恩施天然红椿种群结构及空间分布格局

红椿Toona ciliata是国家Ⅱ级重点保护野生植物，以红椿为优势种的天然种群十分少见。对湖北省恩施州4个不同红椿天然种群设立样方调查。编制了红椿特定时间生命表，绘制存活曲线，对种群龄级数量进行动态预测，并对空间分布格局进行分析，以研究不同种群空间结构和分布格局的成因。结果显示:4个种群的人为干扰强度:T4＞T1＞T2＞T3；4个种群结构动态指数Vpi分别为23.8%, 34.0%, 27.8%和 32.3%，均为增长型。由于不同外界干扰强度，不同种群死亡率（qx）出现在龄级上推迟的现象；最高进入x龄级个体的生命期望（ex）值T3＞T4＞T1＞T2。存活曲线不符合Deevey曲线，模拟符合三次函数曲线。25，50和100 m2取样面积上，方差／均值比率法的t检验、Morisita指数I参数的F检验、负二项参数K值均表明:T1和T4种群为聚集分布，T2和T3种群为泊松分布。聚集强度T4＞T1＞T2＞T3；拥挤程度:T1＞T4＞T3＞T2。研究表明:红椿种群在自然状态下处于增长状态，潜在干扰影响时，仍表现为稳定种群。红椿天然种群以泊松分布为特征，聚集分布主要来源于人为干扰。适当人为干扰，可以促进红椿种群更新、物种保护和生态效益最大化。图2表5参25

Spatial structure and distribution pattern of natural Toona ciliata populations in the Enshi Region

Toona ciliata is a key protected tree species at the second national level, its natural population acts as a dominant species in its existing community, is rarely seen in subtropical regions of China. This study was to research the structure of age class, the quantity dynamic conditions, the trend of development and the correlation between the distribution pattern and the structure of age class, the quantity dynamic condition of different Toona ciliata populations. Four sample plots were selected in the Enshi Region of Hubei. The sample plots, entirely covering 4 populations, were set up, each in 5 m 5 m grid, by using contiguous grid quadrate method, with T1 10 m 30 m, T2 20 m 20 m, T3 20 m 20 m and T4 10 m 40 m in size respectively. Based on field survey data, a specific life table was established, survival curve was determined, a dynamic estimation of the survival number for different age classes was made, and spatial distribution patterns of different Toona ciliata populations were analyzed to determine the causes of spatial structures and distribution patterns in different sampling plots. Analysis included Deevey curves, regression, ratio method of variance mean value with t test, Morisita indices （I） with F test and negative binomial parameter （K）, patchiness index （m*/m）, and mean crowding index （m*）. Results of the human disturbance intensity for the four populations was T4 ＞ T1 ＞ T2 ＞ T3 with dynamic indices （Vpi） of T1 = 23.8%, T2 = 34.1%, T3 = 27.8%, and T4 = 32.3% showing growth form. Also, the qx values of different populations lagged in age-class with external disturbance intensities, and the life expectancy peak values （ex） varied as follows: T3 ＞ T4 ＞ T1 ＞ T2. Survival curves did not agree with any Deevey curves, but 4 cubic functions represented a regression of the four survival curves: y=－0.121S3 +2.469S2－14.814S+31.071, y=－0.136S3 +2.162S2 －11.297S + 23.286, y=－0.287S3 +4.410S2 －19.992S +31.143, y=－0.058S3 +1.492S2－10.64S + 24.357; With 25 m2, 50 m2, and 100 m2 as sample sizes, a ratio of variance and mean value to t test, I with F test, and K all demonstrated that T1 and T4 populations had clumped distributions, but T2 and T3 had Poisson distributions. The m*/m varied with a sequence of T4 ＞ T1 ＞ T2 ＞ T3; whereas, m* was T1 ＞ T4 ＞ T3 ＞ T2. This research demonstrated that in a natural state, the Toona ciliata population was in growth form with a stable population susceptible to potential external disturbances and having a Poisson distribution, but with human disturbance a clumped distribution emerged that with proper human objective regulations, population regeneration, species protection, and maximum ecological effect could be enhanced.［Ch, 2 fig. 5 tab. 25 ref.］