The impacts of road and walking trails upon adjacent vegetation: effects of road building materials on species composition in a nutrient poor environment

Roads represent an important landscape element affecting both biotic and abiotic components. Alteration of soil properties along roads (addition of nutrients) is assumed to have a great impact on vegetation structure especially in nutrient poor ecosystems. Existing studies focus mainly on road dust. In our study we assessed the overall effects of roads upon adjacent alpine tundra vegetation and soils in Krkonoše Mts, Czech Republic. Our aims were to (1) reconstruct the road-related changes using aerial data and GPS mapping to study colonization of roadside plant species; (2) assess the road effects on physical-chemical soil properties and vegetation composition along transects; and (3) propose conservation measures to stop further damage. Changes were reconstructed from historical multispectral aerial photography (1986 to 1997), measured by GPS device (1997, 2004), and accompanied by detailed soil (1998, 2000 and 2001) and vegetation (2000 and 2004) surveys along transects. Along alkaline roads, fast and profound shifts in physical-chemical soil properties (pH increased from 3.9 up to 7.6, base saturation from 9-30% up to 100%), and species composition were recorded. The roadside vegetation doubled in area during the studied decade. Stress-tolerant tundra species were replaced by meso- to nitrophilous species and species preferring man-made habitats. The intensity of changes depended significantly on the type of road material and the position relative to the road (slope position, distance from the road). Our findings support the assumption that alkaline gravel is the main cause of changes along roads in the area, and indicate the leading role of water transport in the soil and consequent vegetation alteration. To prevent the further damage we recommended replacement of alkaline gravel by granite, even though expensive and technically complicated. Based on our recommendations, the National Park authorities started to reconstruct the trails, although recovery is expected to be slow.