| The study area was located in Zhawan Natural Reserve of Anhui Province,in which an old age stand of Castanopsis eyrei was selected for field investigation,the major community formation is Castanopsis eyrei-Rhododendron ovatum+Meliosma veitchiorum-Woodwardia japonica.A sample line method was employed in the paper to account gaps along transects, and then the gap distribution pattern could be estimated and described in the study area. Total 36 gaps in different area have been observed,the results showed that The area of expanded gap(EG) and canopy gap(CG) occupied 27.64%and 7.58%of the total stand area respectively;the major gap shape in the stand was elliptic,the ratio of long axis to short axis for all gaps was about 1.60,and unrelated to gap size.The size of most expanded gaps was less than 200 m~2,the gaps with 100～200m~2 in area were the most in both area and number.And most of canopy gaps was less than 100 m~2,the gaps with 50～100 m~2 in area occupied a higher percentage of total area,but the gaps with area less than 50m~2 were most in number.The uprooting was the most important reason for the gap formation in the studied stands,which represented to 94.44%in number.For the most gaps,gap makers were 1～4 individual,averaging 2.67 individuals of gap makers per gap.The average area of expanded gap and canopy gap formed by a gap maker reached to 72.23 m~2 and 10.80 m~2 respectively.Daily change of light intensity,temperature and other climatic factors in gaps of different size and non-gap stands revealed a unimodel.The peak of the light intensity and the temperature was at 11:00 to 13:00 and 12:00 to 14:00 respectively.Daily change of the humidity of the air was high in the morning and afternoon but low at noon.The minimum of air humidity appeared at 12:30 to 14:30.Throughout the growing period,the light intensity and the temperature performance for different gaps were as follows:big gap＞middle gap＞small gap＞non-gap;and air humidity just the opposite:big gap＜middle gap＜small gap＜non-gap.Gradient change of light in gaps of different size was observed as decreasing gradually from the gap center to understory,and that near to center have the highest reduction range.Daily temperature change at ground surface in different gaps and non-gap location revealed a unimodel,which similar to the daily air temperature change pattern.Its peak appeared at 12:00 to 14:00.The time of the maximum temperature appeared later compared with daily change of light.The average temperature performance was as follows: big gap＞middle gap＞small gap＞non-gap.The soil temperature decreased progressively in the vertical direction with depth increasing.The time of peak temperature appeared postponed with soil depth,and its change amplitude decreased gradually as well.In the other hands,both temperature at ground surface and in soil was lower in earlier and in the end stage of growth period,but higher in the vigorous growth stage.The soil water content displayed in the vertical direction that top layer is higher compared to lower level;In the horizontal direction in gap,author took a big gap as an example,in which soil water content from center to the non-gap stand showed a gradient changing pattern,or the soil water content decreased with distance from gap center to understory.Soil pH was little different between the gap and the non-gap.The pH of soil in the gap was slightly higher than the non-gap for each vertical layer correspondingly.Besides the litter,soil's pH increased gradually with depth,But there are significantly difference for nutrients in vertical layers was found in gap and non-gap.Besides the total potassium content which increased progressively gradually from the litter layer to deeper layer,other nutrient elements were just in reverse,and the nutrient content in litter was higher obviously than other layers.The contents of the organic matter,the total nitrogen,the alkaline hydrolysis nitrogen,the rapidly available phosphorus and the rapidly available potassium in soil in non-gap were higher than those in gap,but the contents of the total phosphorus,the total potassium in soil in gap were higher than those in non-gap.Species composition differences between gap and non-gap could be observed.There were 18 tree species in big gap,then 11 in middle and 13 in small one;for understory species 28 in big gap,21 in both middle and small one respectively.Based on species important value,Alnus trabeculosa was listed at first in both big gap and middle one,but Meliosma veitchiorum and Castanopsis eyrei was at top in small gap;young seedling of Cyclobalanopsis myrsinaefolia and herb species Woodwardia japonica are dominant at undersoty in the 3 different size gaps.This indicated that Cyclobalanopsis myrsinaefolia could grow up into canopy layer and will be dominant species in future.Both of the number of tree species and richness in gaps was higher than that in non-gap,but ecological evenness in gap was lower compared to that in non-gap,Its similar to shrub herb species.Species diversity of tree species was the highest in gaps of 300～400m~2 and the lowest in that of 100～200m~2.SW diversity index and evenness index for different gaps could be list in order as the follows:big gap＞middle gap＞small gap,for ecological dominance:middle gap＞big gap＞small gap.The species richness of the shrub tree and herb species was listed at top in gaps of 300～400m~2,and the smaller gap area is the lower richness could be.The species diversity for both shrub herb species was at top in big gap, and ecological dominance index was the lowest in small gaps,but the highest in middle gaps.The species number,the richness index and the ecological dominance index in the regeneration layer of gaps were the highest in gaps of 300～400m~2.The SW diversity index, the evenness index and the mean degree index reduced along with the gap area increase and was listed at the top in gaps with area less than100m~2.
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