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鄄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

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Floral nectar provides crucial energy sources for diverse animals, many flowering species produce nectar to reward flower visitors, which provide pollination services for flowering plants. In addition to sugars and amino acids, the nectar of many plant species often contains secondary compounds such as alkaloids and phenolics, which are associated with plant defense against herbivores. The composition of nectar may influence an entire assemblage of local visitors and animal鄄 pollinated plants, but the basis for nectar resource selection is complex. Species co鄄existence and community assembly mechanisms depend on links between consumers and resources. A previous feeding trial showed that a sugar solution can motivate honey bees to use nectar containing plant defense chemicals (toxic nectar). Toxic鄄nectar plants are thus expected to be tightly linked with other non鄄toxic or less toxic floral resources for sharing pollinators, while general impacts of toxic nectar on plant communities have been little investigated. Most previous studies of the ecological and evolutionary significance of nectar secondary compounds have focused on the benefits to the plants that produce these compounds. For example, feeding experiments have shown that honey bees prefer to collect nectar containing secondary compounds.