草地沙化过程地上植被与土壤种子库变化特征

研究了草地沙漠化过程地上植被与土壤种子库的变化特征,获如下结论:(1)草地沙漠化过程地上植被与土壤种子库物种多样性的衰减模式不同,土壤种子库植物种数从潜在沙漠化阶段(固定沙地)到中度沙漠化阶段(半流动沙地)变化很小,而从中度沙漠化到严重沙漠化阶段(流动沙地)衰减速度明显加快;地上植被种数随着沙漠化程度增加而下降,其中从中度沙漠化到严重沙漠化发展阶段衰减幅度最大。(2)地上植被与土壤种子库密度随着沙漠化程度增加而下降,但下降速率因沙漠化发展阶段不同而异,从固定到半固定沙地是地上植被与土壤种子库密度下降最快的时期。(3)地上植被与土壤种子库共有种数随着沙漠化程度的增加而减少,从而导致了地上与土壤种子库群落组成的相异性增大。(4)4种退化沙地土壤种子库组成的相似性要高于地上植被,表明在沙漠化过程中土壤种子库群落组成的稳定性要高于地上植被。(5)地上植被密度与土壤种子库密度存在显著相关性,其关系可用二次曲线来描述。

封育对退化沙质草地土壤种子库与地上群落结构的影响

对封育和未封育放牧草地土壤种子库、地上幼苗库和定植群落的结构特征进行了比较研究,并探讨了地上植被与土壤种子库密度的关系,主要结论是:1)对退化沙地实施封育措施后显著提高了地上植被与土壤种子库的密度和植物种数,特别是显著增加了地上与土壤种子库群落中优良禾草的种数与密度,草地质量得到很大改善。2)地上植被与土壤种子库对放牧干扰的响应模式不同,放牧对地上植被种丰富度的影响要明显大于土壤种子库,而对土壤种子库密度的影响又明显大于地上植被。3)由于放牧显著降低了地上植被与土壤种子库的共有种数,从而降低了地上植被与土壤种子库组成上的相似性。另外,封育和未封育草地在种子库组成上的相似性要高于地上植被组成上的相似性,提供了放牧更强烈地影响地上植被组成的重要佐证。4)回归分析显示,土壤种子库密度与地上早期幼苗库密度和后期定植群落密度以及幼苗库密度与定植群落密度之间均存在显著的正相关性,早期幼苗库密度的56%的变异可归结为土壤种子库密度的变异,而后期定植群落密度的77%的变异可由早期幼苗库密度的变异来解释。

乳源木莲杉木混交林生长及其竞争关系分析

Fixed sample plots were set up for researching competition relationships between Manglietia yuyuanensis and Cunninghamia lanceolata in 17-year-old M.yuyuanensis stands mixed wiht C.lanceolata. The interspecific competition intensity in different mixed stands was determined by using the competition indexes constructed with diameter of breast height, the volume of tree crown and distance between trees, through Hegyi’s Competition Index Model. The results showed that the spatial distribution of M. yuyuanensis in mixed stands was stochastic, the numbers of M. yuyuanensis and C. lanceolata around each M. yuyuanensis increased with the increase of the distance. Under the steady density, the ratios of C.lanceolata to M. yuyuanensis directly affect the interspecific competition and the growth. When the ratios of C.lanceolata to M. yuyuanensis were in the scope of 9-1 to 7-3, M. yuyuanensis had the obvious increase production trend compared with its pure stand. When the ratio was 9-1, the tree height and the diameter of breast height of M. yuyuanensis increase by 22.3% and 69.3% respectively; likewise, when the ratio was 8-2, they increase by 23.2% and 56.9% respectively, because at this ratio, the number of M. yuyuanensis in mixed stand was so low that its competition was mainly the interspecific competition from C.lanceolata. The competition index of M. yuyuanensis was 1.67 times lower than that in pure stand, especially the competition index constructed by the tree-crown volume was 21 times lower. however, when the ratios were in the scope of 6-4 to 5-5, M. yuyuanensis obviouly decreased production compared with pure stand, the intraspecific competition of M. yuyuanensis becomes stronger when its number increased. Based on the mechanism of stemwood cultivation, initial planting density of M. yuyuanensis trees should be reduced properly and higher ratio of C.lanceolata to M. yuyuanensis should be 8-2 or small higher in order to realize the cultivation goal of large timber of M. yuyuanensis .

基于Moran′s I的林分空间结构量化指标自相关分析

为了研究林分空间单元中对象木与相邻木之间在空间结构指标上的自相关性,分析对象林木与相邻木之间在空间中的逻辑关系。在大围山自然保护区、乌云界自然保护区及芦头林场等区域中设置了25块20m×20m的样地,构建了基于Voronoi图的林木空间单元,确定了每株对象林木的相邻木,并选取混交度、开阔比数、胸径大小比及竞争指数作为林木空间结构量化指标,计算了各指标的值,最后结合全局Moran′s I的基本原理构建了林分空间结构单元指标自相关性分析方案,对研究样地中的林分进行分析。结果表明,研究区域的林分为中度混交混交林,该区域的林木之间处于呈中拥挤状态,研究区域内的对象木和其空间单元内的相邻木胸径大小分布差异性较大,林木之间的竞争相对较强。从空间关系上看,研究区域内林木的混交度、开阔比数与其相邻木在空间上呈正相关,在逻辑上表现为聚集;林木的胸径大小比、竞争指数与其相邻木在空间上呈负相关,在逻辑上表现为离散。此外,调研区域中的林木在空间上与其相邻木的关系主要表现为竞争,林分中林木的混交度和竞争指数可能是导致其与周围相邻木存在负相关的主要空间指标。