Small scale point pattern analysis based on different null models for detecting spatial patterns of dominant species in Sanjiang Plain,China
Marsh was the major wetland type.The soil of marsh is oxygen poor due to permanently inundate which has formed a special environmental conditions and vegetation types.The Sanjiang Plain is one of the largest freshwater marshes with area of approximately approximately 10400km2.The dominant plants are grass species which both have cloned habits such as Carex lasiocarpa,Carex pseudocuraica,Deyeuxia angustifolia and Glyceria spiculosa.To study the spatial distribution pattern of plant populations in marsh is supplementary for spatial pattern theory because the distinctive environmental conditions.Meanwhile,it is very significance for revealing plant populations characteristics in marsh environment.Thus,we analysis the spatial distribution pattern of main dominant species(C.lasiocarpa,C.pseudocuraica,D.angustifolia and G.spiculosa) by point pattern analysis based on different null models.The study site is located at the Ecological Experiment Station of Mire Wetland in Sanjiang Plain,Chinese Academy of Sciences(47deg35' N,133deg31'E,56 m above sea level),Northeast of China.In September 2012,we mapped a 4 x 4 m representative area in thepermanently inundated marsh community which the surface are smooth and have uniform physiognomy.The plot was divided into 256 contiguous 25 x 25 cm quadrats,as the basic unit of vegetation survey,using the bamboo pole and the white rope.The relative position of each plant individual or plexus projection of grass was expressed in the coordinates which represent the distance.All analyses were conducted using the grid based estimators in the Programita software package.Nineteen Monte Carlo simulations were used to generate 95% confidence envelopes.Our results showed that:The four main dominant species mainly depart from complete spatial randomness(CSR) and shows aggregation in 0 200cm scales,but have varying degrees of deviation; The C.lasiocarpa,C.pseudocuraica and G.spiculosa depart from poisson cluster process(NS) in small scale,except D.angustifolia; The C.lasiocarpa and G.spiculosa depart from nested double cluster process(DC) in a very small scale,but not significant.The C.pseudocuraica accordance with nested double cluster process in0 200cm scales,completely; The measured value of population farther departed from complete spatial randomness(CSR)are more likely accordance with poisson cluster process(NS),and farther depart from poisson cluster process(NS) are more likely accordance with nested double cluster process(DC) The aggregation of 4 species in 0 200cm scales is caused by vegetative propagation which could help to adapt the perennial water environment.Much ramet system can form a cluster in large scale,while the one ramet system forms a cluster in small scale.On the other side,the aggregation intensity of population would reduce due to strong intraspecific competition in has formed cluster.