中文摘要：

以一片西南桦（Betula alnoides）天然林和一个西南桦独立单株为研究对象,通过收集散种期内与林分或母树不同距离的种子以及测定风速和风向,研究了西南桦群落和个体水平上种子雨的时空动态及其与风速和风向的关系。结果表明：群落水平上,西南桦种子散布的初始期、高峰期、消退期分别历时11天、32天和40天,而个体水平上则为9天、25天和26天。高峰期内群落和个体水平的散种量分别占其总量的83.1%和68.7%,而且白天的种子雨密度高于夜间;西南桦个体白天种子雨密度最大的时段为12：00–16：00,与此时段内风速较高有关。在个体水平上,距离母树0–30m范围内散落的种子占总散种量的79.6%;而在群落水平上,距离林缘0–45m范围内集中了总散种量的81.2%。西南桦种子散布具有方向性,无论个体还是群落水平上不同方向间种子雨密度差异极显著（p〈0.01）,与散种期内的主要风向有关;而且种子雨密度与风速亦呈极显著正相关关系。研究结果将有助于揭示西南桦天然更新动态和更新机制,亦为开展西南桦人工促进天然更新提供理论依据。

英文摘要：

Aims Our objective was to study spatiotemporal dynamics of seed dispersal of Betula alnoides and analyze its correlation with wind speed and wind direction at community and individual levels. Methods Seed dispersal was investigated for a natural forest and an isolated tree of B. alnoides. We set seven sample lines 100 to 355 m long in or around the natural forest. One seed trap was placed every 5 m, and seeds were collected every two days. We set eight sample lines （east, southeast, south, southwest, west, northwest, north, northeast） around the isolated tree. Three seed traps were placed every 5 m from 0 to 50 m and every 10 m from 60 to 150 m, and seeds were collected each day. Wind speed and wind directions were measured at two sites. Seed rain density was calculated. Important findings The seed rain lasted 83 and 60 days at the community and individual levels, respectively. The starting, fastigium and subsiding stages of seed dispersal lasted 11, 32 and 40 days for the community and 9, 25 and 26 days for the isolated individual. Seeds dispersed at the fastigium stage accounted for 83.1% and 68.7% of all seeds collected at the community and individual levels, respectively. Seed rain density was higher during the day than at night, and the highest seed rain density by day occurred at 12：00-16：00. At the individual level, seed rain density decreased with increasing distance from the maternal tree, and 79.6% of seeds were collected in the area of 0-30 m around the maternal tree. Seed rain density at the community level also decreased with longer dis- tance from the forest edge, and 79.6% of seeds were collected in the area of 0-45 m around the forest edge. The seed rain density was significantly different among directions （p 〈 0.01）, which was affected by wind direction. Seed rain density was also positively affected by wind speed （p 〈 0.05）.