| The spatial pattern and correlation of plant species are the results of biological characteristics,plant competition relations between different species and environmental factors,which have caused the widespread attention by the ecologists for long time.Scholars try to understand the evolution of population formation,development and extinction by means of pattern analysis of plant population so as to reveal the position and function of population in the process of community substitution.The population structure refers to the distribution of the different sizes number in the population,which can not only reflect the combination condition of individuals to different populations,but also reflect the population dynamics and development trends.The process of population structure transformation caused by heterogeneous habitats,which has made adaptive adjustment of population structure,and also led to different size of individual configuration status change,thus making the individual differences in the ability to occupy the resources environment and the size of the space.It directly reflects the adaptive mechanism of the survival of the fittest under the environmental screening,and has an important impact on the spatial pattern of the population.At present,the research of Tamarix chinensis mainly focuses on the morphology and taxonomy,physiological and ecological characteristics,the maintenance mechanism of population structure,the distribution of spatial pattern,the mechanism of salt tolerance and drought.While the researches on small scale point population size structure of Tamarix chinensis pattern and its relevance are relatively limit,especially on the understanding of different groundwater environmental gradient under the influence of the wetland of Tamarix chinensis individuals inside the intra and interspecific competition and environmental plasticity mechanism is still weak.In view of this,in Qinwangchuan Wetland National Wetland Park in salt marsh,selecting different size grades of Tamarix chinensis as the research object,using the coenology survey method and point pattern analysis method,analyzing the different stages of development of Tamarix chinensis in different groundwater depth gradient under the influence of the small scale pattern and space relevance so as to systematically explore the dynamic characteristics of the establishment and development of Tamarix chinensis,and to reveal the change process of population structure and spatial pattern of Tamarix deeper groundwater environment evolution.The results showed that:(1)With the groundwater depth increasing gradually,the height of the community showed a gradually increasing trend,and the community density showed a trend of decreasing first and then increasing.Tamarix chinensis population density showed a trend of increasing first and then decreasing.While the number of branches showed the opposite trend: the plant height gradually increased,the small plant(seedlings and saplings)ratio gradually decreased,while the proportion of the plant(big trees and big trees)gradually increased.(2)With the groundwater depth increasing,Tamarix chinensis herb species richness index,Shannon-Weiner diversity index and Simpson dominance index showed a decreasing trend,while Pielou evenness index showed a trend of increasing first and then decreasing.With the increase of the gradient of the buried depth,the coverage of the ground covered by the ground decreases first and then increases,while the thickness of the killed layer shows the trend of increasing first and then decreasing.In the sample plots II,III and IV,relatively,the higher the coverage,the smaller the seedling density,the thicker the thickness of the shoot and the higher the seedling density,and the density of the seedlings in the sample ground was limited by the ground cover layer.(3)In the shallow land of sample I,the size-class structure of Tamarix chinensis showed an increasing pattern;as the groundwater depth of sample II was decreased,the size-class structure of Tamarix chinensis population was stable;with a further decline of groundwater depth,the size-class structure of Tamarix chinensis showed declining type.(4)During the process of the increasing of groundwater level,the spatial patterns of Salix populations at different stages of development have been adaptive,the spatial distribution pattern of Tamarix chinensis seedlings by mesoscale agglomeration to smaller scale aggregation transformation,transformation of aggregation distribution pattern of trees from larger scale to smaller scale,the aggregation scale of the spatial pattern of species in middle tree expanded to larger scale and then gradually turned to random distribution,the big tree presented the pattern of "random accumulation homogeneous".(5)The spatial association between Tamarix chinensis population in different stages of salt marsh wetland has complicated scaling characteristics.Salt stress higher groundwater environmental gradient,the development stages of Tamarix chinensis showed a favorable correlation with each other;abundant resources and environment for the survival of groundwater depth environmental gradient II.Among the various developmental stages of tamarisk mainly for not related;in the groundwater depth deepen environmental gradient III and IV,mainly presented as negative or no correlation between different developmental stages of Tamarix chinensis.The structure and spatial pattern of plant populations were limited by the spatial arrangement of individual plants of different sizes.The diversity of tree species with different sizes was affected by the heterogeneity of resources and environment.And the plant height and plant density changed,and then promoted the population to form a unique spatial structure at a certain scale.The changes of plant population structure and individual competition under environmental heterogeneity are the key factors for scale transformation of spatial patterns and the correlation at different stages of population development,which reflected the update of salt marsh plants in response to groundwater depth and succession mechanism. |
PDF Full Text Request