水曲柳人工林下天然更新幼苗的空间格局

森林更新受环境梯度影响而形成一定的格局 ,林分水平的更新易受微生境异质性的影响而形成小尺度的空间异质性格局。本研究以东北林业大学哈尔滨实验林场水曲柳 (Fraxinusmandshurica)人工林为研究对象 ,于两个不同密度的林分中设置了不同尺度的 3个样地 ,布设 5 15个格子样方 ,观测水曲柳天然更新幼苗的发生特性 ,测定高生长和样方中幼苗数 ,应用GS +software对调查资料进行了变异函数和分数维分析 ,比较不同密度林分中更新异质性格局的差异 ,并分析了不同更新机制的格局表现。结果表明 ,天然更新幼苗的发生具有明显的空间异质性 ,由空间自相关决定的变异占 70 %以上 ,随机因素引起的变异不到 30 % ,空间自相关尺度为 1 95～ 2 92m。天然更新的幼苗 5月中旬开始出土 ,5月下旬为幼苗发生的高峰期 ,但 9月下旬绝大多数一年生苗死亡。幼苗发生的高峰期 ,更新密度为 16～ 30株 /m2 ;在郁闭度小的林分中天然更新的幼苗较少 ,而在郁闭度较大的林分中天然更新幼苗发生较多 ,格局表现不同于萌芽更新

The Pattern of Natural Regeneration in Plantation of Manchurian Ash

Regeneration is an important ecological process in forest dynamics, which is strongly influenced by environment gradient. The regeneration patterns, in stand level, are often determined by microsite, especially by spatial heterogeneity, which is ubiquitous in forest ecosystem. We hypothesized that natural regeneration pattern of Manchurian ash (%Fraxinus mandshurica%) was heterogeneous, and that there were difference at both different density stand and different regeneration mechanisms. And germination of seedlings was monitored in 515 grid cells set in Manchurian ash plantation, which located in Forest-experiment-station of Northeast Forestry University. To assess heterogeneity scales of seedlings, semivariogram and fractal dimension were calculated by using GS+software. The result indicted that spatial heterogeneity of seeding was obvious, autocorrelated scales were 1 95～2 92 m in isotropy, and over 70% of variance were spatial dependent in study stands. Emergence of seedlings started in middle May, but the timing of peaks was in late May, when the average densities were 16～30 plants/m+2. The heights of first year seedlings were about 7～8 cm. The difference of regeneration patterns were found at different density stands, and response patterns of seedling originated from natural seed rain were different to compare with sprout regeneration which were studied before our research. Our hypothesis was supported by this study.