Primary Studies On Insect Diversity Of The Vegetation Restoration Areas In Loess Hilly Region

The insects were investigated from March 2004 to November 2004 in Zhifanggou area on the loess plateau in China, and the characteristics indexs of the communities, the principal component analysis and WORD's clustering were used for studying the structure and diversity of the insect community in different vegetation. The results show that the insect community in 8 types of vegetation contains 14 orders, 76 families,341 species. More species of orders are colecptera , Lepidoptera and Hymenoptera. Family numbers and species number of the insect community have different changes, and insect species number of natural bush forest of natural arbor forest are respectively that the 124 and 132, both were more than mixed forest and simple forest ,the order of insect species number were natural closed forest, mixed forest and simple forest. Species and individuals of Carabid in the natural closed forests were higher than that in mixed forest and simple forest,so the natural closed forest play a pivotal role in protecting the carabids. The season changes of species and individuals number of the insect community in various vegetations can be described by a function:y=ax~3+bx~2+cx+d,and the insects were chiefly occurred. from May to September. The insect species varied spatially in the following order: the natural closed forests , the mixed forests, and simple forests. The individuals number of the insect community in Caragana mocrophylla and Periploca sepium were higher , and the major cause was that two simple forests appeared two kinds of harm serious pests which were respectively Apion sp.and Pontania sp, followed by mixed forests, Hippaphae rhamnoides L, and Robinia pseudoacacia, the insect numbers of the natural closed forests were smaller. The order of diversity value of the insect community in various vegetations from May to September were the natural closed forests, the mixed forests and simple forests, and the diversity value in various vegetations achieve the maximal value from October to September, the value of the natural closed forests is form low to high and from high to low, the value of the mixed forests and simple forests show unstable wave .The evenness value's change range of the simple forests and mixed forests are higher, and the natural closed forests are smaller. Contrary trend are assumed in the dominance values and the evenness values in time course. The species number of Colecptera , Lepidoptera and Hymenoptera are higher in different Order. the species number of the insect were the highest in the natural closed forests, the lowest in simple forests and the middle in the mixed forests. The individuals number of insect community in the natural closed forests were more evenness , the mixed forests took second place and the simple forests took third place. In Lepidoptera,Hemiptera,Diptera,Homoptera,Araneae and the others, the sequence of the insect diversity value in various vegetations were the natural closed forests, the mixed forests and the simple forests. In Colecptera,Hymenoptera, the value of the natural closed forests were the higest too.In Lepidoptera,Hemiptera,Orthoptera,Diptera,Homoptera,Araneae and the others,the sequence of the insect evenness value in various vegetations were the natural closed forests, the mixed forests and the simple forests, and in Colecptera,Hymenoptera the evenness value of the natural closed forests were the higest too; Contrary trend are assumed in the dominance values and the evenness values of different Order. the dominance value of the natural closed forests were lower than other vegetations, and the largest values of different Order are in the simple forests. There is obviously difference in guild groups of various vegetations. The phytophagous group is common dominance group, and species and individuals were the highest in different function groups. The order of the incect number in various vegetations were Caragana mocrophylla,Periploca sepium,Hippaphae rhamnoides L+Caragana mocrophylla,Robinia pseudoacacia,Populus davidiana+Robinia pseudoacacia,Hippaphae rhamnoides L,Natural arbor and Natural bush..The order of the diversity value of different guild groups in various vegetations were the natural closed forests, the mixed forests and the simple forests. The change of the evenness value in the natural closed forests were the smallest, the mixed forests were in the middle and the simple forests.were the highest. the sequence of the dominance values were the simple forests, the mixed forests and the natural closed forests. The order of the whole characteristics indexs of the insect communities in various vegetations were the natural closed forests, the mixed forests and the simple forests.The change of the diversity value were analogous to the evenness value ,and opposite to the dominance values. Therefore the natural closed forests has more inference on the insect community construction ,it make the insect community more abundance , complexity ,the change of mumber more placid,the diversity value higher, and the dominance lower In clustering, The analysis showed the insect community in natural arbor and natural bush gathered ,and two kinds of mixed forests also gathered. Simple forests in time course have not clear trend, but they were gathered for one kind in different Order and guild. The principal component analysis ang d were used for studying main factors and the temporal patterns of the insect communities in different time ,the results show that the insect commuonty in the natural closed forests had a more complicated composition ,lessfluctuation ,more obvious mian factors and temporal patterns. In the mixed forests and the simple forests, the composition of the insect commuonty were simple and fluctuated greatly ,their mian factors and temporal patterns were not obvious. the ratio of species number in different time and corresponding individual ,the ratio of the species number of plytohagous insect and natural enemy, and the ratio of the individual of plytohagous insect and natural enemy showed that The proportion of The enemy group in the insect communities were increased in the natural closed forests, and individuals in different species were more evenness, the relationship of insect species more complicated and profoundly, and makes the stability strengthen, increased the buffering ability. The insect community in simple forests were opposite to the natural closed forests, and the stability is the wrongest, The mixed forests were more stability than simple forests...