| The forest communities of Quercus liaotungensis, as one of the most important localvegetation communities, has a large distribution range in the Loess Plateau, which mainlydistributes in the north of the Liaodong Peninsula-hilly areas, the mountain in northernHebei, south of Heng Mountain in Shanxi Province, Shaanxi and Gansu the Loess Plateau andwestern of Qinling mountain, etc.， and plays an irreplaceable role ecologically in these areas.Based on the distribution characteristics of Q. liaotungensis forest communities,192plots(20m×20m), involving6areas (Doling mountain, Lingkong mountain, Huanglong mountain,Ziwuling Region, Taibai mountain and Xiaolong mountain), have been arranged. From theselarge scale in Loss Plateau, the species composition, floristic geographical element, origin andevolution of the flora, community structure and physical characteristics, communityclassification, biological diversity, niche and relationship among main populations, regeneratecharacteristics of Q. liaotungensis forest, etc., have been discussed and concluded mainly asfollows:1. Composition and flora of the community species(1) Community composition of Ass.Q.liaotungensis forest are rich in plant species, inwhich there are507species of seed plants (including some varieties) from192plots of sixareas in all, belonging to76families,238genera (Engler system), accounting for51.7%offamilies,27.5%of genera,15.7%of the species in the Loess Plateau, and it is the one ofrichest forest communities in plant species in the loess plateau area. The coefficients of familyand genus are bigger than other flora, more species within fewer families, fewer specieswithin more families. In the flora, the families more than20species is only6.6%of wholeone, but the number of species from these families is31.8%of whole one; contrarily, thefamilies with only one species is about25.0%of whole one, but the number of species fromthese families accounts for merely3.7%of total species.(2) Community flora of Ass.Q.liaotungensis forest has obvious temperate nature, and atthe same time, is related to tropical and subtropical flora to some extent. The number of genusof temperate members distributing in the research area is67.1%of all genera of the flora. Those genera contain64.1%of all species, but one of tropical members in this area is only20.1%of the whole flora. The community flora with complex geographic compositions, somespecies form north and south and some species from east and west living here, is obvioustransitionally.(3) In the loess plateau, the Ass.Q.liaotungensis emerges before the pliocene, probablyoriginating from miocene to pliocene time, and pleistocene time could be the maindevelopment period. The community flora based on tertiary north China ancient flora hasformed community structure dominant by Ass.Q.liaotungensis through the interspecificcompetition and environmental adaptation.2Community structure and Physiognomy characteristics(1) The species composition and physical characteristics of Ass.Q.liaotungensis forestdominant species were both similarities and having different performance in the regions. Thepresence or absence in various areas of main species in Ass.Q.liaotungensis forest was relatedto the sites of the forest communities. The species-area curve model is good for the expressionof plant species richness regionally.(2) Species’ life forms of Ass.Q.liaotungensis forest community has obvious dominantposition with Ph (56-66%), which fully embodies the characteristics of forest community;Species’ life forms of community composition is obviously various among different regions.(3) There is a notable difference among six areas in species ecotypes in regional Quercusliaotungensis Communities. In the Xiaolong Mountain and Taibai Mountain,hygrophyte-mesophyte is more, xerophyte is lack, but xerophyte ratio is higher in the ZiwuMountain and Huanglong Mountain in the Loess Plateau.3. Types and Biodiversity of Quercus liaotungensis Communities(1) Based on the results of PCA two-dimensional analysis, the communities could beclassified into twelve association types in the Loess Plateau, namely Ass. Quercusliaotungensis+Fargesia spathacea+Phlomis umbrosa; Ass. Quercus liaotungensis+Smilaxstans+Smilacina japonica; Ass. Quercus liaotungensis+Lespedeza bicolor+Radixsanguisorbae; Ass. Quercus liaotungensis+Campylotropis macrocarpa+Melampyrumroseum;Ass. Quercus liaotungensis+Cotoneaster multiflorus+Poa nemoralis; Ass. Quercusliaotungensis+Rosa hugonis+Bothriochloa ischaemum; Ass. Quercus liaotungensis+Ostryopsis davidiana+Polygonatum kingianum; Ass. Quercus liaotungensis+Sophoradavidii+Bothriochloa ischaemum; Ass. Quercus liaotungensis+Spiraea pubescens+Dendranthema chanetii; Ass. Quercus liaotungensis+Hippophae rhamnoides+Agropyroncristatum; Ass. Quercus liaotungensis+Forsythia suspense+Radix Sanguisorbae; Ass.Quercus liaotungensis+Hippophae rhamnoides+Thalictrum aquilegifolium. (2) Biodiversity showed large differences between different communities, generally, thediversity index order is that T2>T1>T3>T11>T9>T7>T5>T12>T4> T10>T6> T8.(3) The biodiversity are closely related to the capacity of environment resources. Thesuperior the environmental resources of community is, the higher the biodiversity is, and themore abundant species are. The basic general order of the biodiversity index is that NSlopes>NW slopes>ES slopes>SW slopes> S slopes.4Dominant population niche researches(1) Q.liaotungensis, Betula platyphylla and Pinus tabulaeformis, which serve as theconstructive species of Ass.Q.liaotungensis forest in the loess plateau, occupied a larger nichebreadth in the tree layer. Their strong competitive edge for limited resources is the maindriving force for the community succession.(2) In the shrub layer, with a larger niche breadth, Spiraea pubescens, Rosa hugonis andOstryopsis davidiana become the major species of this layer in different types ofAss.Q.liaotungensis. These species are very important for the classification of thecommunities.(3) Carex lanceolata, which distributes as a cosmopolitan of the loess plateau, is themajor population of herb layer, and therefore, and exists nearly every sample plot investigated.Although occuping the largest niche breadth in the herb layer, it does little significance to thecommunity classification of Ass.Q.liaotungensis.5The analysis of interspecific association in communityThe interspecific association of the main trees and shrubs of Ass.Q.liaotungensis forestcommunity showed no significant positive association in the Loess Plateau. In730speciespairs,371pairs in positive association account for52.8%of the total,294pairs in negativeassociation account for41.8%, and38pairs in the unrelated account for4.7%(Jaccard index).44pairs have the correlation in very significant level or significant level (including positiveand negative).6Ass.Q.liaotungensis forest regeneration characteristics(1) Ass.Q.liaotungensis forest has two ways of generation, seedling and shooting. Themajor regeneration way is shooting in the serious disturbed forest, sunny slope and steepslope, but giving priority to seed regeneration in less disturbed forest, shady slope and gentleslope.(2) Seedlings in forest gap have more chance to be sapling than one under forest ofAss.Q.liaotungensis. The openness ranged from0.6to1.0of forest gap was more suitable tothe regeneration and their growing up.(3) The regenerative ability of Q.liaotungensis and the seedling growth on shady and half-shaded slope are significantly better than sunny and half-sunny slope in the Loess Plateauregion (excluding Taibai Mountain). The order of the density of natural regeneration seedlingswas N slope> E slope> W slope> S slope. |
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