洞庭湖森林生态系统空间结构均质性评价

以东、南、西洞庭湖区域君山岛、龙山、赤山岛龙虎山林场、明朗山、常德林场、和洑林场和桃源县天然次生林为对象,借鉴生态学有关生态系统内部均衡和均质原理,在森林生态系统(斑块)尺度,从空间结构的混交、竞争、空间分布格局3个方面分析提出空间优化的均质性目标、均质性指数及均质性评价方法和评价标准.结果表明:15个洞庭湖湿地调查林分平均均质性评价指数为0.2517.均质性评价的5个等级中处于l级和2级的林分为12个,占80％,处于3级的林分只有3个,仅占20％.说明洞庭湖各林分整体上在空间结构、生长环境和树种优势度等方面不具有明显优势,离理想空间结构差距太大；按照高程不同,洞庭湖湿地从湖沼到丘陵岗地,林分空间结构均质性特征逐渐增强.森林生态系统空间优化均质性目标及均质性指数的提出是森林可持续经营空间途径的拓展,为森林经营的理想空间结构及其表达探索一条新途径.

Heterogeneity evaluation of forest ecological system spatial structure in Dongting Lake

The spatial structure rationality evaluation and ideal spatial structure of forest ecosystem is an important and difficult problem in forest management at home and abroad. In order to reveal the reasons why the community structure is simple and the stability of ecosystem is poor, and to take the regulation mechanism of structure in Dongting Lake forest, the research is targeted at East, South, West Dongting Lake area including Junshan Island, Longshan, Longhu forest farm on Chishan Island, Minglang mountain, Changde forest farm, Hefu Forest farm and natural secondary forest of Taoyuan County. Utilizing the ecosystem internal balance and homogenizing principle of the ecology, in the forest ecological system (plaque) scale, it analyses the spatial structure of mixed, competed and spatial distribution pattern. And then the heterogeneity goal of optimized stand spatial structure is proposed, which has multiple sub-goals in mixed, competed and spatial distribution pattern. Meanwhile the heterogeneity index of single tree and stand spatial structure is also defined, and the evaluation index, evaluation method and evaluation standard of stand spatial structure heterogeneity is determined. By applying the proposed evaluation method to the Dongting Lake area secondary forest heterogeneity evaluation, the results show that: in the fifteen Dongting Lake wetlands under investigation, the forest stand average homogeneity evaluation index is 0.2517. There are 12 stands in the grade 1 and grade 2 which is accounted for 80%, and only 3 stands in the 3 grade accounted for only 20% in the five grades of homogeneity index. However, it lacks of the grade 4 and grade 5 ideal stand spatial structure in Dongting Lake survey. The evaluation results show that only part of stand spatial structure factors in Dongting Lake Forest meet the standard values. Although there is a certain degree of mixed size between dominant tree species and pioneer species, and there are more obvious differentiation between even-aged and uneven-aged forest stands, it yet shows that: the whole stand appears monolayer, and tree species has little isolation; trees' distribution pattern appears randomized into uniform distribution status; competition is more obvious between individual trees, and it has low diversity and weak illumination. It illustrates that the Dongting Lake stands as a whole have unconspicuous advantage on spatial structure, growth environment and species dominance and other aspects. Many irrational factors exist in forest structural characteristics including space information, and there is far from ideal spatial structure. According to the different altitudes, forest spatial structure homogeneity characteristics gradually grow from the lake to the hilly land in Dongting Lake wetland. This conclusion reflects the real situation of forest resources in Dongting Lake area, and it has a close relationship with the long-term natural and man-made interference, protection and restoration of fatigue.The proposed forest ecological system space optimization objectives and heterogeneity index prolongate the sustainable forest management. The heterogeneity evaluation method breaks through the traditional analysis method of forest spatial structure. The heterogeneity index comprehensively and realistically describes the characteristics of spatial structure, and also quantifies the goal structure of forest spatial neighborhood relation and optimized spatial structure. The method has both forestry and ecological significance on optimizing and adjusting the existing forest spatial structure of Dongting Lake, on transforming large single plantation which mainly consists poplar and willow, and on restoring the functions of Dongting Lake ecological system, such as nourishing and cherishing water, conserving soil and water, reinforcing dam and so on. At the same time, the proposed method in this paper has provided a new way to establish and express ideal spatial structure for other regional forest management.