Coexistence Mechanisms Of Main Tree Species In A Broad-leaved Mixed Forest In The Taiyue Mountains, Shanxi, China

The 4 hm~2 deciduous broad-leaf forest plots were established in Taiyue Mountains following the protocols of the Centre for Tropical Forest Science forest dynamic plot. We tagged and recorded the species, diameter at breast height(DBH), height and crown diameter of all live and dead trees with DBH >1cm and revealed the population dynamics in this plot.In this study, we explored the contribution of density dependence to plant diversity in deciduous broad-leaf forest in warm temperate, tested the Janzen-Connell hypothesis, and analyzed the soil nutrient heterogeneity to research the mechanism of species coexistence in this plot.(1) The dominant populations were divided into three growth stages: saplings(1 cm ?DBH ? 10 cm), juveniles(10 cm < DBH ? 30 cm), and adult trees(DBH > 30 cm). Point pattern analyze in irregular area were used in this paper and removed the effects of environment heterogeneity. We determined the spatial distribution of six dominant trees and explore the effects of dead trees on their spatial patterns, the spatial distribution in different growth periods were measured by pair–correlation g(r) function. And our object was to explore the mechanisms generating and maintauining these patterns and reveal the population dynamics and the strategy of ecological adaptation and in this plot. The results were as follows: 9489 live individuals and 209 dead trees were recorded in this region. Quercus wutaishanica, Betuta playp Hylla, Carpinus turczaninowii, Acer mono, Crataegus cuneat and Pinus tabulaeformis with their ind, ividual number and overall highest importance value were the major dominant tree species. The spatial patterns of the population in this area are controlled by biotic interactions and local ecological characteristics, and the degree of aggregation weakens with its increasing DBH. The findings could well first simulate andpredict the density dependence in Taiyue Mountain.The pair–correlation g(r) function were used to examine the spatial pattern among different growth stages and by the methods of Bivariate random labeling and Case-control design to examine the distance effect of Janzen-Connell hypotheses and our object was futher to reveal the contribution of density dependence to plant diversity in deciduous broad-leaf forest in warm temperate. The result showed that the six main species in this plot have been influenced by the environment heterogeneity, and they were influenced by the density dependence effect in the process of different growth stage after excluding the role of habitat heterogeneity, nevertheless, the effects were not consistent throughout the whole life history.The distance effect of density dependence did almost not occur in the forest.(2)In order to test the Janzen-Connell hypothesis, the dominant populations were divided into saplings(1 cm ? DBH ? 8 cm) and adult trees(DBH > 30 cm).We classified the number of saplings and adult trees around an individual adult tree, and analysis the distribution of saplings from their big trees. The Neighborhood index was used to calculation the effects of individual saplings, adult tree and other trees to the samples. And the recruitment probability index in different scales was to reveal the relationship between an individual adult tree and the other trees. The result indicate that the Janzen-Connell hypotheses and the distance effect of Janzen-Connell were not an important mechanism influencing the species composition of this plot. However, around an individual adult tree, non-conspecific trees were far more abundant than conspecific trees.Although the mechanism for this p Henomenon is unknown, it real provided more space for the survival of other species and thus promoted species coexistence.(3) The SPSS17.0 was used to describe the soil nutrients in Taiyue Mountain, the theoretical semivariogram models for soil propertyand parameter values in the study area were measured by GS+(Version 7.0), and CCA method was used to investigate the relationship between plant species and soil nutrition to test the contribution of soil property to the species coexistence. The results were as follows: Among the seven soil indicators, the index varied between 27.37% and 56.35%, indicating a moderate variation. The nugget value of soil nutrition tested was weak, and the random factor played a dominant role. C0 /(C0+C)values of p H, O.M, Total N and Available K were more 80%, suggesting a strong spatialautocorrelation. The semivariance analysis indicated that Total P and Available P distribution in the upper and lower reaches of Taiyue Mountain can be well described by exponential model, Total N, Alkaline N, and O.M semivariance strueture Sp Hercial model. p H collaborative semivarianeeis Gaussian model, Available K is exponential model. And theoretical semivariogram models can well describe the spatial distrobution characteristics.The CCA ordination showed that Pinus tabuliformis related Total N and O.M, and there was a positive correlation between them, Crataegus cuneata, Quercus wutaishanica is negative correlation with Available P and p H, and there is a positive correlation with Available K.Betula platyp Hylla and Available P are closely related and were positively correlated.Carpinus turczanino was closely related to Alkaline N. This plant preference of different nutrient conditions inevitably affects their distribution in the community and they coexist in the community, and it is these different nutrient conditions that promote coexistence and the maintenance of the diversity of species in the study area.In conclusion, all the three parts of density dependence, Janzen-Connell hypotheses and soil nutrient heterogeneity had their contribution to the species coexistence. The density dependence, environment heterogeneity, Janzen-Connell hypotheses and soil nutrient heterogeneity provided support for the species coexistence on the community of Taiyue Mountains National Nature Reserve, and they contributed to maintain the plant diversity in the plot.