| In order to fully understand and master the dynamic characteristics of community types,species diversity,biomass allocation and its impact factors of undergrowth vegetation in the secondary forest of Quercus aliena var.acuteserrata in Qinling Mountains,we selected three typical areas that were Tongtianhe National Forest Park,the Zhouzhi National Nature Reserve,and the Taibai Mountain National Nature Reserve.Based on the line transect method and typical plot survey,finally we obtained 30 sample sites of data.On this basis,the community classification and ordination,the elevation pattern of species diversity and biomass,the effects of density of stand and soil factors on species diversity and biomass,the relationship of species and biomass were analysed and researched in this study.Main conclusions are as follows:(1)The numerical classification analysis of understory vegetation was carried out by MRT,the undergrowth vegetation in the secondary forest of Quercus aliena var.acuteserrata in the study area was divided into three types by cross-validation and plant community classification and naming principles: Symplocos paniculata +Viola arcuata,Litsea pungens+Elymus kamoji,Smilax china+Rubia cordifolia.The results of CCA ranking plots and environmental factors showed that the three communities exhibited a regular distribution.The four environmental factors,such as altitude gradient,total nitrogen content,organic matter content and total potassium content,had significant effects on the distribution of undergrowth vegetation in natural secondary forest communities in the study area.(2)The variation trend of species richness and Shannon-Wiener diversity index in shrub layer and herb layer in the secondary forest were basically the same,it expressed as the shrub layer slightly higher than herb layer,Simpson dominance index and Pielou evenness index were not much different,and the trend were relatively flat.The Species richness,Shannon-Wiener diversity index,Simpson dominance index and the Pielou evenness index of the undergrowth vegetation were basically consistent along the elevation gradient,showing a single peak model,it reached a maximum value of 1600-1700 m,then decreased.The Pielou evenness index in shrub layer had no correlation with the elevation gradient.The relationship between species diversity index and forest density in shrub layer and herb layer were basically the same,Species richness,Simpson dominance index and Shannon-Wiener diversity index all decreased with the increase of stand density,except that the Pielou evenness index.The correlation between species diversity index and soil nutrient in shrub layer was mainly reflected the relationship of total potassium content and species richness and Shannon-Wiener diversity index.There was no significant correlation between the species diversity index of the undergrowth vegetation and the soil nutrient.(3)The biomass in shrub layer under the secondary vegetation of the Quercus aliena var.Acuteserrata forest in the Qinling Mountains was much higher than herb layer,the proportion of shrub layer biomass reached 74.825% in the total biomass of undergrowth vegetation,it was about three times the amount of herb layer biomass.The distribution regular pattern in shrub layer biomass of various organs was showed that branch more than root than leaf,the biomass of the underground part in the herb layer was higher than the aboveground part.The effect of elevation on the biomass in shrub layer presented a single peak model,below 1700 m above sea level,biomass increased with altitude,it reached a maximum value of 1700 m,then gradually reduced.The biomass in herb layer decreased with the increased of elevation.As the stand density increased,the biomass in shrub layer decreased.There was no significant relationship between the biomass and stand density in the herb layer.The relationship between the biomass of undergrowth vegetation and soil nutrient showed that the biomass in herb layer was significantly positively correlated with the total potassium content of the soil.Other than this,there was no significant correlation between the remaining soil nutrients and the undergrowth vegetation biomass.The biomass and Species richness in shrub layer and the Shannon-Wiener diversity index were significantly positively correlated.However,there was no correlation with the Simpson dominance index and the Pielou evenness index.And that there was no correlation between the biomass in the herb layer and the four species diversity indices. |
