Studies On The Community Structure And Dynamics Of Typical Coniferous And Broad-leaved Mixed Forests In Changbai Mountain Region

The original broad-leaved Korean pine forest is the zonal climax vegetation type in the Changbai Mountain. Since the20th century, the resource of original broad-leaved Korean pine forest has been seriously damaged in Changbai Mountain, resulting in a large area of secondary forest communities. The conservation of original broad-leaved Korean pine forest and restoration of degraded secondary forest community is extremely urgent. Based on three large permanent forest dynamics plots in the Changbai Mountain region, the community structure and dynamics of the original broad-leaved Korean pine forest and secondary forests at different successional stages in Changbai Mountain were studied, the differences between the variations of community structure and dynamics between the forests were compared at the temporal and spatial scales to explore the possible factors which influence the forest structure and population dynamics, and try to reveal the succession laws and broad-leaved species coexistence mechanisms.The number of woody plants with DBH≥1cm in secondary poplar-birch forest(PBF), secondary mixed conifer and broad-leaved forest(CBF) and Tilia-Korean pine forest(TPF) were19673(15families,26genera,45species),14662(12families,21genera,38species) and11526(10families,13genera,22species), with an average diameter of5.6cm,7.4cm,10.1cm, respectively. The total basal areas were23.95m2/hm2,32.15m2/hm2and55.47m2/hm2. The size structure distribution showed inversely J-shape. In the process of secondary forests succeeding to the climax community, the DBH class structure of the Pinus koraiensis, Tilia amurensis, Acer mono and the main pioneer species Populus davidiana and Betula platyphylla had a tendency to the larger sizes.The majority of species showed aggregated distribution at small scales(1～20m)in all three plots. Acer barbinerve and Acer mono are positively correlated at all scales, which provd that the two maple trees can coexist in the community. The Tilia amurensis and Populus davidiana were good companion tree species, but Betula platyphylla is negatively correlated with most major trees, thus it gradually withdraw from the community in the succession process. The species with similar niche compete stronger because of similar demand for the resource. And the same species may have different interspecies associations in different sites. Habitat heterogeneity and different competitive pressure may be the reasons why most of species showed distinct spatial patterns in three plots.Different sampling designs had a significant impact on species-area relationship. In both sampling methods, the minimum area size order was:secondary poplar-birch forest<secondary mixed conifer and broadleaved forest<Tilia-Korean pine forest. According to AIC values, the logistic model based on random sampling method is the optimal model to fit the species-area relationship of mixed conifer and broadleaved forest in the three5.2hm2plots in Changbai Mountain, especially fit best for secondary poplar-birch forest at the initial stage of succession, followed by secondary mixed conifer and broadleaved forest and Tilia-Korean pine forest.From the recensus in five years, the second poplar-birch forest had the number of individuals with DBH≥1cm from19673to22399, the number of species increased13species. Accordingly, the secondary mixed conifer and broad-leaved forest had14662to15074individuals and the species added by10, while the original broad-leaved Korean pine forest reduced the number of individuals from the11526to9800.29of45,7of38and2of22species in the three corresponding forests plots had increased the individuals by the end of recensus.With the increase of DBH, the populations increased the radial growth and decreased the mortality, and the reversed the tendency across the larger size class. The size distribution of dead trees after the recensus showed a reverse J shape to, as well as the overall size distribution in the plots. Most of the dead individuals are less than4cm DBH, taking a percentage of88.6%,72.8%and68.3%of all dead individuals in respective forests. Negative density dependence and neighborhood competition were the main mechanisms that influenced the mortality of individuals, especially the small ones.The second poplar-birch forest is more dynamic than the other two forests, with a faster radial growth, recruitment and population growth. The original broad-leaved Korean pine forest has the highest mortality rate, and the population growth declined and showed regression. While the secondary mixed conifer and broad-leaved forest has the low population growth and mortality, and was the most stable communities among the three plots. As the succession of forests, the importance of Pinus koraiensis, Tilia amurensis and Abies nephrolepis enhanced; the importance of species, for example, Quercus mogolica, Populus davidiana and Betula platyphylla, and so on, decreased in the forests. According to the secondary succession theory, the Pinus koraiensis and Tilia amurensis will replace the light demanding species of Populus davidiana and Betula platyphylla in the forests as the death of pioneer species and development of dominant species. The secondary forests will get to more stable stage in the future.