The Study Of Ecological Structure And Development Of Natural Secondary Forest Communities Of The North China Mountainous Area

In this research, we conducted the natural Populus davidiana-Betula platyphylla secondary forest communities of North China in Rocky Mountain Area. As the native species, after the severely damage course by different levels of human disturbance and following decades of natural recovery, Larix principis-rupprechtii communities have been gradually replaced by Populus davidiana-Betula platyphylla secondary mixed communities which has been the typical transition communities of the zonal vegetation natural restoration and succession process in that region. The study chose Populus davidiana pure stand, Betula platyphylla pure stand, and their mixed stand with different mingling degree, analyzed the dominant populations structure, niche, biological diversity and spatial distribution patterns in different communities, moreover, compared their near natureness and stand dominance, analyzed the development trend of natural Populus davidiana-Betula platyphylla secondary forest in the region. The main findings are as follows;(1) The stand density of natural secondary forest communities was relatively large, and the species was abundant which total11tree species were included. In these communities, dominant species Populus davidiana and Betula platyphylla account the absolute weight, with the main associated tree species were Larix principis-rupprechtii, Acer truncatum and Picea asperata. Four hectare standard plots contained a Populus davidiana community (A plot), a Populus davidiana community (B plot), and two Populus davidiana-Betula platyphylla mixed communities with different mingling degree (C1, C2plot). Plot A had the largest stand density,853trees/hm2, and the smallest was plot C2with572trees per hectare; the basal area of plot C1was the largest, followed by plot A, the basal area of Populus davidiana, Betula platyphylla and Larix principis-rupprechtii occupied the absolute advantage; the diameter class structure were relatively typical, Populus davidiana and Betula platyphylla populations were basically presented single peak curve, the associate tree species in different communities were presented reverse J curves; the vertical stand structure were different in each communities, excluding the Populus davidiana community, the others were presented bimodal curve with obvious stratified.(2) In the study area, the arbor and shrub populations had even niche breadth distribution. Larix principis-rupprechtii, Acer truncatum, S. pohuashanensis, Bemla platyphylla were relatively larger in arbor layer, and Betula dahurica. Betula costata, Pinus tabulaeformis were smaller; larger niche breadth in shrub layer were Acer truncatum, Corylus mandshurica and Swida bretchneideri, and Viburnum dilatatum, Berber is amurensis, Lonicera tatarinowii were relatively smaller in niche breadth. The populations of dominance in niche also had higher overlap, in arbor layer, Sorbus pohuashanensis, Acer truncatum, Quereus mongolica and Picea asperata were the main association tree species in Populus davidiana-Betula platyphylla forest, and that Corylus mandshurica and Corylus mandshurica were the dominant species in shrub layer which Swida bretchneideri and Weigela hortenis appeared as the main association species.(3) compared the three type a diversity indicators of natural secondary Populus davidiana-Betula platyphylla forest, the herb layer was significantly higher than the shrub layer and arbor layer, but there was not obvious differences between the shrub layer and arbor layer. In species richness and diversity, shrub layer was slightly higher than the arbor layer while the evenness index was opposite slightly lower, indicating that the shrub layer diversity was not high in differentiation due to the huge density of Acer truncatum and Corylus mandshurica which occupied throughout the shrub layer of community. Comparing the different type of communities, the arbor layer biodiversity of mixed communities were significantly higher than Populus davidiana community and Betula platyphylla community, while in the shrub layer, Betula platyphylla community had the highest biodiversity, followed by mixed communities. Populus davidiana community was the lowest biodiversity in shrub layer but highest in herb layer, which followed by mixed communities and Betula platyphylla community.(4) According to the results of point pattern analysis, the main populations of each community in natural secondary forest were showing the aggregative distribution in different levels, which of the respective different trends with different scales. In the relationship between species, except smaller scale, the dominant Populus davidiana and Betula platyphylla populations showed a significant negative correlation with Larix principis-rupprechtii population in all scales among r<25m, intense competition; in addition to showing a significant negative correlation with Populus davidiana population, Betula platyphylla population was positively correlated with Larix principis-rupprechtii population. Only in B plot was Betula platyphylla population negatively correlated with Larix principis-rupprechtii population, and showed non-significant correlation with Quercus mongolica.(5) Analysis of the near natureness and stand dominance of different natural secondary forests provided an order of near natureness:C2plot> B plot> Cl plot> A plot, and an order of stand dominance:C2plot> Cl plot> B plot> A plot. According above it could be clear that the mixed Populus davidiana-Betula platyphylla community was more closer to natural steady state and more vigorous than respective pure stands for growth.(6) Based on the above data, analyzing the ecological structure comprehensively, it could be concluded:the structure of Populus davidiana population was relatively poor, the arbor and shrub layer were of low biodiversity, the population restorage was slow, and it emerged a large area dead wood phenomenon meantime, showing the pessimistic prospectation for the population; Betula platyphylla population was slightly better with its more young trees and relatively strong viability, which were able to maintain its dominance in a given period; compared to those, the mixed stand was the optimal with the relatively better stand structure, dominance and near natureness, as well as the stability of all other stands. As a pioneer species of secondary succession, natural secondary Populus davidiana-Betula platyphylla forest of North China in Rocky Mountain Area had entered a medium-term of succession, considering the seedling regeneration, the emerged of large number of secondary climax species Acer truncatum seedlings suggested it would gradually become the major dominant species and constructive species in that region, moreover, it would gradually form an Acer truncatum secondary climax community, and ultimately developed to Pinus tabulaeformis and Larix principis-rupprechtii climax community.