Ziwuling Association Of The Arboreal Community

Loess Plateau is one of the regions where ecological degradation is the most serious in China. The soil erosion,vegetation wreck,and environmental pollution,frequent natural disasters such as droughts and floods,dust storm have made the ecosystem of Loess Plateau into the edge of collapse, which is not only threatening its own development but also effecting its adjacent region even the whole country.Thus,many domestic and overseas ecological scholars have done further research on how to protect,restore and rebuild the ecosystem of this area.All of these researches were based on the interspecific relationship which is one of the main characteristics of community.Only understanding the relationship of species in this area,can we offer some practical theory for protection and restoration.The interaction between(among) species leads to different resource utilization,and niche theory is the primary principle about the resource utilization status of species. Niche theory has been applied to researching the relationship of species,community structure and species diversity.Field sampling is one of the most common methods in ecology research.No matter which forms of field sampling,we must have a reasonable quadrat area.In this dissertation,we discussed the reasonable quadrat size for investigating interspecific association in forest community in Ziwu Mountain and researched the relationship between interspecific association and stability of community along succession series.At last,we compared the differences between natural P.tabulaeformis community and plantation P.tabulaeformi community in interspecific association and niche.The results are as follows:1.Total number of species pairs which didn't exist synchronously in a given quadrat size(Na) was put forward.Researchers often only attached importance to the phenomena that two species appeared in the quadrat area at the same time or alone but ignored that both the two species were not exist in the quadrat.Aimed at the number of species pairs,Na quantified the number of species pairs in a given quadrat area which species don't exist synchronously,and it could effectively make up the deficiency in the past research.The results showed that reasonable quadrat area could be confirmed by Na's variation range and tability visually.2.A series of parameters includingχ²-test,interspecific association(AC),Person's correlation coefficient(r),variance ratio(VR) and Na were used to study the interspecific association and their relationships with quadrat sizes of the dominant tree species in Q.wutaiensis community.The fluctuation of Na was the smallest when the quadrat size was 100 m²～200 m² and the number of quadrat was 40～80.Theχ²-test and AC analysis showed that significant interspecific association only appeared at the quadrat size of 25 m² and 50 m².Person's correlation analysis displayed that there were significant interspecific associations at the quadrat size from 25 m² to 200 m²,but the r value changed steadily at the quadrat size from 25 m² to 100 m².However,VR couldn't disclose the overall association of multi-species at different quadrat sizes.In order to reveal the relationships between species pairs more exactly,the quadrat size should be 100 m²,and the number of quadrats should be 45.Under such conditions,the interspecific association of the tree species in Q.wutaiensis community could be measured objectively.3.The important values of the dominant species such as B.platyphylla,P.tabulaeformis,Q. wutaiensis were higher than the others in respective community and the interspecific associations between them were not significant.Along with the succession of community,VR changed from negative to positive,but all of them were not significant.The proportion of species pairs which had the low absolute values of AC and r increased and the intensity of association became weak gradually with the progress of succession.The number and proportion of species pairs which associated significantly reduced,furthermore,most of those species pairs associated positively. Every community was stable relatively.Interspecific association was the loosest and stability was the highest in Q.wutaiensis community.The results suggested that the degree of interspecific association between species became infirm at present.The tendency of VR was towards positive but not significantly in the local forest communities.Thus,the Q.wutaiensis community has not reached the stable state,we still should protect the local natural vegetation for a long time.4.VR analysis showed that the correlation among species in plantation P.tabulaeformi community was negative and the one in natural P.tabulaeformi community was positive.There were more species pairs which associated significantly in natural P.tabulaeformi community than those in plantation P.tabulaeformi community,furthermore,most of those species pairs associated positively. This indicated that natural P.tabulaeformi community had a higher stability than plantation P. tabulaeformi community.The correlations between P.tabulaeformi and most other species were negative both in plantation P.tabulaeformi community and natural P.tabulaeformi community, which displayed that there were strong competition and rejection effects between P.tabulaeformi and its companion species.The niche breadths of P.tabulaeformi and Q.wutaiensis were relatively high and the O_ik between them was also high in the two different communities.This suggested that P. tabulaeformi and Q.wutaiensis had strong adaptability to microenvironment.To conclude,Na can provide some valuable reference for determining a reasonable quadrat area when we research interspecific association.In order to reveal the relationships between(among) species on Loess Plateau more exactly,the quadrat size should be 100 m².Along with the succession of community and the improvement of its stability,the degree of interspecific association between species became infirm,the tendency of VR was towards positive.Natural P.tabulaeformi community was more stability than plantation P.tabulaeformi community at present.The relationships between dominant species and its most companion species were negative and most O_ik between them were high both in Natural P.tabulaeformi community and plantation P.tabulaeformi community.In a word,the higher the stability of community is,the lower the relationship between species is.Positive interaction between species usually leads to a high niche overlap,while negative interaction often results in a low niche overlap without any influence of niche breadth.