| Whether the forest structure is reasonable or not is very important for the long-term maintenance of its productivity and the stable exertion of its ecological service function.One100 m×100 m(PLS)and two 50 m×50 m(HTL-A and HTL-B)plots were set up in Pailuo Mountain,Ruili and Huatao Ridge,Mangshi,respectively,at Dehong Prefecture,Yunnan Province.The former stand was naturally regenerated after clear-cutting in 1958,while the other was formed on abandoned land after slash-and-burn cultivation in 1967.Simpson index,Shannon-Wiener index and Pielou index were used to analyze the species diversity,spatial structure parameters such as uniform angle index,neighborhood comparison and mingling degree were used to analyze its spatial distribution,O-ring function was used to analyze the distribution state of stand spatial point pattern and the spatial correlation between species;and intraspecific and interspecific competition intensities of Betula alnoides were analyzed by Hegyi competition index.The purpose of this study was to reveal the non-spatial characteristics of natural B.alnoides forest such as species composition and diversity,tree diameter structure,as well as spatial properties including species spatial distribution and spatial relationship,and provide fundamental evidences for the protection and management of natural B.alnoides forests and multifunctional management of its plantations.The main research results were as follows:(1)The species compositions in the study areas were rich and diversified.Species in family Lauraceae was the most abundant tree,and species in Ardisia was the most abundant shrub.There was no absolutely dominant species in PLS stand,and the species with the highest important value was Machilus pingii(14.76±4.96%)in PLS,followed by B.alnoides(9.55±5.46%).The species with the highest important value in HTL stands was B.alnoides(26.47±6.47%),which was absolutely dominant in the stand.Species richness(except herb layer),Simpson dominance index,Shannon-Wiener diversity index and Pielou evenness index in each layer of PLS stand were higher than those of HTL stands,but species dominance was lower in PLS stands.The species distribution was more evenly distributed in PLS stand.Simpson dominance index,Shannon-Wiener diversity index and Pielou evenness index were the highest in shrub layer,while the highest species richness was observed in tree layer.The curves for diameter-class structure of the stands were inverted J-shaped,and the main tree species were concentrated in the middle and small sized classes except B.alnoides which was in large and middle-sized classes.(2)Spatial structure parameters were analyzed for the stand using the 4-tree adjacent tree method.The results showed that the species were randomly distributed in PLS,HTL-A and HTL-B stands,and the proportion of randomly distributed trees was over 47%.Betula alnoides was distributed uniformly in PLS stands(0.5385),and was aggregated in HTL-A(0.4063)and HTL-B(0.4769)stands.The ratio of tree size in stand was evenly distributed in each grade,which was close to the golden mean on the whole.The tree species with average ratio in the range of(0.50,0.75] accounted for the largest proportion,and the average ratio of B.alnoides is less than 0.13;The results of average mixed degree of stand showed that the tree species in the forest were mainly of intense mixture.The average mixed degree of B.alnoides was greater than 0.73,and the spatial isolation degree was high;and the results of trivariate parameter distribution analysis showed that the distribution frequency was the highest for trees with random distribution(W=0.5),absolute dominance(U=0)and extremely intense mixture(M=1)in each stand.(3)The results of point pattern analysis showed that in PLS stands trees were clustered at scales of less than 28 m,and tended to be randomly distributed with the increase of scale,and in HTL-A and HTL-B,trees were randomly distributed at whole scale;the population of B.alnoides was mainly distributed randomly.The results of different zero hypothesis models showed that middle-diameter,large-diameter and extra-large-diameter trees of B.alnoides were mainly uncorrelated spatially.Based on the complete stochastic model(CSR),trees of different diameter classes were uncorrelated with each other in PLS and HTL-B stands,but negatively correlated in HTL-A stands at some scales(<20 m).Based on the heterogeneous poisson model(HPP),trees of different diameter classes were irrelevant in PLS stands,negatively correlated with each other in HTL-A stands at some scales,and positively correlated with large diameter trees at scale of less than 6 m in HTL-A and HTL-B stands.The spatial relationship between the main species and B.alnoides wais mainly unobvious,and the negatively spatial correlation was mainly concentrated in the middle to large scales;and positively spatial correlation was mainly concentrated in small scales.(4)The Hegyi competition index was used to analyze the competition intensity of B.alnoides.The competition pressure of B.alnoides population mainly came from interspecies,and the competition intensity gradually decreased with the increase of diameter at breast height(DBH).The interspecific competition pressure on B.alnoides varied with different associated tree species,and the competition index of Machilus pingii is the largest in PLS forest,followed by Castanopsis hystrix.The competitive pressure of HTL-A mainly came from Schima superba,followed by Lindera caudata and Alnus nepalensis.S.superba is the most competitive tree species in HTL-B,followed by L.caudata and C.hystrix.The effects of competitive trees on DBH of B.alnoides obeyed logarithmic function,and there was a significantly negative correlation between DBH of B.alnoides and competition intensity,and the competition intensity changed little when DBH above 40 cm. |
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