| Based on analysis of main climatic factors, growth conditions, natural regenernation, species diversity difference between Pinus tabulaeformis Carr and Larix gmellini (Rupr.) Rupr communities, we evaluate stability of both communities synthetically and quantificationally with the Grey System Theory.The research results are summaried as follows:(1)The temperature measured in L. gmellini (Rupr.) Rup community was higher than P. tabulaeformis, and there is no significant difference of temperature between the different plots in the same community. In L. gmellini community, there was no significant difference of the air humidity among the different plots in the same community and the same altitude in two communities (P<0.05). With the altitude increasing, the light intensity in L. gmellini community increased. Among the three plots of P. tabulaeformis Carr community, the light intensity in bottom plot (N1) was highest.With the soil depth and altitude increasing, the indices value of physicochemical property of soil approximately decreased.Each indice value of physicochemical property of the same soil layer in the same altitude in the L. gmellini community was higher than the P. tabulaeformis community.(2)With the altitude increasing, the stand average DBH (diameter of a cross-section of a tree trunk 1.3 meters above the ground) decreased in L. gmellini community, but there was no difference of the stand average DBH in P. tabulaeformis community. The distribution of diameter class narrowed gradually in both communities. The distribution of diameter class of P. tabulaeformis is wider than that of L. gmellini and the DBH of P. tabulaeformis is bigger than that of L. gmellini.The L. gmellini community has a single hierarchy structure. It has a highly centralized main storey and is lack of saplings. The P. tabulaeformis community has a complex storey. The tree heights of P. tabulaeformis community are higher than that of L. gmellini community.At 10a, the growth rate of DBH and height in L. gmellini community began fast, and then that achieve the maximum growth rate at 20a. The average increment and current annual increment of DBH and volume of bottom plot (D1) in that community is highest, followed the medium slope plot (D2) and the last of that is the top plot (D3). Before 15 years ago, the growth of P. tabulaeformis was very slow. At 20a, the growth rate of height and volume in that community began fast.It achieve the maximum growth rate of DBH and height at 40a.The average increment of DBH of medium slope plot (N2) in that community is highest, followed the top plot (N3) and the last of that is the bottom plot (N1).Before 20a, the tree height grew at the rapid rate.The fast growing period of L. gmellini came early but was short, and that period of P. tabulaeformis came late but was long. The P. tabulaeformis community is more stable than the L. gmellini community.(3)The herb biomass of bottom plots in both communities was highest, followed the top plots and the last of that was the medium slope plots. The shrub biomass of the medium slope plot (N2) in P. tabulaeformis community was highest, followed the bottom plot (N1) and the last of that was the top plot (N3). The shrub biomass of the medium slope plot (D2) in L. gmellini community was highest, followed the top plot (D3) and the last of that was the bottom plot (D1). The tree biomass of N2 in P. tabulaeformis community was highest, followed N3 and the last of that was N1. The tree biomass of D1 in L. gmellini community was highest, followed D2 and the last of that was D3. The total and litter biomass had the same trend with the tree biomass of both communities. Except the N1 was lower than that of D1, the total biomass of P. tabulaeformis community at the same altitude was all higher than that of L. gmellini community.The herb biomass of P. tabulaeformis community at the same altitude was all higher than that of L. gmellini community. Except the shrub biomass of D1 was lower than that of N1, the shrub biomass of L. gmellini community at the same altitude was all higher than that of P. tabulaeformis community. Except the tree biomass of D2 was lower than that of N2, the tree biomass of L. gmellini community at the same slope sample was all higher than that of P. tabulaeformis community. The total biomass of P. tabulaeformis community at the same slope sample was all higher than that of L. gmellini community.(4)The stand of L. gmellini is the even-aged pure stands, and there were almost no seedlings in that community, so the natural regeneration was poor in this community. The structure of this community was not stable.The total density of seedlings of P. tabulaeformis community was more than that of L. gmellini community.The total density of seedlings of P. tabulaeformis community in N2 was highest, followed N1 and the last was N3.(5)The results indicated that the species distributed in shrub layer in two different communities are simila. Dominant herb species in P. tabulaeformis community was Dendranthema chanetii (Lévl.) Shih, and that in L. gmellini community were Carex ussuriensis.With the altitude increasing except for Alatalo evenness index, all the Alpha biodiversity indices of herb in P. tabulaeformis community first decreased and then increased, that of L. gmellini community reduce in different altitude.With the altitude increasing, Alatalo evenness index of herb layer of P. tabulaeformis community decreased, and that of herb layer of L. gmellini community increased first, and then decreased. Alpha biodiversity index of the both communities in the same altitude had no significant difference (P<0.05). With the altitude increasing, beta biodiversity index between plots of P. tabulaeformis community increased that between plots of L. gmellini community decreased. Beta biodiversity index between top plots of P. tabulaeformis and L. gmellini community was biggest.(6)The niche breadths of Saussurea pectinata and Poa nemoralis Linn. were higher than that of other species in L. gmellini community. Artemisia tanacetifolia, Lespedeza floribunda, Viola variegata Fisch. ex Link and N. cucullata (L.) Schltr. were using the similar environmental resource.The niche breadths of Carex ussuriensis and Setaria glauca (L.) Beauv. were higher in P.tabulaeformis community. The niche breadths of xerophytes in this community were wider. The trend of environmental succession is developing toward the climate arid. The niche overlap of Kalimeris lautureana (Debx.) Kitam. with Allium longistylum Baker and Carex ussuriensis were higher. With other species competing resources, K. lautureana (Debx.) Kitam. was vulnerable for interference.(7) By using the Grey System Theory analyzing the soil fertility, growth condition and herb diversity of both P. tabulaeformis and L. gmellini communities, the results were: the soil fertility of L. gmellini community was superior to the P. tabulaeformis community in the same altitude.Except the top altitude, the growth condition of L. gmellini community was superior to the P. tabulaeformis community in the same altitude. Except the medium altitude, the herb diversity of P. tabulaeformis community was superior to the L. gmellini community in the same altitude.By using the Grey System Theory, except the top altitude, the stability of L. gmellini community was superior to the P. tabulaeformis community in the same altitude.
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