Diffusion of elm seed rain in Otindag Sand Land
浑善达克沙地沙地榆种子雨的扩散规律

Seed dispersal is an important stage in life style of plant population, the diffusion Pattern of seed directly affect the seedling colonization, distribution and the main resource of propagule. The production of seed is mainly controlled by the seed yield characteristic of tree species, but the seed dispersal not only connected with the tree species, but also with the various environmental disturbance factors. There are difference of seed dispersal pattern among species even, even within population.The characteristic of seed rain directly affect the size, quality, pattern and the reproductive of young seedling. Elm woodland-steppe is spread in the typical temperate steppe zone. Sand elm is the top community which adapt well to the semiarid and sub-humid sandy. Sand elm in Otindag Sand Land can protect the local environment effectively. But with the decrease of population of Sand elm recently, the stability and sustainable development will be hindered. Therefore, there has an imperative require for the population renewal strategies and vegetation restoration when considering the seed rain spatial and temporal distribution features. Through observing the seed rain's quantity, composition and dissemination process for different age isolation elm wood in Otindag Sand Land, we try to illuminate the diffusion rule of seed rain and the relationship between the diffusion of seed rain and the external environment by continuous observation in original position. By selected the different ages of sand elm wood (23 years, 40 years and 56 years) located in Otindag Sandy Land, the seed rain's quantity, composition, distribution process and the relationship between the disperse rule of seed rain and the environmental factors. The study area is located in the middle of Otindag Sandy Land in Sang Genda town attached to Zhenglan Banner(N42°41'-43°43',E115°57'-115°59'). The experiment was conduced continuously from 18th May to the end of 2th July 2010. We selected three kind of wood isolated with different ages (23 years, 40 years, 56 years) which in the uniform habitat such as elevation, slope, aspect and other conditions. At the same time, no sand elm was found around 100 m in the upper direction and around 50 m in the other three direction of isolated wood. The Seed rain collector was laid as the local main direction, surrounded with the isolate wood and separated for 5 meters from one collector to another. 120 collectors were distributed in 10 sub-direction. The Seed rain was collected every 2 day from the seed rain began to drop, until the seed falling completed. The collected sand elm seeds (with Samara) were divided into 5 levels according the intact and mature degree of seed. The level 1 of seed means the intact Samara and mature seeds, the level 2 means the winged Samara and the incomplete mature seeds, the level 3 means mature seed without Samar, the level 4 means seeds rotted or destroyed by insects and the level 5 means immature or empty seeds. One way A