| The purpose of this paper was to study the noise reduction characteristics of the crowns of single trees.By measuring and calculating the noise attenuation,the noise reduction abilities of the crowns of single trees of different species were measured and analyzed by spectrum analysis.By analogizing various noise reduction materials in noise pollution control engineering,the acoustic characteristics of the structure and its influencing factors,classification and multi-dimensional quantification of the biological structure characteristics of a single plant crown were carried out.The correlation between the noise reduction characteristics of single tree crown and its biological structure was analyzed,and the biological structure characteristics affecting the noise reduction ability and the sensitive frequency band of noise reduction were found out respectively,and the quantitative indicators for screening and evaluating noise reduction plants were developed accordingly.10 species of plants were selected for the experiment,including Acer truncatum,Acer negundo ’Aureum’,Fraxinus chinensis,Ailanthus altissima,Prunus cerasifera ’Atropurpurea’,Sophora japonica,Ginkgo biloba,Platycladus orientalis,Pinus tabulaeformis,and Pinus armandii.The following conclusions are obtained:(1)The noise reduction ability of the whole crown of the 10 tested plant species ranged from 1.13%to 4.28%per meter,and the noise reduction ability of 7 broad-leaved trees was better than that of three coniferous trees.(2)The attenuation ability of the crown of different tree species to the same frequency noise is different,and the noise reduction ability of the crown of the same tree species is also different to the different frequency.The noise reduction ability of the plant crown increases with the increase of the noise frequency.In the low-frequency band,there was no significant difference in the noise reduction ability of plant crown at these eight frequencies.The attenuation effect of conifers on low-frequency noise was stronger than that of broad-leaved trees.Pinus tabulaeformis,Pinus armandii,and Fraxinus chinensis were the most effective species for low-frequency noise attenuation.In the mid-low-frequency band,the difference of tree species caused a significant or extremely significant difference in noise reduction ability of plant crown.Most plants appear in this frequency band noise reduction peak and valley value,most of the peak appears in 200-250 Hz,valley value appears in 315-400 Hz.The tree species with better attenuation effect to low-and medium-frequency noise were Platycladus orientalis,Sohpora japonica,and Ailanthus altissima.In the mid-high-frequency band,the noise reduction ability of different tree species was significantly different to that of plant crown.Besides,the noise reduction ability of other tree species in this frequency band did not fluctuate significantly with the frequency.The tree species with better attenuation effect on mid-high-frequency band noise are Platycladus orientalis,Acer negundo ’Aureum’,and Ailanthus altissima.In the high-frequency band,all of them increased with the increase of noise frequency.The noise reduction ability of plant crown had significant differences between different tree species,and the noise reduction ability of tree crown increased with the increase of noise frequency,and the noise reduction ability of tree crown was significantly different with the increase of noise frequency.The attenuation effect of conifers on high-frequency noise was weaker than that of broad-leaved trees.The best tree species for high-frequency noise attenuation were Acer truncatum,Ailanthus altissima,and Ginkgo biloba.(3)The noise reduction peak frequency of the whole crown of 5 species of plants,including Sophora japonica,Acer negundo ’Aureum’,Platycladus orientalis,Pinus tabulaeformis and Pinus armandii,was significantly higher than the noise reduction peak valley,that is,the noise attenuation at shorter wavelength was higher than that of the whole tree crown.There was no significant difference in noise reduction peak value and valley frequency between tree crowns of Acer truncatum,Ailanthus altissima and Ginkgo biloba While Prunus cerasifera ’Atropurpurea’ and Fraxinus chinesis had significantly higher noise reduction valley frequency than peak frequency,that is,the noise attenuation at longer wavelengths was greater than that of the peak frequency.(4)There was a high correlation between the noise reduction ability of crowns of 7 broad-leaved plants and the quantitative value of different dimensions of crown porosity.Among them,the noise reduction ability of Ginkgo biloba and Acer negundo ’Aureum’was greatly influenced by the crown porosity of three dimensions.The noise reduction ability of crown of Acer truncatum,Prunus cerasifera ’Atropurpurea’ and Ailanthus altissima was affected by one-dimensional and two-dimensional porosity of crown and the leaf structure characteristics were also very significant in the effect of their noise reduction ability of crown.The noise reduction ability of crowns of Fraxinus chinesis and Sophora japonica was most affected by the three-dimensional porosity of crowns,but the former was also influenced by leaf structure,while the latter was significantly affected by branch structure.(5)There were similarities and differences between the most related biological structural characteristics of the sensitive frequency band of noise reduction in the crown of 10 species of tested plants,and the total pore length of the crown was the most relevant to those of Ailanthus altissima,Acer truncatum,and Sophora japonica.Leaf structure was the most related to Fraxinus chinensis and Acer negundo ’Aureum’.Both leaf and branch structures were most related to the sensitive frequency band of noise reduction of Prunus cerasifera ’Atropurpurea’,Ginkgo biloba and Platycladus orientalis.The most related biological structure characteristic with Pinus tabulaeformis was branch diameter,and crown width was the most correlated with Pinus armandii. |
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