天然次生林中水曲柳种子的扩散格局

 种子扩散是种群动态中的一个关键环节，研究其扩散格局对了解种子库及更新格局有重要意义。于1999～2000年在天然次生林中选择样地并设置样带，共设取样点1376个，观察和估计了水曲柳(Fraxinus mandshurica)的种子雨格局。结果发现，母树附近，尤其是冠幅范围内，各方向的种子雨没有显著差别。但种子雨密度随距离有明显变化，冠幅范围内平均可达462～903个·m-2。距冠缘10～20 m急剧减少，为50～190个·m-2。72.5%～96.4%的种子散落在距母株树干10 m 的范围内。饱满种子顺风

SPATIAL PATTERN OF MANCHURIAN ASH SEED DISPERSAL IN SECONDARY HARDWOOD FORESTS

Seed dispersal plays an important role in subsequent spatial patterns of seed banks and seedlings. The spatial variation of seed dispersal of Manchurian ash (Fraxinus mandshurica), mainly from seed rain, was estimated using geostatistical methods in two plots in secondary hardwood forests in the northeast of China during 1999 and 2000. In plot 1, with only one parent tree of Manchurian ash at the plot center, 8 transects (each of 100 m) radiated away from the sample tree. In plot 2, with an aggregation of parent trees, 4 transects (two 100 m and two 300 m) were radiated away from the biggest sample tree located at the plot center. A total of 1376 sample points were examined in two plots in the various transects. The results showed that there was no obvious difference of seed rain density in any direction, and that rain decreased geometrically with distance from the trunk. 462-903 seeds per m 2 were found beneath the crown, however rain sharply decreased to 50-190 per m 2 at 10 m beyond the crown edge. 72.5%-96.4% of seeds, traveling less than 10 m, landed near the adult. The longest distance of seed dispersal, by wind, was about 70-80 m. The spatial pattern of seed rain showed an approximately clumped tendency near the parent tree, but a random pattern far from it.According to semivariogram analysis, spatial scale of pattern for isotropy in plot 1 was 9.7 m, and the proportion of spatially structured variance was about 60% of the total variance. With the aggregated distribution of parent trees in plot 2, spatial scales of pattern, at 36.6-47.0 m, were about four times stronger than in plot 1. Within these scales, 54.8%-57.7% of the spatial pattern of seed dispersal was spatially autocorrelated. In both plots we also found that animals disturbed the spatial pattern of seed dispersal. Rodents, mainly consumers, predated almost all of Manchurian ash seed (90%-100%) on the forest floor in winter, but there was no clear evidence of predation in other seasons.