天然林重建过程中单优箬叶竹灌丛对树木更新的影响

利用1996年在湖南省会同林区布置的20个1 hm~2的实验样地,以剔除或林下不含箬叶竹样地作为对照(C),保留箬叶竹作为处理(I),评估了天然林重建过程中林下单优箬叶竹灌丛形成对树种更新过程的影响.处理10a以后结果显示,箬叶竹灌丛盖度上升到95%.进一步通过2007年两种样地乔木多度、多样性、生物量以及物种组成等指标的测量表明,单优箬叶竹灌丛显著抑制了树种的存活与生长,18～390 cm高度级别的树种多度和多样性显著降低,尽管高度18 cm以下级别的幼苗以及成年树的多度和多样性没有显著下降,但是生物量从幼苗到成年树,处理样地普遍下降.幼苗、幼树、成年树地上部分生物量分别下降47.45%、39.87%、59.64%,地下部分生物量分别下降55.70%、46.08%、63.62%.NMS(非计量多元尺度法)排序进一步表明两种样地具有显著不同的树种组成,揭示两种样地处于不同的演替更新阶段.结果表明单优箬叶竹灌丛的形成能延缓树种更新的进程,因此天然林重建过程中应注意避免该类林下植被的出现.

Effect of monodominant long-auricled indocalamus (Indocalamus longiauritus) thickets on tree regeneration during reestablishment of natural forest

We evaluated the influence of long-auricled indocalamus (Indocalamus longiauritus Hand.-Mazz.) monodominant thickets in understory layers of tree regenerations during the reestablishment process of natural forests. A manipulative field experiment was performed in pure Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations in Huitong, Hunan Province, located in the subtropical part of China. Ten 1hm~2 permanent plots with long-auricled indocalamus in understory (I) were selected as treatment and another ten 1hm~2 permanent plots (C) were used as control plots in which there is no any bamboo. In 1996, all canopy Chinese fir individuals were removed to improve understory light condition and to promote the establishment of monodominant thickets in these plots. After 10 years, dense bamboo layers with about 95% cover were successfully established. In 2007, we measured the abundance, diversity and biomass of tree seedling, sapling and adult tree by height class in all treatment and control plots. The formation of long-auricled indocalamus monodominant thickets significantly impeded the tree survival and growth. The abundance and diversity of saplings in the 18-390 cm height classes were lower in the treatment plots. Although the dense bamboo layers did not significantly reduce the abundance and diversity of tree seedlings of less than 18 cm height and canopy trees, the biomass of seedlings, saplings and canopy trees decreased by 47.45%, 39.87% and 59.64% for the aboveground portion and by 55.70%, 46.08% and 63.62% for the belowground portion, respectively. Non-metric multidimensional scaling (NMS) ordination showed different patterns in species compositions between treatment and control plots, which further indicated that tree regeneration in these two types of plots was not in the same succession phase. Our results support the hypothesis that the formation of dense bamboo thickets would slow the tree regeneration process. Our study suggests that the formation of monodominant understory layers during reestablishment of natural forest should be avoided.