北京市3种配置模式绿化带降噪效果的空间变化规律

为明确不同配置模式绿化带对噪声衰减效果的空间变化规律,以北京市的刺槐(Robinia pseudoacacia Linn.)纯林(代表阔叶纯林)、刺槐-小花溲疏(Deutzia parviflora Bunge)混交林(代表阔叶混交林)和侧柏〔Platycladus orientalis(Linn.)Franco〕-圆柏〔Sabina chinensis(Linn.)Ant.〕混交林(代表针叶混交林)3类绿化带为研究对象,设置不同高度、距噪声源不同水平距离和不同噪声频率3组变量,对3类绿化带的降噪值进行比较分析.结果表明:3类绿化带的降噪效果由高至低依次为针叶混交林、阔叶混交林、阔叶纯林.在不同高度和距噪声源不同水平距离处,3类绿化带对不同频率噪声有各自的降噪优势;其中,在高度0.5和1.5 m处,阔叶混交林对250~1000 Hz噪声的衰减效果总体上优于阔叶纯林,而阔叶纯林对4000 Hz的噪声衰减效果却优于阔叶混交林,并且,针叶混交林对250、500、1000和8000 Hz噪声的衰减效果总体上优于阔叶纯林;整体上看,在距噪声源水平距离超过10 m处,3类绿化带对125~1000 Hz噪声的衰减效果最优.相关性分析结果表明:3类绿化带的降噪率与噪声频率呈负相关,与距噪声源水平距离和单位面积三维绿量总体上呈正相关.其中,在高度0.5、1.5和2.5 m处,3类绿化带的降噪率与噪声频率和距噪声源水平距离总体上显著相关;而在高度0.5和1.5 m处,3类绿化带的降噪率与单位面积三维绿量总体上显著相关.从3类绿化带的降噪规律看,在距噪声源水平距离相同的位置,高度越低,绿化带的降噪值越大,其中高度2.5 m以下绿化带的降噪值均较大;在相同高度上,距噪声源水平距离10和15 m处3类绿化带的降噪值总体上较大,但在距噪声源水平距离15和20 m处针叶混交林的降噪值明显大于其他2类绿化带.根据上述研究结果,建议绿化带宽度应在10 m以上,在配置绿化带时,应选择分枝点低、枝叶密度大的树种,且在不影响树木生长的条件下尽量密植并适度配置灌木.

Spatial variation rule of noise reduction effect of three configuration modes of greenbelts in Beijing City

In order to clarify the spatial variation rule of attenuation effect of different configuration modes of greenbelts on noise, taking three types of greenbelts including Robinia pseudoacacia Linn. pure forest ( representing broad-leaved pure forest ) , R. pseudoacacia-Deutzia parviflora Bunge mixed forest (representing broad-leaved mixed forest) and Platycladus orientalis ( Linn.) Franco-Sabina chinensis (Linn.) Ant. mixed forest (representing coniferous mixed forest) in Beijing City as research objects, three groups of variables of different heights, different horizontal distances from noise source and different noise frequencies were set up to compare and analyse the noise reduction value of three types of greenbelts. The results show that the noise reduction effect of three types of greenbelts from high to low is coniferous mixed forest, broad-leaved mixed forest, broad-leaved pure forest. At different heights and different horizontal distances from noise source, there are respective noise reduction advantages for different frequency noises in three types of greenbelts. In which, at height of 0. 5 and 1. 5 m, the attenuation effect of broad-leaved mixed forest on noise of 250-1000 Hz is generally better than that of broad-leaved pure forest, while that of broad-leaved pure forest on noise of 4000 Hz is better than that of broad-leaved mixed forest, and that of coniferous mixed forest on noise of 250, 500, 1000 and 8000 Hz is generally better than that of broad-leaved pure forest. On the whole, at horizontal distance from noise source more than 10 m, attenuation effect of three types of greenbelts on noise of 125-1000 Hz is the best. The correlation analysis results show that there is a negative correlation of noise reduction rate of three types of greenbelts with noise frequency, and there are generally positive correlations of noise reduction rate with horizontal distance from noise source and living vegetation volume per unit area. In which, in general, at height of 0. 5, 1. 5 and 2. 5 m, there are significant correlations of noise reduction rate of three types of greenbelts with noise frequency and horizontal distance from noise source, while at height of 0. 5 and 1. 5 m, there is a significant correlation of noise reduction rate of three types of greenbelts with living vegetation volume per unit area. From view of noise reduction rule of three types of greenbelts, at the same horizontal distance from noise source, the lower the height, the larger the noise reduction value of greenbelts, in which, noise reduction value of greenbelts at height lower than 2. 5 m is large. In general, at the same height, noise reduction value of three types of greenbelts at horizontal distance from noise source of 10 and 15 m is large, but that of coniferous mixed forest at horizontal distance from noise source of 15 and 20 m is obviously larger than that of other two types of greenbelts. According to above research results, it is suggested that width of greenbelt should be more than 10 m. When configuring greenbelt, it should select tree species with low branch point and large branch and leaf density, and try to close planting with suitable shrubs under the condition of not affecting growth of trees.