| Dalbergia odorifera is an endemic species in Hainan and a second-level national protected plant.It is a common and precious redwood species in my country and has extremely high economic value.The increase in the planting area of Dalbergia odorifera and the single ecosystem have resulted in serious occurrence of Dalbergia odorifera leaf-eating pests.The large amount of feeding and excrement of the pests will affect the photosynthesis of the forest,the formation of Dalbergia odorifera heartwood is also seriously affected.The internal microenvironment of the forest represented by different aboveground layered structures is different.The existence of pathogens,the growth and feeding of pests are closely related to the ecological microenvironment.Based on the theory of forest ecology,this paper clarifies that the layered structure of Dalbergia odorifera plantation includes the relationship between the structure of stand layer and the structure of undergrowth shrub and grass litter layer and the occurrence of leaf eating pests,selects the key structural indicators that affect the occurrence of leaf eating pests,and constructs the prediction model of the layered structure of Dalbergia odorifera plantation based on the key indicators,so as to provide scientific guidance for ecological control of leaf eating pests and healthy management of plantation.The main results are as follows:(1)The relationship between the layered structure of Dalbergia odorifera plantation and leaf-eating pests.The forest hierarchical structure is mainly divided into two types of indicators:the non-spatial structure of the forest stand and the spatial structure of the forest stand.Select tree height,diameter at breast height,height under branches,average crown width,number of vertices,total leaf area per plant,and crown vertical complexity as non-spatial structure indicators,and select mixed degree and 3 size ratio indicators as spatial structure indicators,respectively Investigate and analyze their association with leaf-eating pests.It was found that among the non-spatial structure indicators,except for the vertical complexity of the canopy,there was a significant negative correlation between the remaining 6 structural indicators and the bite rate and population density of Dalbergia odorifera leaf-eating pests(P<0.01).Taking the plot factors into account and then performing redundant analysis,it is concluded that only tree height is the key indicator that affects the occurrence of forest pests(F=32.135,P=0.002).In the spatial structure index,the forest stand mixing degree value and size ratio value are mostly distributed between 0-0.5,that is,the overall forest tree mixing degree in the plantation is weak,and the growth dominance of individual trees is more balanced;correlation analysis shows that the insect population density and The degree of mixing,tree height and crown size ratio all showed a significant negative correlation(R2=0.882,P<0.05;R2=0.756,P<0.05;R2=0.866,P<0.05),but the correlation between breast diameter ratio and insect population density is not significant(R2=0.345,P<0.05).From a comprehensive point of view,in the sparse forest area and young forest area of Dalbergia odorifera plantation,select some native tree species or suitable foreign tree species for appropriate matching and planting,while increasing the tree height and tree height of Dalbergia odorifera forest as much as possible.The value of the size ratio is fundamentally effective in preventing and controlling the occurrence of leaf-eating pests.(2)The relationship between Dalbergia odorifera plantation shrub and grass litter layer structure and leaf-eating pests.From the community to the species itself,the Shannon index,Pielou index,average height,and shrub coverage are mainly used as the shrub structure indicators,and the litter thickness is used as the indicator for the litter layer structure.Investigate and analyze their relationship with eating leaves.The correlation between pests.After the average grading of each structural index,multiple comparisons found that the incidence of leaf-eating pests was significantly different between the first level of the average height of shrub and grass and the other four groups(2,3,4,and 5)(P<0.05)),when the height is 0-15cm,the occurrence of leaf-eating pests is the largest;the occurrence degree of leaf-eating pests is significantly different between the lowest and highest levels of shrub coverage and litter thickness(P<0.05),Among them,when the coverage is 0.8-1.0,which is the highest level,the bite rate and population density of Dalbergia odorifera leaf-eating pests are the highest;the occurrence degree of leaf-eating pests is significantly different between the levels of Shannon index and Pielou index(P<0.05).Correlation analysis shows that the Shannon index and Pielou index have a significant negative correlation with the insect population density(R2=0.782,P<0.05;R2=0.710,P<0.05),the average height of shrubs and grass,litter There is a negative correlation between layer thickness and insect population density,and a positive correlation between shrub and grass coverage and insect population density,but both are not significant(R2=0.070,P<0.05;R2=0.280,P<0.05;R2=0.104,P<0.05).On the whole,under the premise of mixed planting of Dalbergia odorifera plantation with multiple forest trees,it is advisable to choose heterogeneous trees and shrubs and grasses with insecticidal or insect repellent effects to plant them in a reasonable combination.In addition,when planting in the forest,it is necessary to ensure the coverage of shrubs and grasses and achieve the density.(3)The model of controlling the above ground stratification structure of leaf eating pests in Dalbergia odorifera was established.Stepwise analysis showed that the indexes affecting the insect bite rate and population density of Dalbergia odorifera leaf eating pests were consistent.There were six key ecological control indexes of aboveground stratification structure.The order of significance was tree height,mixing degree,Shannon index,shrub coverage,Pielou index and litter thickness(P<0.01).The regression prediction model of insect bite rate(Yi1)constructed by six key indicators was as follows:Yi1=0.886-0.364x1-0.379x2-0.208x3+0.107x4-0.101x5-0.031x6;The constructed insect population density(Yi2)prediction model is:Yi2=1.317-0.267x1-0.304x2-0.232x3+0.128x4-0.045x5-0.089x6.The model accuracy test shows that the goodness of fit of the two equation models are high,and the accuracy of the model established with the population density is the best.In the 10 pre-set plots,the prediction accuracy of the regression equation model constructed with the insect bite rate is between 79%-99%,of which the prediction accuracy of 5 plots is more than 90%,the prediction accuracy of the equation model constructed with the population density is between 86%-99%,of which the prediction accuracy of 8 plots is more than 90%.The results show that the two regression models can accurately predict the occurrence degree of the main leaf eating pests in Dalbergia odorifera,and the model can play a positive role in the ecological regulation of leaf eating pests in plantations. |
