河谷梯度对湘西北主要河谷特殊生境种子植物区系的影响

Effects of Valley Gradients on the Flora of Seed Plants in the Valley of Northwestern Hu'nan

以湘西北猛洞河("U"型)、德夯("V"型)、小溪︺(""型)3个河谷生境区域为对象,通过比较各河谷生境植物多样性组成、植物区系成分结构,揭示该区域植物区系成分随河谷梯度变化的特征与规律性。结果表明:(1)不同河谷梯度下植物种类组成差异较大,科、属间的相似性系数分别达80%、70%以上,而种的相似性系数仅50%左右。(2)随着河谷梯度的减弱,植物区系热带成分所占比例呈逐步减少趋势,依次为54.56%、46.44%和44.11%;而温带成分却逐步增加,依次为40.00%、50.76%和50.88%。研究发现,3个河谷虽然存在一定的梯度和差异,但它们均是古老成分的避难所和孕育新生成分的摇篮,同时也是湘西北植物的重要分布区域。

In Northwest Hu＇ nan Province, there are kinds of valleys, which are firstly classified into three gradients,i, e. ＂U＂ （e. g. Mengdonghe River Valley） ,＂V＂ （e. g. Dehang Valley） and （e. g. Xiaoxi Valley） ,according to the included angle between slope and base of valley,width of its base and runoff in this paper. Regarding the three valleys mentioned above as our study regions, we compared seed plant diversity composition and flora constituent structure among these different habitat conditions,and then revealed the characteristic and regularity of plant component corresponding to the alteration of gradient of valley. The detailed results are as follows： （1）Species composition shows obvious difference in three gradients of val ley,between which the comparability coefficients get up to more than 80% and 70% at the family and ge nus levels respectively,while only about 50% at species rank. （2）Along with the gradient of valleys weake ning,the portion of tropical component tends to decrease,accounting for 54.56% （Mengdonghe River）, 46.44 （Dehang） and 44.11 （Xiaoxi）. Meanwhile the temperate component is with a trend of ascent of 40.00%,50.76% and 50.88%,respectively. Through this study,we find that all of the three valleys are both a refuge for relict taxa and a cradle for breeding new species ahhough there are certain gradient anddiference among them. Also,they are distinguished areas where seed plants distribute in Northwest Hu＇ nan Province.