Spatial Structure And Its Effects On Stand Growth In Different Proportions Mixed Plantations Of Pinus Massoniana And Schima Superba

The spatial structure of stand has an important influence on the growth of forest.4 types-type Ⅰ（contrast,ten Pinus massoniana）,type Ⅱ（eight Pinus massoniana and two Schima superba）,type Ⅲ（seven Pinus massoniana and three Schima superba）and type Ⅳ（six Pinus massoniana and four Schima superba）,which were divided according to the proportions of tree species,were selected to set the sample plots which composed of the aerially seeded Pinus massoniana.The spatial structure parameters and growth indexes of different types of stands were calculated through the data obtained from the sample-plot survey.The growth status and spatial structure characteristics of different types of stands were analyzed and compared.The relationships between the spatial structure characteristics and the growth of stands were discussed.The results can provide reference for the structure adjustment,optimization and scientific management of the aerially seeded Pinus massoniana plantations.The main results and conclusions were as follows:（1）From type â…  to type â…¢,the average diameter at breast height（DBH）,average tree height,average volume of individual tree and accumulation volume of Pinus massoniana decreased gradually,while from type â…¢ to type â…£ increased.From type â…  to type â…£,the average crown size showed a trend of decreased first and then increased then decreased.Except for the DBH of type â…¡,the average volume of individual tree was significantly lower than that of type Ⅳ（P<0.05）,and the volume of accumulation was significantly lower than that of type Ⅰ（P<0.05）.There was no significant difference among other factors（P>0.05）.Among the three mixed plantation types,the volume of Schima superba in type â…¡ was significantly lower than that of type â…¢ and type Ⅳ（P<0.05）.There was no significant difference among other factors（P>0.05）.The average tree height,average crown width and average volume of individual tree of each diameter grade of Pinus massoniana and Schima superba were all increased with the increase of diameter grade.The coefficients of variation of different growth factors were different.The coefficients of variation of average DBH were small,while the accumulation volume was large,and the coefficient of variation of Schima superba was greater than that of Pinus massoniana.（2）The average intraspecific competition index of Pinus massoniana was in the order of type â… >type â…¡>type â…¢>type â…£.In all diameter classes,there was a significant difference between type â…  and type â…¡,type â…¢,type Ⅳ（P<0.05）,while there were no significant difference between type â…¡,type â…¢,type Ⅳ（P>0.05）.The average interspecific competition index of type â…¡ and type â…¢ were significantly different from that of type Ⅲ（P<0.05）,while there were no significant difference between type â…¡ and Ⅲ（P>0.05）.Among the type â…¡,type â…¢ and type â…£,the percentage of intraspecific competition index of Pinus massoniana in total competition index were 83.95%,80.24%and 60.84%,respectively.The best fitting models between the total competition index,intraspecific competition index,interspecific competition index and DBH of Pinus massoniana were power function or exponential function.There was a negative correlation between competition intensity and DBH,when DBH was smaller than 25 cm,the competition pressure of Pinus massoniana was greater.（3）The average angular scale and frequency distribution of different types of Pinus massoniana were similar.The average angular scales of type I to type IV were 0.468,0.476,0.477 and 0.467,respectively.There was no significant difference among different types（P>0.05）.The whole stand and trees of different diameter classes were mostly evenly distributed or randomly distributed.The average mixed degree of Pinus massoniana increased with the increase of the mixed proportion,and type â…¡,type â…¢ and type â…£ were mainly distributed randomly.The average mixed degree of type â…¢ to type â…£ were 0.173,0.276 and 0.462,respectively.There was significant difference between type â…¡ and type Ⅳ（P<0.05）.Most of the trees were in weak mixed or medium mixed degree,and the average mixed degree of each diameter class increased continuously with the increase of diameter class of Pinus massoniana.The average open degree of Pinus massoniana from type â…  to type â…£ were 0.236,0.318,0.342 and 0.255,respectively.The growth space of the whole stand and the trees of all diameter classes were insufficient or basically sufficient,and the average openness of type â…  and type â…£ were significantly different from that of type â…¡ and type â…¢ respectively（P<0.05）.（4）Competition index and angle scale decreased with the increase of average DBH,average tree height,average crown diameter and average volume of individual tree.Competition index had a significant negative correlation with average volume of individual tree,while angle scale had no significant correlation with all factors.Mixed degree and average volume of individual tree had a positive significant correlation.Openness and volume had a negative significant correlation.The regression model of average volume,competitive index and mixed degree was:y=0.069-0.011x₁+0.067x₂,which has significant linear regression relationship;the regression model of volume and openness was:y=121.289-216.969x,which has significant linear regression relationship.