Roadside noise barriers as biodiversity refuges under pressure: the role of particulate matter in shaping invertebrate communities

Road transportation emits both gaseous and solid air contaminants, along with significant noise pollution. To mitigate the noise, acoustic walls and berms are constructed along roads. When covered with vegetation, these structures can also reduce particulate matter (PM) pollution and provide habitats for invertebrates in environments fragmented by road infrastructure. This study aimed to measure the effectiveness of vegetated acoustic berms (covered with meadow vegetation, Rosa rugosa, or Spiraea japonica) and walls (Parthenocissus quinquefolia or Vitis riparia) created in accumulation of PM and providing shelter for invertebrates along a busy motorway. A combination of field and laboratory analyses, including plant and invertebrate sampling and air quality measurements, was used to assess the links between PM accumulation on vegetation and invertebrate diversity indices (S, H′, D′, J', Chao1, and BP) on both sides (sidewalk vs. roadside) of a given barrier. Results indicated that all barrier types improved air quality on sidewalks compared to traffic-exposed roadsides. Despite the highest total PM accumulation, berms with meadow vegetation and R. rugosa supported the greatest abundance and diversity of invertebrates (210 species combined). The roadsides were characterized by the lowest diversity indices and the highest prevalence of common taxa, indicating a significant role of PM in shaping invertebrate communities, especially the flying insects. This was further supported by Pearson's correlations between total PM on plants and ecological indices values. The findings suggest that ecosystem services of noise reduction, PM biofiltration, and invertebrate diversity support are best achieved with earth berms planted with meadow vegetation and R. rugosa shrubs.