Forests screening effect on distribution of traffic noise

Noise is one of the most popular environmental pollution. Long-standing residence in noisy areas can cause discomfort, problems with sleeping, neurosis, etc. Because of moving sources and increasing the number of routs, communicative noise is drudging on the huge areas. The level of noise emitted depends on the number of vehicles, as well as their types, speed and technical condition and also the type of routs pavement. Propagation of acoustic waves in the roadside area is stipulated by sound's source energy as well as characteristics of the emitter. Forest ecotone zones and roadside afforestation constitute a certain ecological filter buffering contaminations generated by traffic. Trees and shrubs growing in the vicinity of routs are able to reflect as well as absorb noise. They can form natural acoustic screen. The paper presents an assessment of the propagation of communicative noise on the forestry areas by analysis of variance. Researchers were carried out in the forest area, urban and park forests. Evaluation of noise propagation was conducted in January and July 2006. The measurements’ intensity of noise was interpreted according to model three-factor linear model as well as two-factor linear model. Measuring points were located in different distances away from the crown road (factor A). Researchers were carried out in winter and vegetation periods (factor C). The results obtained on forest areas were compared with those of nonforest control areas (factor B). For comparison purposes research was also carried out near the polycarbonate acoustic baffle. On the basis of analysis of variance it can be noticed that all null hypothesis of main factors effects are rejected in favour of alternative hypothesis at significance level α=0.01. It means that each factor influences on the level of communicative noise. The carried out research showed that the most important factor which determines noise propagation is plant cover. The equivalent noise levels were similar in both research periods in the afforestations situated in Złotniki, the national road 11 and Poznań, the Umultowska street. It results from the fact that the dominant species in the analysed afforestations was Pinus sylvestris L. The most significant equivalent level value decrease occurred in the 50m wide belt of the pine stand. The equivalent noise levels were similar in both research periods in the afforestations situated in Złotniki, the national road 11 and Poznań, the Umultowska street. It results from the fact that the dominant species in the analysed afforestations was Pinus sylvestris L. The most significant equivalent level value decrease occurred in the 50m wide belt of the pine stand. The approx. 30m wide pine stand reduces noise propagation both in winter and summer to a degree comparable to the polycarbonated acoustic screen. The broad-leaved shrub-belt in the Sołacki Park decreased the equivalent noise level value (by approx. 5 dB) only in the vegetation season.