| In order to clarify the characteristics of plant community under plantation and to improve the structure of three typical low-function plantations, i.e., Pinus tabuliformis forest, Robinia pseudoacacia forest, Platycladus orientalis forest in Beijing. A total of 34 sampling sites were set up in low mountain areas to conduct coenological investigation. The distribution pattern of undergrowth species, interspecific relationship and the relationship between understory community and environmental factors were analyzed by niche theory, interspecific association, canonical correspondence analysis and grey incidence analysis. This study was aimed to give scientific basis for the management of forests and diversity conservation. The results were as follows:(1) There were 111 kinds of species in the study area including 26 shrubby plants and 85 herbaceous plants which belonging to 88 genera and 47 families. The majority of them were Compositae, Gramineae, Liliaceous, Rhamnaceae and Leguminosae. Vitex negundo var. heterophylla, Grewia bilob, Rhamnus parvifolia, Ziziphus jujuba var. spinose, Lespedeza floribunda were dominant species in shrub layer under three plantations in Beijing, and Carex lanceolate, Cleistogenes caespitosa, Rubia cordifolia, Selaginella sinensis, Artemisia sacrorum were dominant species in herb layer, for their niche breadth was larger.(2) Most species having high niche breadth were inclined to produce a niche overlap with others. A few species with narrow niche breadth might have a great niche overlap under the pressure of limited environmental resources. The niche overlap value of a species pairs may be various in different community environments. This phenomenon may be due to the amount of available resources and the distribution pattern of species.(3) Few species pairs showed significant association and most of them had negative association, demonstrating that the interspecific relationship among undergrowth was quite loose, especially the distribution of herbaceous species was relatively independent. It was indicated that the understory vegetation community under three typical low-function plantations situated at prior or middle succession stage. And there was a highly significant positive correlation between the association coefficient AC and niche overlap, i.e., the greater the association coefficient, the higher the niche overlap.(4) The two set of environment variables (forest growth factors and topographic features) had overlapping effect on the distribution pattern of undergrowth species, and topographic factors had greater effects. Canopy density, slope aspect, slope, stand density and altitude had significant effect on shrubby species distribution with the impact intensity decreasing, while altitude, slope aspect, canopy density, tree height and stand density had significant effect on herbaceous species distribution.(5) The difference of Pielou evenness index in shrub communities under three plantations was not significant, and that of four community diversity indexes in herb communities were also insignificant. Grey incidence analysis was used to elucidate the relationship between understory vegetation diversity and environmental factors. It was showed that slope was the main factor affecting community diversity among these environmental factors, and its grey correlation coefficient with diversity indexes was in the range of 0.65～0.85, belonging to a strong correlation.The undergrowth of three low-function plantations in the study area was still far away from the state of climax community. To promote the successional development of the undergrowth, species with specialized ecological niche and species pairs with significant positive association should be protected at present. Based on the environmental factors significantly affecting the distribution of species and the variation of community diversity, the article approves some suitable.species for different wood lands to optimize the structure of plantations. |
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