珍稀植物对开蕨与其伴生物种的联结性及群落稳定性

基于2×2联列表,采用X2和W检验,联结系数(AC)、点相关系数(PPC)、Ochiai指数(OI)、共同出现百分率(PC)的种间联结性分析和M.Godron群落稳定性测定方法,以长白山极其狭小地区分布的国家Ⅱ级保护植物——对开蕨(Phyllitis scolopendrium)为研究对象,分析了其在海拔729、1008m群落内,对开蕨与其伴生种联结性及群落稳定性。调查显示:吉林省临江区域自然分布的对开蕨种群为小片状聚集分布,数量较少,局部大尺度上分布频度极低,为偶见种。与对开蕨伴生的植物共有70种,其中乔木16种,灌木16种,草本植物38种。联结性分析表明:群落总体联结性VR(方差比率)1,检验统计量WX20.05(N),显示群落种群间均表现出正关联,但没有达到显著水平。联结性测度指标显示对开蕨种群与乔木、灌木联结性低于与草本的联结性;其中对开蕨与乔木联结种对均不显著(X23.841);与灌木正联结种对以凤城卫矛(Euonymus maximowiczianus)达到显著正联结(X23.841),其它联结均不显著;对开蕨与草本植物三叉耳蕨(Polystichum tripteron)达到极显著正联结(X26.635),与粗茎鳞毛蕨(Dryopteris crassirhizoma)为显著正联结,与野芝麻(Lamium barbatum)为显著负联结(3.841X26.635),反映出对开蕨与大多数植物种群关联不显著或显著关联的种群极少,种间联结关系较为松散趋向于相互独立,有很大的随机性。群落稳定性测定得出:海拔1008m的01群落和海拔729m的02群落,其总体的累计种类倒数百分数与累积相对频度比值分别为35/65、34/66,均远离20/80;各群落内乔木层、灌木层、草本层的比值也远离稳定点坐标,显示出群落总体均不稳定;两个群落内部各层次的稳定性排序均为草本层灌木层乔木层。结论提示:现存对开蕨群落极不稳定,亟待加强保护。在物种保护和回归实践中可通过保护和选择与之正联结较强的物种来保护和建立对开蕨生存环境以求对开蕨分布群落的稳定,最终达到实效保护目的。

Analyses of community stability and inter-specific associations between the rare plant Phyllitis scolopendrium and its associated species

The fern Phyllitis scolopendrium (Aspleniaceae) is listed as a secondary protected plant in China. The species is extremely rare, and its distribution is limited to Changbai Mountain along the border with North Korea. Nearly nothing is known about its ecology, except for scarce studies on its artificial culture. The results of our previous field survey show that the natural population of P. scolopendrium has an aggregated distribution within a very limited area, and only few individuals are found in the Linjiang area of Jilin Province. A total of 70 plant species were found to occur near P. scolopendrium, including 16 species of trees, 16 species of shrubs, and 38 species of herbs. In the present study, we examined the inter-specific associations of this fern with other plant species and their relationship with community stability. On the basis of a 2 × 2 contingency table, we used a set of different methods, namely, X² and W tests, association coefficient, point correlation coefficient, Ochiai index, and percentage co-occurrence, to analyze the inter-specific associations between P. scolopendrium and co-occurring species. In addition, we tested the level of community stability at elevations of 729 m and 1008 m by using the Godron stability analysis. The results showed that the total community association of variance ratio was greater than 1; the test statistic W was lower than X_{0.05 (N)}², indicating that the species in the overall community were positively associated (although this association was not significant). An analysis of association indices revealed that P. scolopendrium was less strongly associated with trees and shrubs than with herbs. When species pairs were analyzed, the association of P. scolopendrium with trees was not significant (X² < 3.841), its association with the shrub Euonymus maximowiczianus was significant (X² > 3.841), and all other associations analyzed were not significant. For herbs, the association of P. scolopendrium with Polystichum tripteron was strongly and significantly positively correlated (X² > 6.635), that with Dryopteris crassirhizoma was significant, and the association with Lamium barbatum was significantly negatively correlated (3.841 < X² < 6.635). These results indicated that there were no significant inter-specific associations between P. scolopendrium and most co-occurring plant species. With the exceptions of a few shrubs and herbs, inter-specific correlations tended to be independent and random. Godron stability analysis showed that the ratios of cumulative inverse of species number to cumulated relative frequency of two plant communities at 1008 m and 729 m of elevation were 35/65 and 34/66, respectively, distinctly different from 20/80. The ratios of the arbor layer, shrub layer, and herb layer in each community were also far from the stability point, indicating that the whole community was unstable. The stability ranking within each community was herb layer > shrub layer > tree layer. These results indicated that the P. scolopendrium community is not stable, and stronger protective measures are required. For species protection and ecological recovery, species with strong positive associations should be chosen for protection in order to establish a suitable environment for P. scolopendrium, stabilize its population, and effectively protect this rare species.