Abstract:

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 25 hm² forest plot of natural secondary forest of Quercus mongolica at Black-billed Capercaillie National Nature Reserve of national station in Heilongjiang province. The results showed that there were 10 species of vascular plants with DBH ≥1 cm in the plot， and 34 778 living trees with an average density of 1 392 trees·hm^-2. There were 4 species with important values of more than 10%， which were Quercus mongolica Fisch. ex Ledeb.，Betula dahurica Pall.，Betula platyphylla Suk.，Larix gmelinii（Rupr.） Kuzen successively， accounted for 89.65% of the whole plot. The Shannon-Wiener diversity， Simpson diversity and Pielou evenness index were 1.577， 0.760 and 0.685， respectively. The results showed that in this community， there were fewer rare species， larger proportion of common species than the others. What’s more， the community structure was simple. The average DBH of all tree species in the sample plot was 10.77 cm. The total diameter distribution in the community was of “reversed J type”， which was consistent with the distribution characteristics of typical uneven-aged forests. The diameter distribution of B.dahurica and B.platyphylla was approximately “reversed J type”， belonging to the growth populations， while the population of Q.mongolica showed a bimodal structure. The population of L.gmelinii was a declining species with an approximate normal size distribution and a tendency to disappear with succession. Under the CSR model， the spatial distribution of the four dominant populations was aggregation distribution and the degree of aggregation decreases with the increase of the scale， finally presenting a random or uniform distribution trend. Under the NS model， except L.gmelinii， the remaining 3 planted strains showed aggregation at 0-5 m scales， possibly influenced by the diffusion limitation of seeds. Comparing aggregation intensity of the four populations， it was found that B.dahurica＞B.platyphylla＞Q.mongolica＞L.gmelinii. Therefore， we might reasonably infer that the aggregation intensity of different populations was not only related to the scale of the study， but also to the population abundance.

Key words: Quercus mongolica, secondary forest, species composition, community structure, point pattern analysis