清除优势草本植物对西双版纳飞机草-马唐群落中木本幼苗的影响

在农业弃耕地上通常会出现由草本植物占优势的演替早期群落。为研究优势草本植物对群落中木本幼苗及群落微环境的影响以及外来入侵植物和本地植物对木本幼苗的影响有何差异,在西双版纳地区选取由外来入侵植物飞机草和本地植物马唐共同占优势的演替早期群落,实施物种清除实验,观测样地中木本幼苗的高增长及死亡补充情况,同时对群落微环境进行观测。结果显示,清除优势种显著提高了木本幼苗的高增长,降低了其死亡率,并且使新增幼苗数量有所提高。清除优势种对0-50cm幼苗高增长和死亡率的影响均大于50-100(或200)cm幼苗。清除处理显著提高了样地的冠层下可见天空比例,但对土壤含水量和土壤养分的影响并不显著。飞机草和马唐均能形成浓密的冠层,通过对光的竞争抑制木本幼苗的生长,且这两者的抑制作用没有显著差异。该地区次生林中常见的先锋树种在研究样地内均有幼苗存在,但其生长却受到优势草本植物的强烈抑制。因此,对演替早期群落中草本植物的控制与管理应同时注意外来入侵物种与本地杂草。

The effects of removing dominant herbaceous species on woody seedling growth in Chromolaena odorata + Digitaria ciliaris community in Xishuangbanna,

Early successional communities in abandoned agricultural fields are often dominated by herbaceous species. To study the effects of dominant herbaceous species on woody seedlings and microenvironmental factors, and to contrast these effects between invasive species and native species, we conducted a species\|removal experiment in an early successional community dominated by invasive species (Chromolaena odorata) and native species (Digitaria ciliaris) in Xishuangbanna, southwest China. After the removal treatment, we investigated the recruitment, growth and mortality of woody seedlings. We also measured microenvironmental factors in the community. We found that the seedling height increment was substantially greater in removal plots than in control plots, the mortality of woody seedlings decreased, and the number of new seedlings increased after removal treatments. The effect of removing dominant species on height increment and seedling mortality was larger on 0-50 cm seedlings than on seedlings taller than 50 cm. The removal treatments increased the diffuse non\|interceptance value (DIFN) significantly but had little effects on soil moisture or soil nutrient status. Both the invasive species and the native species formed dense canopies and inhibited the growth of woody seedlings by competing for light, with no significant difference between these two species. The seedlings of pioneer tree species were found in the study area but they were subjected to severe inhibition by dominant herbaceous species; both the invasive and the native weed species. Therefore, attention should be paid to both invasive species and native weeds in managing dominant herbaceous species in early successional communities.