不同强度火干扰下盘古林场天然落叶松林的空间结构

基于2011年7月大兴安岭外业调查数据以林隙为主要研究对象,选取景观生态学中斑块类型指数分析样地内林隙状况,并结合林木分布状态,分析不同强度林火干扰对天然落叶松林空间结构的影响。结果表明:在受中度林火干扰的林分内,只保留了少量的落叶松中径木、大径木,先锋树种在林分内呈现聚集分布;在未受林火干扰的林分和受林火轻微干扰的林分内,天然落叶松均呈现显著聚集分布;由于受到不同强度的林火干扰,林下区域与林隙区域出现不同程度的相互转化,林分空间结构发生了改变。林分按照所受林火干扰强度的递减,在同一时间不同空间上表现出了森林循环过程中所经历的林隙阶段状态、建立阶段状态、成熟阶段状态。

A dynamic analysis of spatial distribution pattern of Larix gmelinii natural forest in Pangu farm under varying intensity of fire disturbance

Fire is the most common disturbance in natural forested ecosystems and plays a significant role in ecological succession of forest communities. Fires often burn in the Da Hinggan Mountains (also known as the Greater Khingan Mountains) where frequent high-intensity fires rapidly transform the landscape. These fires have extensive and long term effects on the spatial distribution of natural Larix gmelinii forest. This study looks mainly at gaps formed by fires of different severity in natural L. gmelinii forest and is based on data from records collected at the Pangu Farm, Tahe Forest Bureau, Da Hinggan Mountains in July 2011. We describe the dynamic processes which create tree spatial distribution patterns of natural L. gmelinii forest in Pangu farm. Our research looked at how fires of varying severity influenced the spatial distribution patterns of natural L. gmelinii forests by analyzing gaps in plots. We selected suitable class parameters at a landscape scale and combined with the state of tree spatial distribution patterns. We defined three phases, the gaps phase, immature phase and mature phase. The results show stands which suffered moderate fire disturbance are moved into the gaps phase of the forest cycle; these stands retain only a small amount of medium and large diameter live trees of L. gmelinii. Pioneer species reveal aggregative distribution in the newly created patchwork of gaps of different sizes; the distance between the patches was the shortest of the three phases and the shapes of the patches themselves are very complicated since moderately intense fire leaves a significant and irregular accumulation of gaps within any particular plot. The research plot, in a stand that was burned with low intensity fire, retained most of its L. gmelinii, and continued to develop along the normal lines of forest succession. Low intensity fire allowed L. gmelinii to continue to maintain its aggregative distribution. A large number of pioneer species invaded into the area burned with low intensity fire. The low intensity burn area had the smallest gap patches of the three phases studied. The shape of these small gap patches was the most uniform and the separation between the gap patches was the largest of the three phases. The unburned plot with no known history of fire disturbance was a mature phase forest and included a complex patchwork or network of gaps of different sizes. The unburned L. gmelinii community had changed from an aggregative distribution into a uniform distribution. Because fires burn with different levels of intensity, the undergrowth was transformed into gap patches. The spatial distribution pattern had changed with fire distribution. As the level of fire disturbance declined in a particular stand the area moved from the gaps phase, to the immature phase and then the mature phase in the forest cycle.