势世代（火后代和更新代）存在显著的数量差异，但是世代结构保持为火后优势火前劣势型；偏东坡为火后优势火前劣势型，偏西坡及北坡为更新优势火后劣势型；224林班为火后优势型，218林班却为更新优势型。

英文摘要：

Background and Aims Natural fire is a frequent driving force of communities and populations. However, the cohort structure of Betula platyphylla in the virgin forest of the northern region of Daxing＇ anling Mountains, China, has rarely been studied. The aim of this paper is to explore the abundance, type and spatial distribution of the cohort structure of B. platyphylla, based on the number of cohorts, the fire regime and their relationship to site factors. Methods We used an integrative approach to statistically analyze natural fire disturbance and population structure of B. platyphylla. Data on fire disturbance and population structure were collected from 96 plots distributed throughout the landscape. Fire history at the landscape scale was reconstructed based on tree regeneration and fire scars. Population cohort structure was recognized based on the number and regeneration type of cohorts identified. Key Results Cohort structure based on the number of cohorts is diverse, consisting of one through five cohort groups with a patch-mosaic distribution in the landscape. The main type, i.e., groups with one and two cohorts are aggregated in space, while the others have a heterogeneous distribution. The number of cohorts is influenced by fire frequency, fire severity and their interaction, but the effect of fire frequency is greatest. Fires of low frequency or high severity increase the number of population cohorts, while fires of high frequency or lowseverity decrease the number of cohorts. In addition, the number of cohorts differs by forest type, with the number of cohorts decreasing from the forest type near streams to the type with Alnus mandshurica to the type with Ledum palustre. Cohort structure based on regeneration type is also diverse, with three groups, five subgroups and 11 types distributed in patch-mosaic. The main sub-types, i.e., post-fire cohort dominance and pre-fire cohort inferiority and regeneration cohort dominance and pre-fire cohort inferiority, are distributed aggregately, while the o