Biodiversity conservation has become a central issue for the promotion of sustainable development.The reduction of habitat area and connectivity is currently considered a major threat to biodiversity conservation.Road networks contribute significantly to a decrease in both the quantity and the quality of such habitat.Characterizing the impact of road networks on biodiversity at variable scales is important for understanding threats to species conservation at multiple levels of management.This research focuses on the impacts of road networks on habitat loss,connectivity loss and biodiversity change in a region of the Lancang River Valley in Yunnan province.Our findings indicated that (1) from 1997 to 2007,forest habitat larger than 25 ha decreased in area by 18.3% due to fragmentation; (2) relative forest biomass represented by NDVI decreased by 66.0% due to a 98% conversion of patches from forest to shrubs; and (3) connectivity loss was 91.3% within the road-effect zones.We conclude that road network expansion resulted in habitat fragmentation and degradation and landscape connectivity loss.Forest species under the most severe influence of the road networks were those relying on large forest patches within distances ranging from 360 m to 720 m to roads,altitudes from 2025 m to 2300m,and those in the southern and western part of the study area.The 12-kin dispersal movement of those species was disturbed most seriously.