Study On Species Diversity And Interspecific Associations In Natural Restoration Woodland On The Northern Slope Of Qilian Mountains

Qilian mountains as the transitional zone between Tibetan Plateau, Inner Mongolia Plateau and theLoess Plateau, where the terrain is complex, species-rich and the main forest types are the coniferousforests. Since the1950s, the forests of Picea crassifolia has been depleted after the long irrationalhuman activities such as logging or grazing disturbance. The wood vegetation community structuregradually trend to simple, ecological function has been declined, the vegetation types had beendegraded and changed to shrub, grassland and scattered Betula-Populus secondary forests. At the endof the1980s, the government began to execute the enclosed measure for protect these area forest. Sothe forest vegetation has recovering after large-scale cutting and showed a good restoring effect due tothe artificial update and fencing measures. In the background of global climate change, the forestvegetation rapid recovery process of this area will become a typical case for research the vegetationsuccession, and also provide reliable reference value for vegetation restoration and reconstruction ofother regional. However, the vegetation is how to recover? the species composition, diversity andinterspecific associations are how to change in the process of restoration succession? Only clearlyunderstand these questions, could help to us understand the process ecological succession and causes inthis disturbed woodland. In view of this, We have selected seven major natural succession communities,using the method of substituting spatial difference for time change and ecological quantity analysismodel analyzed the change of the community species composition, diversity and the relationshipamong the species in different successional stage. Results showed that:（1）Up to111species, which belong to39families and86generas, were investigated in thisresearch. The mainly function groups is Compositae, meanwhile temperate genera such as Rosaceae,leguminosae and Gramineae appeared in the region flora and dominant in vegetation composition, butthese families mainly focus on shrub-herb layers. With the community succession, the annual andbiennial weed(A) and perennial forbs(PF) under fluctuations but the shrubs and trees species continuesto increased, so the community structure gradually become complex, the plant functional groupcomposition tend diversification.（2）With the community succession, the key species (B. platyphylla and P. davidiana) graduallychanged the community habitat (especially illumination) which make different structure speciesreplaced frequently. Some drought-tolerant annual and biennial weed(A) plants such as Geraniumdahuricum etc. replaced by some perennial forbs(PF) plants which love humidity such as Polygonumviviparum and Carex lanceolata etc. Some wetland plants such as Lonicera kansuensis and Rosawillmottiae gradually become the dominant species in shrub layer. At the same time, these fast-growing trees(B. platyphylla and P. davidiana) also gradually replaced by Picea crassifolia.（3）The αdiversity in forest communities varied spatially in the following order: herblaye(HL)>shrub layer(SL)>arbor layer(AL). The species richness and diversity of arbor layer is farlower than the shrubs, and herb layer. The number of species and the Gleason index of shrubs, and herblayer were the greatest in Betula community(Ⅴ). The Simpson index and Shannon-Wiener index werethe greatest in Picea-Betula community(Ⅵ). The Evenness index was the greatest in Betulacommunity(Ⅴ), while the greatest value of the Dominance index was found in Picea crassifoliacommunity(Ⅶ). Overall, the αspecies diversity follow the intermediate species-richness hypothesis.（4） S rensen index was the lowest between Geranium dahuricum community andBetula-Populus community(Ⅵ), was the greatest between Betula platyphylla community(Ⅴ) andPicea-Betula community(Ⅵ). Cody index increases firstly, and then decreases with the communitysuccession, which reflected species replacement rate is faster at the early stage but slower at the latestage. Whittacker index continuously decreasing with the community succession, among Geraniumdahuricum community(Ⅰ) was the highest, Betula platyphylla community(Ⅴ) was the lowest.（5）The number of shrub species pairs with negative association was larger than that withpositive association except Betula-Populus community. The interspecific associations of major shrubspecies pairs changed during successional stages, which was not significant at the early stage, wassignificant or very significant at the middle stage and was null or not significant at the late stage. Theoverall association among shrub plants was negative at the restored shrub community and broad-leavedforest dominated by heliophytes, which was positive in Mixed coniferous dominated by heliophytes,and negative association was shown in Mixed coniferous and broad-leaved forest, but there waspositive association in coniferous forest dominated by mesophytes.（6）The number of shrub species pairs with negative association was larger than that with positiveassociation except Geranium dahuricum community and Betula platyphylla community. Theinterspecific associations of major herb species pairs tends to be complex during successional stages.The overall association among herb plants was positive at Geranium dahuricum community, which wasnon negative at Potentilla glabra shrub community, was significantly negative at Populus davidianacommunity and broad-leaved forest dominated by heliophytes, was non negative at Betula platyphyllacommunity, but there was non positive association at Mixed coniferous and broad-leaved forest andconiferous forest dominated by mesophytes.