Abstract:

Based on the study on the history of fire disturbance at landscape scale in virgin forest in northern of Daxing'an Mountains, this paper studied the cohort structure of Larix gmelini population and its relations to the fire disturbance and site. The cohort structure based on the number of cohort of Larix gmelini population was rich, and there were 6-groups from the group of 1-cohort to the group of 6-cohort with patch-mosaic distribution in landscape. The group of 3-cohort and the group of 4-cohort being the main type were aggregated in space,while the others were heterogeneity in space. The fire frequency, fire intensity and their synthetical regime influenced the number of cohort strongly, while the effect of fire intensity was more significant. The fire of low frequency or high intensity increased the number of population cohort, however that of high frequency or low intensity decreased the number of cohort. In addition, there was different number of cohort among different forest type groups. The number of cohort showed such: group of nearby stream > group of Alnus mandshurica> group of Ledum palustre. The cohort structure based on the fire disturbance regimes was also abound, and there were 3groups, 6 sub-groups, and 12 types in patch mosaic. The sub groups of regeneration cohort dominance & pre fire cohort inferiority and the sub type of pre fire cohort dominance & regeneration cohort inferiority being the main sub type distributed aggregately, while the others were of high spatial heterogeneity. The cohort structure was intensely affected by fire frequency, fire intensity and their synthetical regime. The fire frequency was advantage to the dominance cohort,while the fire intensity controlled the inferiority cohort. There were sub-groups of regeneration cohort dominance & pre-fire cohort inferiority on site of low frequency or high intentisy sub-groups of regeneration cohort dominance & post fire cohort inferiority on site of middle frequency or middle intensity, and sub-groups of pre-fire dominance & post fire cohort inferiority on site of high frequency or low intensity. The group and the sub-group of cohort structure changed with site. Both the sub-groups of cohort structure on site of the group of nearby stream and the group of Alnus mandshurica were sub-groups of regeneration cohort dominance & pre-fire cohort inferiority, but that on site of the group of Ledum palustre was a sub-group of regeneration cohort dominance & post-fire cohort inferiority. There was sub-groups of regeneration cohort dominance & pre-fire cohort inferiority on site toward east, while sub-groups of pre-fir cohort dominance & post-fire cohort inferiority on site toward west and north. There were 224 forest compartments, being groups of regeneration cohort dominance while being groups of pre-fire cohort dominance 218forest compartments.

Key words: Daxing'an Mountains, Virgin forest, Population of Larix gmelini, Structure of generations, Fire disturbance, Site