林窗对川西周公山柳杉人工林林下物种多样性的影响

采用典型样地法,以川西周公山柳杉人工林5种不同大小的林窗为研究对象,以林下非林窗为对照,研究了不同大小的林窗对柳杉人工林物种多样性的影响,同时分析了不同梯度林窗下林窗中心、林窗边缘、及林下群落的物种组成、物种多样性的变化情况。结果表明:(1)在所调查的18个样地231个样方中共记录到维管束植物141种,隶属于76科113属;随着林窗面积的增大,群落各层次的物种数呈现出先升高后降低的趋势,灌木层物种数在各林窗梯度上表现为林缘林下林窗中心,草本层物种数在各林窗梯度上表现为林缘林窗中心林下。(2)不同林窗优势种及其重要值不同,即在小林窗内,优势种为柳杉和野桐,其重要值之和高达0.292 3;在大林窗内,杉木及亮叶桦为群落优势物种,群落内出现大量其更新幼苗。(3)不同大小的林窗表现为灌木层物种丰富度指数(D)、Shannon-Wienner指数(H)、和Pielou均匀度指数(Jsw)值在400~450 m2面积的大林窗内达到一个均优水平,草本层物种的多样性在面积为100~150m2的小林窗内达到较高水平;不同梯度的林窗各层次群落D、H值整体表现为林缘林窗中心林下。研究认为:林窗的存在会改变群落物种组成,提高群落物种多样性水平,并且大林窗(400~450m2)更利于柳杉人工林林下树种更新及物种多样性的提高。

Effects of Forest Gap on Underforest Species Diversity in a Cryptomeria fortunei Plantation in Zhougong Mountain,West Sichuan

A systematic vegetation survey on the effects of forest gap size on vegetation diversity was conducted in a Cryptomeria fortunei plantation in Zhougong Mountain,Southwest China.Plots were explored in five different sizes of forest gaps,and closed canopy was selected as control.Dynamics of plant community composition and plant diversity in gap centre,gap edge,and closed canopy along the forest gap gradient were investigated.(1)A total of 141 vascular plant species belonging to 76 families and 113 genera were observed across 18 plots including 231 quadrats in this study area.Overall,species diversity shows an increase-decrease pattern with the increase of gap size.The species diversity in shrub layer hierarchically distributes as forest edge>closed canopy>gap centre,while herbaceous species as forest edge>gap centre>closed canopy.(2)The dominant species and important value varies among different sizes of forest gaps.C.fortune and Mallotus japonicus are the dominant species in small size forest gaps,with a sum of important value as high as 0.292 3.While Cunninghamia lanceolata and Betula luminifera are the dominant species in large forest gaps,with plenty of seedlings.(3)Species richness index (D),Shannon-Wienner index (H),and Pielou index (J_sw) reach relative high level in the large forest gaps with sizes of 400-450 m² for shrub communities,while these indexes reach high level in small forest gaps with sizes of 100-150 m² for herbaceous communities.Indexes of D and H among differing communities hierarchically show as forest edge>gap centre>closed canopy.These results suggested that forest gap can influences the composition of plant community and enhances plant diversity,and the large size of forest gap is more beneficial for species regeneration and plant diversity increase.