| Forest gaps,as an important mode of disturbance in forest communities,has an important impact on the composition of understory species.The research on the relationship between the spatial pattern of forest canopy gap and its characteristic index and the diversity of understory plants is of great significance to explore the different forest canopy gap characteristics index for the growth of understory plants,which will further help understand the dynamics community and also act like a guiding role in protecting the species diversity.In this study,there were 4 research plots were randomly selected,which included three tropical rainforests and one monsoon evergreen broad leaved forest that were one hectare in the Xishuangbanna tropical rain forest.The light and small six-rotor UAVs were used to mount the Sony ILCE-A7r visible light sensor to obtain high-definition digital images of each plot.The digital surface elevation model and the topographic data of each plot are used to determine the distribution type of the forest canopy gap in each plot,and further extract the landscape pattern index of each forest canopy gap.Based on the basic survey data of surface quadrangle,a statistical survey was conducted on the plant diversity under different forest canopy gap in different areas,aiming to analyze:1)The characteristics of spatial pattern of forest canopy gap in tropical rain forest of Xishuangbanna prefecture;2)Whether the plant composition under the tropical forest in xishuangbanna prefecture is affected by the forest canopy gap that is different from plant composition under the forest;3)The influence from the spatial pattern of the tropical forest canopy gap affected the undergrowth plant diversity in xishuangbanna.Research shows that:(1)In the tropical forest of Xishuangbanna,the area distribution of forest canopy gap in the four sample plots all showed a negative exponential distribution pattern with a large number of small forest canopy gap and a small number of large forest canopy gap but a large total area;For spatial pattern of overall forest canopy gap,tropical rain forest sample canopy gap mean euclidean near-neighbor distance(ENN)are more than 10,compared with evergreen broad-leaved forest sample plots(DPZ)mean euclidean near-neighbor distance to the youngest,outside,relative to the three tropical rain forest sample plots(44,CC,SK)in forest gap,evergreen broad-leaved forest sample plots DPZ forest gap than in the distribution pattern of space.Forest canopy gap shape complexity,more than three tropical rain forests to shape complexity degree between 1.6-3 distribution,the average shape complexity index was 2.47,evergreen broad-leaved forest shape complexity degree distribution between 1.5 to 2.6,the average shape index was 2.19,tropical rain forest in Xishuangbanna tropical forest canopy gap shape more complex than the area evergreen broad-leaved forest.(2)In terms of plant diversity characteristics,first of all,four sample forest canopy gaps of xishuangbanna tropical forest,the number of plant species in the forest canopy gap was less than that in the same forest canopy gap,while the number of single species was more than that in the same forest canopy gap.Secondly,the species with the top 10 important values under various forest canopy gap are almost consistent with the species with the top 10 important values under various forest canopy gap,which shows that most forest canopy gap will recover towards the existing pattern of the same climax.Again,characteristics of plant diversity under forest canopy gap are shown that plant characteristics under the forest canopy gap is as same as plant configuration under the forest,but below the canopy gap contains many plant species,which shows that the effects of forest canopy gap formation were beneficial to the improvement of the understory plant diversity,but it didn't change the composition of the understory.(3)Among the three indexes calculated for plant diversity,species richness has an intuitive response between the spatial characteristics of forest canopy gap and the plant diversity under forest.There was a highly significant positive correlation between forest canopy gap area and species richness(P<0.001).In terms of the three tropical rain forest samples,the forest canopy gap area and species richness showed a highly significant positive correlation(P<0.01,R2 = 0.6),and the relationship curve showed a logarithmic growth.There was a significant positive correlation between the mean shape complexity index(MSI)and the diversity index under the canopy(P<0.05).The change of the spatial pattern of the tropical forest canopy gap in Xishuangbanna,such as the increase of the area and shape complexity,is conducive to improving the diversity of the understory plants.Moreover,in the tropical rain forest of this region,under the small forest canopy gap,the plant diversity under the forest is mainly limited by the influence of the forest canopy gap area,and the influence of the shape complexity of the forest canopy gap on the plant diversity under the forest is small.However,when the forest canopy gap area is large to a certain extent,the plant diversity under the forest is weakened by the factor of the forest canopy gap area,and the influence of the shape complexity of the forest canopy gap on the plant diversity under the forest is stronger than that under the factor of the forest canopy gap area,and the plant diversity under the forest is mainly affected by the two factors.To sum up,the research shows that in Xishuangbanna tropical forest:1)in terms of spatial pattern of forest canopy gap of three tropical rainforest plots and one evergreen broad-leaved forest plot,compared with that of evergreen broad-leaved forest plot,ENN value of three tropical rainforest plots is larger and forest canopy gap distribution is more dispersed than that of evergreen broad-leaved forest plot.The reason may be related to the ground water and heat condition,microbial activity and the composition of dominant tree species in the canopy;2)In terms of the characteristics of plant diversity under the forest canopy gap,the species with the top 10 important values under the forest canopy gap in the four tropical forest samples are almost consistent with the species with the top 10 important values within the sample,and all kinds of forest canopy gap tend to develop and recover towards the climax communities of the sample.The composition and configuration of plants under the forest canopy gap are consistent with plant composition under the forest,but their diversity is higher than that under the forest,it means the influence from the formation of the forest canopy gap is beneficial to the improvement of the diversity of plants under the forest,and this influence is in a small range and has little impact on the whole forest community;3)In terms of the relationship between the spatial pattern of forest canopy gap and the diversity of undergrowth plants,the characteristics indexes of the spatial pattern of forest canopy gap,such as the shape complexity index of forest canopy gap and the area of forest canopy gap,are significantly positively correlated with the diversity of undergrowth plants.Compared with the shape complexity factor of the forest canopy gap,the area of the forest canopy gap has a more significant effect on the plant diversity under the small forest canopy gap.When the area is large to a certain extent,compared with the area factor,the shape complexity index of forest canopy gap has a more dramatic impact on the diversity of understory plants.The reasons may be related to topography(such as slope,altitude)and closing mode of forest canopy gap.This study further deepened the understanding of the spatial pattern of the forest canopy gap in Xishuangbanna tropical rain forest and its relationship with the diversity of undergrowth plants,which can provide certain support and reference for similar studies in the future. |
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