柏木低效林不同改造模式优势草本植物多样性及其生态位

草本层对森林生态系统具有重要的作用,其对于环境的变化比乔木层和灌木层更为敏感,在较短的时间内更容易反映改造带来的影响。为了分析林分改造后草本植物多样性的变化和揭示草本群落间的关系,以川中丘陵区改造4 a后的11种模式:不同密度(株行距1.5 m×4 m与1.5 m×2 m)的桤木(Alnus cremastogyne)、香椿(Toona sinensis)、银木(Cinnamomum septentrionale)纯林模式和株行距为1.5 m×2 m的银木+桤木模式、香椿+银木模式、香椿+桤木模式、桤木+香椿+银木模式以及采伐迹地作为研究对象,柏木(Cupressus funebris)纯林为对照,对柏木低效林不同改造模式的优势草本植物多样性、生态位宽度及生态位重叠进行研究。结果表明:(1)除高低密度香椿模式、低密度银木模式和桤木+香椿+银木模式外,其他模式的草本植物多样性均优于柏木纯林,其中以香椿+银木模式(Shannon-Wiener指数、Simpson指数、均匀度和丰富度指数分别为(1.82、0.83、0.94和1.30),与香椿+桤木模式(1.83、0.83、0.93和1.33)的生物多样性显著高于柏木纯林(1.48、0.69、0.82和1.27),为最优的改造模式。(2)改造前铁线蕨(Adiantum capillus-veneris)生态位宽度最广为2.365,喜阴植物占有优势地位,改造后林下光照环境发生变化,喜阳植物五节芒(Miscanthus floridulus)在低密度的纯林模式中迅速占据林下生长空间,生态位宽度较大,随改造模式郁闭度的增加,薹草(Carex tristachya)、地果(Ficus tikoua)、竹叶草(Oplismenus compositus)等喜阴植物逐渐占据优势地位,喜阳植物逐渐被淘汰。生态位宽度的大小与重要值呈极显著正相关关系(r=0.916),但也与资源位呈极显著正相关关系(r=0.977)。(3)生态位宽度较大的物种间既有较大的生态位重叠,也有较小的生态位重叠,不能仅凭生态位宽度来判定生态位重叠值,而生态位宽度较小的鼠麴草(Gnaphalium affine)(0.647)与蛇莓(Duchesnea indica)(2.152)之间拥有最大的生态位重叠(0.123),可能是因为它们有相似的资源利用方式或相近的生态学特性。总体来说所有模式中草本植物物种间生态位重叠值都较低(0.2),生态位分化明显,种间竞争并不激烈,这可能与改造时间较短有关系。

Study on plant diversity and niche characteristics of dominant herbaceous populations under different reconstruction patterns in low efficiency stands of Cupressus funebris

Herbaceous layer plays a very important role in a forest ecosystem; it is more sensitive to environment than the arborous and shrub layers. Changes in herbaceous communities are more likely to reflect the effects of transformation in a relatively short period. To analyze the diversity of herbaceous plants after reconstruction and reveal the ecological relationships of herbaceous communities, pure forest plantations of Cinnamomum septentrionale, Alnus cremastogyne, and Toona sinensis and mixed plantations of C. septentrionale + A. cremastogyne, Cinnamomum septentrionale + T. sinensis, T. sinensis + A. cremastogyne, and C. septentrionale + A. cremastogyne + T. sinensis were studied The cutting-blank were selected as the research object, whereas the pure C. funebris forest was used as contrast. Pure forest plantations exhibit high and low planting densities, i.e. a spacing of 1.5 m×2 m and 1.5 m×4 m, respectively. Planting spacing in mixed plantations is 1.5 m×2 m. The results were as follows:(1) The Shannon-Wiener index, Simpson''s index, Pielou''s index and richness index of reconstruction plantation types were higher than those of the pure C. funebris forest (1.48, 0.69, 0.82, and 1.27, respectively), except low and high density pure T.sinensis plantation (1.19, 0.65, 0.86, and 0.66, respectively) (1.30, 0.65, 0.72, and 1.15, respectively), low density pure C. septentrionale plantation (1.48, 0.76, 0.92, and 0.85, respectively) and C. septentrionale + A. cremastogyne + T. sinensis plantation (1.44, 0.72, 0.81, and 1.12, respectively). Among all planting patterns, the biological diversity indices of mixed plantations of C. septentrionale + T. sinensis (1.83, 0.83, 0.94, and 1.30, respectively) and A. cremastogyne + T. sinensis (1.82, 0.83, 0.93, and 1.33, respectively) were significantly higher than those of the pure C. funebris forest; the two mixed plantation types were the relatively optimal reconstruction types. (2) The Adiantum capillus-veneris had the widest niche breadth (2.365) before the reconstruction and the ombrophytes were in the dominant position. After the reconstruction, the light condition and soil properties of the undergrowth changed, and heliophytes such as Miscanthus floridulus had rapidly occupied the living space in the low-density pure forest plantations. With increased forest canopy density, ombrophytes such as Carex tristachya, Ficus tikoua, Oplismenus compositus, and Duchesnea indica reoccupied the dominant position. The niche breadth values were significantly positively correlated with the importance values (r=0.916) and resource-niche values (r=0.977). (3) The niche overlap was not related niche breadth, species with wide niche breadths showed both high and low niche overlap values. The niche overlap values between D. indica and Gnaphalium affine were the highest (0.123), but these two species had low niche breadth (0.647 and 2.152, respectively) due to their similar environmental requirements and ecological characteristics. In general, the niche overlap values among the herbaceous communities were low ( < 0.2), which indicates obvious niche differentiation and low interspecific competition. This may be associated with the short reconstruction period.