Study On Noise Reduction Characteristics And Impact Factors Of 10 Garden Trees Before And After Defoliation

The aim of this paper was to study the noise reduction characteristics of different individual plants before and after defoliation and its influencing factors.By measuring the noise attenuation effects of different frequency bands,different sound pressure levels and different distances before and after defoliation,the noise reduction characteristics of each plant were explored.Then,the morphological and structural characteristics of a single plant are further quantified,and the correlation analysis between the morphological and structural characteristics and the noise reduction characteristics is carried out to explore the influence of the plant’s own morphological and structural characteristics on the noise reduction characteristics.Through the study on the noise reduction characteristics of plants before and after defoliation and its influencing factors,it provides some scientific basis for the selection and application of noise reduction plants in gardens.In this study,the noise reduction characteristics and morphological structures of four deciduous shrubs(Clerodendrum trichotomum,Weigela florida,Viburnum opulus var.calvescens,Cotoneaster multiflorus)and six deciduous trees(Malus halliana,Crataegus pinnatifida,Prunus cerasifera f.Atropurpurea,Cornus officinalis,Tamarix chinensis,Acer truncatum)before and after defoliation were measured and analyzed,and the following conclusions were reached:(1)The noise reduction effects of the 10 species before defoliation are significantly better than that after defoliation,indicating that leaf is the key factor of noise reduction.According to the average noise reduction rate and average noise reduction ability of the plants before defoliation,the noise reduction effects of the 10 test tree species can be clearly divided into three categories:the noise reduction effects of Cornus officinalis,Acer truncatum and Weigela florida before defoliation are better,the noise reduction effects of Prunus cerasifera f.Atropurpurea,Clerodendrum trichotomum,Viburnum opulus var.calvescens,Tamarix chinensis,Crataegus pinnatifida and Malus halliana are moderate,the noise reduction effect of Cotoneaster multiflorus is poor.(2)Different plants have different attenuating effects on noise with different intensity.Malus halliana,Crataegus pinnatifida,Cornus officinalis and Viburnum opulus var.calvescens have better noise reduction effect on low-intensity sound source(80-90 d B),but poor noise reduction effect on high-intensity sound source(90-100 d B).Weigela florida,Prunus cerasifera f.Atropurpurea,Cotoneaster multiflorus,Tamarix chinensis and Acer truncatum have better noise reduction effect on high-intensity sound source,but poor noise reduction effect on low-intensity sound source.While,there is no significant difference in noise reduction effect between different sound sources in Clerodendrum trichotomum.(3)The distance of the plant from the sound source has great difference on the effect of noise reduction.Malus halliana,Prunus cerasifera f.Atropurpurea,Cornus officinalis,Viburnum opulus var.calvescens and Tamarix chinensis have poor noise reduction effect on the near source(1-2m),but better noise reduction effect on the far source(2-3m).Crataegus pinnatifida,Clerodendrum trichotomum and Cotoneaster multiflorus have poor noise reduction effect on the far source,but better noise reduction effect on the near source.While,there was no significant difference in the noise reduction effect between different distance sources in Weigela florida and Acer truncatum.(4)In the measured plants,most of the plants have better attenuation effect on the noise of high frequency band(more than 5000Hz)than on the noise of medium and low frequency band(less than5000Hz).However,it is not that the higher the frequency,the better the noise reduction effect is,but that it begins to decline around 12500 Hz.(5)Not all plants have sensitive frequency band for noise reduction.Crataegus pinnatifida,Cotoneaster multiflorus and Tamarix chinensis have no sensitive frequency band for noise reduction.The peak value of noise reduction(i.e.,the frequency with the maximum noise reduction)of Malus halliana,Clerodendrum trichotomum,Weigela florida,Prunus cerasifera f.Atropurpurea,Cornus officinalis and Acer truncatum all appeared in the high frequency band(5000-2000Hz),and the valley value of noise reduction(i.e.,the frequency with the minimum noise reduction)all appeared in the middle frequency band(150-5000Hz),especially in the middle-high frequency band(500-5000Hz).The peak noise reduction value of Viburnum opulus var.calvescens also appeared in the high frequency band,while the noise reduction valley value appeared in the low frequency band(20-150Hz).(6)According to the bivariate correlation analysis,among the major morphological and structural factors affecting the noise reduction effect of pre-deciduous plants,the canopy surface texture and leaf area density are positively correlated,while the canopy facade area,canopy width and canopy porosity are negatively correlated.Among the main morphological and structural factors affecting the noise reduction effect of deciduous plants,the ground diameter and plant height are positively correlated,while the canopy porosity and canopy facade light transmittance are negatively correlated.(7)Among the major morphological and structural factors affecting the peak frequency of plant noise reduction,the leaf area density is positively correlated,while the canopy width and canopy elevation area are negatively correlated.The main morphological and structural factor affecting the frequency of denoising valley value of plants is the angle between first-order branches,which was positively correlated.It can be seen that the main morphological structures affecting noise attenuation in the high frequency band are leaf area density,canopy width and canopy elevation area,while the main morphological structure affecting noise attenuation in the middle and low frequency band is the Angle between branches of the first order.