Study On The Stand Diameter Distribution And Spatial Structure

The object of this research is the arbor forest of Caodun sample plots in Xingcun Town,Wuyi City in Fujian Province.The main tree species are Castanopsis eyrei,Syzygium buxifolium,Lithocarpus harlandii,Ilex fukienensis and Ilex chinensis in this forest.According to the observation data of 12 representative sample plots,the following four probability density functions:Weibull distribution,normal distribution logarithmic normal distribution and Logistic distribution are used to study the diameter distribution regularities of the arbor forest with two centimeters and four centimeters of diameter class.Through X~2 test,the simulating effects of the four probability density functions to describe the tree diameter distribution laws are tested and the most suitable fitting probability density function is chosen to construct parameters estimated models.With ArcGIS Tyson polygon generation tool,generating the Voronoi polygon distribution map and analysis the corresponding spatial structure after identifying the main species and eliminating edge effects.Neighborhood comparison,angle index,diversity mingling and competition index are calculated to based on the Voronoi diagram and the stand conditions are respectively analyzed by the four stand spatial structure parameters.The main conclusions are as follows:(1) Using the four four probability density functions with two centimeters and four centimeters of diameter class to fit the selected eight sample plots one by one,the result shows that when the diameter class is two centimeters,the acceptance rate of Weibull distribution reaches 75 percent because there are six plots in the eight plots through X~2 test successfully,the effect is better than other distribution density functions;when the diameter class is four centimeters,the acceptance rate of Logistic distribution is the largest,the effect is the best.(2) Parameters estimated models for scale parameter b and shape parameter c are respectively built according to the most suitable Weibull distribution density function with two centimeters of diameter class to predict the stand diameter distribution.The compliance rate was50% after X~2 test.(3) Neighborhood comparison shows that the situation of the DBH size of the main tree species in the study area is between bad state and sub dominance.The growth of Castanopsis eyrei DBH is at an advantage state,in accordance with the growth trend in vertical direction.(4) Angle index shows that the majority of the main tree species is in clumped distribution in their own spatial structure unit,individuals in randomly distributed are the least.The clumped distribution of Lithocarpus harlandii is the highest proportion in the total.(5) Diversity mingling shows that the degree of isolation fixes on a highly mixture and intensive mixture,and high intensive mixture accounts for the majority,moderate mixture accounts for the less and there are no zero and weak mixture.Over half of Lithocarpus harlandii and Castanopsis eyrei are in the state of high intensive mixture in their own spatial structure unit.(6) Competition index shows that the statistics of Castanopsis eyrei is the least and the nearest neighbor wood on the competition disturbance is also the minimum.Ilex chinensis has the highest competition index that shows the competition is the most intense in the forest spatial structure unit and the competition is the largest.