洞庭湖湿地柳属木本植物变化趋势及成因

Change Trend of Salix Ligneous Plants in the Dongting Lake Wetlands and Its Reasons

柳属（Salix）植物是洞庭湖湿地唯一的原生木本植物,对湿地生态系统功能的维护具有重要意义,而以往研究大多关注草本植物,缺乏对木本植物的认识。本研究通过2008年5月和2013年11月的洞庭湖湿地大面积调查,揭示洞庭湖湿地柳属木本植物的变化趋势。结果表明,洞庭湖湿地柳属木本植物主要分布于东洞庭湖,其次是南洞庭湖,分布形式为小面积点状分布和大面积带状分布。2008年5月,洞庭湖湿地柳属木本植物分布区的面积为993.7 hm^2,2013年11月减少至192.9 hm^2。2008年5月,洞庭湖湿地柳属木本植物以原生型植物为主,2013年11月,其以种植型植物为主。在2008-2013年间,柳属木本植物呈现分布面积急剧减少、原生型植物减少、种植型植物增加的变化趋势,业已成为本地区的濒危物种。2013年11月,各柳属木本植物分布点的乔木层特征差异明显,树高为4.37-15.2 m,胸径为3.63-68.71 cm,原生型植物树高和胸径明显大于种植型植物。在原生型植物区,林下优势植物主要为短尖薹草（Carex brevicuspis）;在种植型植物区,林下优势植物主要为芦苇（Phragmites australis）、荻（Miscanthus sacchariflorus）和短尖薹草。水位降低、淹水时间缩短、水质下降与大面积种植杨树等是导致洞庭湖湿地柳属木本植物退化的主要原因。

Salix, the only native ligneous plants in the Dongting Lake wetlands, have important role in maintaining the functions of wetland ecosystem. However, these plants were rarely investigated in previous studies. This paper clarified the changed trends of Salix ligneous plants through large-area field investigations in2008 and 2013, respectively. Salix were mainly distributed in the East Dongting Lake and followed by the South Dongting Lake. These plants had 2 distributions types： small-area spotted distribution and large-area zonal distribution. During the period from 2008 to 2013, the area decreased from 993.7 ha to 192.9 ha and main types changed from natural plants to artificial plants. These data indicated that Salix have become the endanger species in the Dongting Lake wetlands. Among all distribution areas, plant height ranged from 4.37 m to 15.2 m and diameter at breast height from 3.63 cm to 68.71 cm. Understory dominant plants were different between natural plants and artificial plants： Carex brevicuspis in the former but Phragmites australis, Miscanthus sacchariflorus, and Carex brevicuspis in the latter. Additionally, decreased water level and water quality, fewer flood time, large-area poplar plantations were the main reasons for degraded trends of Salix in the Dongting Lake wetlands.