| It is one of the main problems in ecology to study the spatial distribution pattern of species in plant communities,and to invert the mechanism of the pattern formation,so as to verify the hypothesis of the species coexistence and biodiversity maintenance mechanism.To explore the mechanism of species coexistence,biodiversity conservation and maintenance in ecotone of Daxing'an and Xiaoxing'an mountains,the community species composition,structural characteristics,size structure and spatial point pattern of dominant population were analyzed based on the data of 25hm2 forest plot of natural secondary forest of Quercus mongolica in the Heilongjiang Zhongyangzhan Tetrao parvirostris National Nature Reserve.The results showed that there were 36,338 free-standing woody plants with DBH?1cm in the plot,and there were 10 species of vascular plants,including 8 species of trees and 2 species of shrubs,belonging to 6 families and 9 genera.Among them,there were 34778 living trees with an average density of 1392 trees/hm2.Betula dahurica had the largest number of individuals,accounting for 31%of the total,and Quercus mongolica had the largestbasal area,accounting for 40.95%,and the largest important values,29.15%.There are 4 species which important values greater than 10%(Quercus mongolica?Betula dahurica?Betula platyphylla?Larix gmelinii),accounting for 89.65%of the total.The Shannon-Wiener diversity,Simpson diversity and Pielou index were 1.567,0.758 and 0.680,respectively.The results showed that the community had fewer rare species,larger proportion of common species and simpler community structure.The average DBH of all tree species was 10.77cm,and the largest plant was Quercus mongolica,whose DBH was 71cm.Larix gmelinii had the largest mean DBH(19.96cm).The total diameter distribution in the community was of "reversed J type",which was in line with the distribution characteristics of typical different-age forest.The diameter distribution of Betula platyphylla was approximately"reversed J type",belonging to the growth population.The population of Quercus mongolica had the largest number of individuals at 6cm diameter.The population of Larix gmelinii is a decaying species with approximate normal size distribution and a tendency of gradual disappearance with succession.Under different zero model tests and under different diameter-level structures,the spatial pattern is mainly manifested as the aggregation distribution,and the spatial distribution pattern is often closely related to the scale.The study of spatial distribution pattern of dominant population shows that with the increase of research scale,the population aggregation degree decreases gradually.With the increase of diameter level,the aggregation intensity of different diameter levels decreased,and the main reason may be that with the increase of diameter level,the plants' demand for environmental resources increased,the competition between species became more intense,and the self-thinning effect increased.From the analysis of spatial correlation,it can be seen that Betula dahurica and Betula platyphylla of the same genus have basically the same demand for spatial environmental resources,which leads to similar intra-specific correlation and strong negative correlation inter-species relationship.There may be a good synergistic effect between Quercus mongolica population and Betula dahurica,which is not related to Betula platyphylla population.Although the natural regeneration condition of Larix gmelinii is poor,the population has a strong positive correlation with Quercus mongolica and Betula dahurica,and coexists well on a large scale.The spatial resource utilization competition existed between Betula platyphylla population and Larix gmelinii population. |
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