大果马蹄荷(Exbucklandia tonkinensis)群落的纬度地带性

大果马蹄荷主产南亚热带至中亚热带南缘,南至海南岛,北至罗霄山脉中段的井冈山、桃源洞地区,是常绿阔叶林的特征种。以纬度地带性(海南霸王岭、广东黑石顶、广东南岭、江西金盆山、江西井冈山、湖南桃源洞)为依托,选定6个具代表性的大果马蹄荷群落开展群落生态学研究,结果表明:(1)各样地物种多样性较高,尤以金盆山蕨类植物9科10属11种、种子植物42科78属128种和桃源洞蕨类植物9科11属12种、种子植物41科79属134种最为丰富。群落组成的优势科主要为金缕梅科、壳斗科、樟科、山茶科、杜鹃花科、山矾科等。(2)从区系特征和环境梯度看,大果马蹄荷群落以南亚热带为分布中心,向南或向北其物种多样性Simpson指数、Shannon-Wiener指数及相应的均匀度指数均呈下降趋势,其中霸王岭、黑石顶、南岭、金盆山、井冈山、桃源洞的Shannon-Wiener指数分别为3.453、4.021、4.130、3.790、3.415、3.712。(3)群落相似性聚类分析显示群落随纬度和随海拔高度形成两个梯度系列,一是以黑石顶、金盆山、井冈山、桃源洞的纬度地带性为一支,相似性系数0.51;二是以南岭和霸王岭聚成海拔梯度较高的另一支,但其相似性系数0.50,为0.33—0.48。(4)大果马蹄荷群落种类组成在区系性质上很相似,具有明显的南亚热带特征;同时,受海拔、地形、气温、降雨条件等因素的影响,种子植物属的热带成分随纬度增加而呈波动性下降趋势。(5)大果马蹄荷种群在各群落中的重要值水平和径级结构表现出一致性,在纬度地带性差异上无明显的相关性。霸王岭大果马蹄荷的径级结构为增长型,但重要值排名为32,说明向南分布该种群优势度明显下降;在南岭、黑石顶、金盆山、桃源洞该种群优势度较大,且为稳定型种群;在井冈山该群落受到人为干忧,大果马蹄荷的重要值排名第1,但为衰退型种群。

Latitudinal zonalization characteristics of the Exbucklandia tonkinensis communities from Hainan Island to the midsection of the Luoxiao Mountains

Exbucklandia tonkinensis primarily distributed from the southern subtropical region as far south as Hainan Island to the southern boundary of the mid-subtropical region, as far north as Jinggangshan and Taoyuandong areas in the midsection of the Luoxiao Mountains is a typical population of the evergreen broad-leaved forest. In accordance with the altitudinal zonalization distribution (Bawangling in Hainan Province, Heishiding in Guangdong Province, Nanling in Guangdong Province, Jinpenshan in Jiangxi Province, Jinggangshan in Jiangxi Province, and Taoyuandong in Hunan Province) and their ecological community characteristics, six representative Exbucklandia tonkinensis communities were investigated. The results indicated as following: (1) High species diversity was showed in all of the six E. tonkinensis communities, especially in Jinpenshan (9 families, 10 genera, and 11 species of ferns, and 42 families, 78 genera, and 128 species of seed plants) and Taoyuandong (9 families, 11 genera, and 12 species of ferns, and 41 families, 79 genera, and 134 species of seed plants). The dominant families of the E. tonkinensis communities were concentrated in Hamamelidaceae, Fagaceae, Lauraceae, Theaceae, Ericaceae, and Symplocaceae. (2) In terms of floristic phytogeography and environmental gradient, the E. Tonkinensis communities were typically centered in the south subtropical zone expressed as the declined values of the Simpson index, Shannon-Wiener index, and Evenness index while extend to the south or north from the centre zone. For instance, the Shannon-Wiener index of Bawangling, Heishiding, Nanling, Jinpenshan, Jinggangshan, and Taoyuandong plots was 3.453, 4.021, 4.130, 3.790, 3.415, and 3.712, respectively. (3) Based on the cluster analysis, the six E. tonkinensis communities are formed into two series along the latitudinal and altitudinal gradient, which the former is Heishiding, Jinpenshan, Jinggangshan, and Taoyuandong, with a similarity coefficient >0.51, and the latter is Nanling and Bawangling, with a similarity coefficient <0.50 (i.e., 0.33-0.48). (4) The species composition of the six E. Tonkinensis communities was very similar in terms of floristic phylogeography, indicating an obvious subtropical property. Furthermore, the tropical component of seed plant genera which was affected by altitude, topography, temperature, rainfall conditions, and other factors was volatility decreased with increasing latitude. And (5) The importance value and size structure of E. tonkinensis populations in each of the six communities are basically, consistent with no significant correlation with differences in latitudinal zonalization. The size structure of the E. tonkinensis population in Bawangling indicating the population was growing, while the importance value of which was 32, indicating that the population dominance decreased southward. The E. tonkinensis population of Nanling, Heishiding, Jinpenshan, and Taoyuandong were predominated and their size structure indicated that the population was stable. Although the importance value of the E. tonkinensis population in Jinggangshan was the highest, the population was declining because of human interference.