濒危植物凹叶厚朴幼苗更新及环境解释

Characteristics and Environmental Interpretation of Seedling Regeneration in the Endangered Species Magnolia officinalis subsp.biloba

凹叶厚朴为我国二级保护野生植物,由于其较高的药用价值,野生资源遭到无节制的盗砍,造成种群数的衰退和群落残败。调查浙江省遂昌县桂洋林场不同群落野生凹叶厚朴的更新状况,结果表明:凹叶厚朴种群大小级为不典型的"J"型,种群在较长的时间内保持稳定状态;凹叶厚朴以萌生更新为主,随着群落郁闭度的增加,萌生苗的比例增高,但不同群落平均萌枝数量、平均胸径及株高无显著差异。实生苗随着郁闭度的增加植株呈现变矮、变细的趋势;凹叶厚朴实生和萌生苗在不同群落中年龄结构差异均极大,针阔叶混交林中更新良好,针叶林大量高龄幼苗生长缓慢,且植株不易进入上层空间,常绿阔叶林中存在严重的更新不良现象;各群落中,更新幼苗株高和胸径增长量均随郁闭度的增加呈现极显著下降的趋势,其中实生苗的下降趋势更为明显;影响实生更新的主要环境因子为草本层盖度和厚度、枯落物盖度、腐殖质厚度及土壤含水率;影响种群萌生更新的主要环境因子为群落的光照及温湿度。因此,降低上层林冠密度,减少草本层、枯落物等的覆盖对于维持种群的发展、缓解其濒危状况具有重要的意义。

Magnolia officinalis subsp, biloba is an endangered plant species that has been categorized as one of the second grade state protection wild plants of China. The overexploitation of this species due to its high medicinal value has resulted in resource reduction, population declining, and community recession. This research was undertaken to explore the regeneration characteristics of M. officinalis subsp, biloba and the factors that may limit the process. A field survey of the species was undertaken and the age structure, seedling characteristics, and obstacles to regeneration were identified. The frequency distribution of sizes of M. officinalis subsp, biloba individuals was found to be a typical J-type, suggesting that the population would maintain stability over a relatively long time. Sprouts occupied a large proportion of three communities studied and the proportion increased as the canopy density increased. The sprouts showed no significant difference in average branch number, height, and diameter at breast height （DBH） over various densities while the seedlings decreased in height and DBH as the canopy density increased. The age structure of seedlings and sprouts displayed great variability in different communities. Seedling regeneration was common under the coniferous and broad- leaved mixed forest. Regeneration of this species under various forest canopy varies in the order of broad-leaved forest 〈 coniferous forest 〈 mixed forest due to the increase in canopy density. Increments of DBH and height of the sprouts and seedlings decreased significantly with an increase of canopy density, with seedlings decreasing more rapidly than sprouts. The main environmental limiting factors that control seedling regeneration were herb cover and thickness, litter cover, humus thickness, and soil moisture content. For sprout regeneration, the main limiting factors were light intensity, temperature, and moisture of the community. The results suggest that decreases in the canopy density and the herb and litter coverage are effective means to promote the regeneration.