两个林分水曲柳土壤种子库空间格局的定量比较

依据地统计理论和方法，采取规则网格数据结构的空间取样设计，在树种组成、林分密度及林下植被等均不相同的两个林分中设置样地，对水曲柳土壤种子库的空间格局进行了定量比较研究．结果表明，在水曲柳杨树等混生的样地1，种子库密度较大(158．1±96．7个·m^-2)，异质性程度较高(C0+C＝0．549)，格局尺度相对较大(4．52m)，空间自相关因素引起的变异高达89．4％，随机变异仅占10．6％，格局变异呈现较高的自相似性(分数维值D＝1．728—1．865)．在水曲柳纯林中的样地2，种子库密度较小(57．4±44．7个·m^-2)，异质性程度较低(C0+C＝0．125)，且主要体现在相对较小的尺度范围内(2．59m)，空间自相关变异占56．8％，随机因素对空间格局的影响较大(D＝1．906—1．960)．两样地之间种子库空间格局表现的尺度范围、强度及空间结构等有显著差异，林分空间异质性是导致这种差异的主要原因．

Quantification comparison of spatial pattern of soil seed bank of Fraxinus mandshurica in two stands

The spatial pattern of soil seed bank of Fraxinus mandshurica were examined by geostatistics in two stands with different densities, tree species composition and ground plants, in the Northeast of China. A sampling grid of 559 points, at each point a sample was located, was established according to regular grid design at three spatial scales (cell size were 0.5 m x 0.5 m, 1 m x 1 m, and 2 m x 2 m) in each plot. Spatial pattern were quantified by using semivariance analysis, fractal dimension and Kriging maps. The object of this paper is to quantify the spatial pattern of seed bank, to compare its variations between two stands, and to explore what sort of mechanism would control its variations. The results indicated seed distribution showed appreciable heterogeneity within stand and clearly difference between the two stands. In plot 1 (mixed stand), seed bank, with a mean of 158.1 +/- 96.7 seeds.m-2, higher sill (C0 + C = 0.549) and 4.25 m scales, has a stronger spatial pattern. There were a high autocorrelated variation (89.4%) and lowly random variation (10.6%) at this scale. However, at scale from 5 m to 31.3 m, its autocorrelated variation ranged 51.4%-69.8% and random variation ranged 30.2%-47.6%, also has distinctly mosaic patterns. Fractal dimension (D) analysis showed that the D values was relatively lower(1.728-1.865), their coefficient of variation only about 26.7%-68.35%, indicated that there was a high self-similarity of patch shapes of seed bank. In plot 2 (pure stand), with a mean of 57.4 +/- 44.7 seed.m-2, and lower sill (C0 + C = 0.125), spatial patterns were not so strong as plot 1, which has a smaller scale (2.59 m). Its spatially autocorrelated variation was 56.8% and randomly variation was 43.2%. Over the scale there were no clearly autocorrelated spatial patterns. Fractal dimension analysis showed higher D value (1.906-1.960), and their coefficient of variation varying wildly (69.51%-134.14%), implying highly random variation and more complex patch shapes. The differences of spatial pattern of seed bank between the two stands were likely to be due to spatial heterogeneity at the level of stands.