瓦屋山中亚热带湿性常绿阔叶林的林窗形成特征

Gap formation features of humid evergreen broad-leaved forest in central subtropical Wawushan Mountain,Sichuan Province,China.

调查了瓦屋山原生和次生的中亚热带湿性常绿阔叶林的林窗形成特征 ,并对林窗形成特征、林窗制造者的死亡方式和原因进行了探讨 .结果表明 ,次生常绿阔叶林林窗面积均 <10m2 ,1hm2 仅 9个 ,林下更新不明显 .原生林林窗密度为 1hm2 15个 ,<40m2 的林窗占 5 6% ,>10 0m2 的林窗只有 4个 ;林窗平均面积 5 9m2 ,扩展林窗平均面积 10 5m2 ,林窗和扩展林窗总面积占被调查林分的比例分别为 11 1%和 19 8% ;林窗大小分布表现出负指数分布 ,即小林窗多、大林窗少 ;林窗形状的变异较大 ,大多数因边界木的多少而成不规则的多边形 ;大多数林窗是多个林木死亡事件的结果 ,因而大多数林窗有两个或两个以上的林窗制造者 ;各林窗年龄大多数在10a以上 ,最近形成的林窗极少 ,估计林窗形成率是 0 0 1·a-1;采用样地投影调查方法可提高测定精度 ,便于不同调查林分结果的有效比较 .常绿阔叶林林窗形成原因较为复杂 ,小径木的死亡是竞争被压所致 ,而大径的较高冠层木的死亡则可能是树木生长发育以及与地形、风等自然因子相互作用的结果 .

The primary and secondary subtropical evergreen broad-leaved forests at an altitude of 1720～1750m in Mt. Wawushan National Forest Park, southwestern China investigated to analyze their canopy gap formation characteristics.The sampling method and canopy formation causes were also discussed.In secondary evergreen broad-leaved fore- st,the gap density was surprisingly only 9 per hm 2 and the size of all gaps was,no more than 10m 2. Almost every gap had only one gap maker,and the gap makers often died standing by suppression. Accordingly successful natural regeneration is difficult in small gap,due to the rapidly lateral growth of canopy trees. In primary evergreen broad-leaved forest, the gap density was 15 per hm 2, and 56% of the gaps had an area of no more than 40m 2. The largest gap had an area of 256m 2. The canopy gap accounted for 11.1% and expended gap occupied 19 8% of land area in the forest. Median area of canopy gaps and expended gaps was 59 and 105m 2, respectively. Most gaps had more than one gap maker,and gap makers died falling and were often from mortality events separated in time. Most gaps aged over 10yr and a few were formed recently and the estimated gap formation rate was 0 01 per year. According to falling direction of trees and the relations with growth process, slope aspect and wind, we deduced gap-maker death resulted from integrated influence among topography,climate particular in wind, tree growth characteristics, and interactions of population under competition. Adapting method of plot sampling and projection drawing used in the paper can improve investigation accuracy and help improving comparison of results in different investigation area.