Weed communities and its dynamics in forest plantations of Sugi(Cryptomeria japonica) at various densities

为研究不同密度下日本柳杉人工林中杂草植被及其动态，在日本东洋半岛南部的东京大学森林中进行了研究。主要调查了不同密度下日本柳杉幼林中杂草植被的种类组成、结构等随年限的变化。同时，研究了人工林木的生长状况和林分结构。在3个处理样地(树密度分别为2,500、3,906、6944株/hm2)的杉木幼林中，禾本科高草型芒杉在2~5年生林分中，各林分种植后均成为优势种。从年变化看，低密度和中密度两个样地中，5年生和5年生后，树高和平均盖度均明显下降，平均树高和平均盖度分别为45%和45%。另一方面，密度最高的林分中，树高和平均盖度在3年生林分和3年生林分成2m后显著减少。因此，在本调查区，当杉木栽植密度为6944株/hm2或以上时，在杉木栽植后的早期、幼龄林分(3年生及以后)，杉木植株有明显减少的趋势。根据这些植被调查结果，可以获得博索南部地区杉木人工林杂草植被动态与树木密度关系的实际情况。

The study was conducted in the forest of Tokyo university in the southern part of the Boso peninsula, to study the weed vegetation and its dynamics in forest plantations of Sugi(Cryptomeria japonica D.DON) at various densities.Species compositions, structure, etc.of weed vegetation changing with years were investigated mainly in a young plantation of Sugi at various densities.At the same time, growth status of planted trees, and forest structure were examined.In a young Sugi-stand with 3 treatment plots(tree density plots of 2,500, 3,906, 6,944 trees per hectare respectively), tall-grass type's Susuki(Miscanthus sinensis ANDERSS) belong to Gramineae has become the most dominant species on 2nd-yr to 5th-yr old stands after planting in each plot.In both plots of the lowest and the middle densities, the coverage percentages of Susuki plants were judged from an annual changes, decreased markedly on and after 5th-yr-old in both plot stands become into 3m, 45% in the mean height and the mean coverage of Sugi planting trees.On the other hand, Susuki plants in the highest density plot decreased markedly in the stands on and after 3rd-yr-old stand become into 2m, 30% in the mean height and the mean coverage of Sugi planting trees.Consequently, in this survey area, when densities of Sugi planting trees were 6,944 trees or over trees per hectare, here showed that Susuki plants have a trend of decreasing markedly in earlier, younger year old stand(on and after 3rd-yr-old stand) after Sugi planting.From results in these vegetation survey, here could to catching an outline of the actual conditions for dynamics of weed vegetation in relations with tree densities in Sugi forest plantations in the southern part of Boso.