The negative impacts of roads on biological integrity include habitat destruction and fragmentation, edge effects, exotic species invasions, pollution, and overhunting. The most obvious effect of roads is the increased access they provide for humans. Forest road networks open areas of normally inaccessible forest to human activities that may threaten biodiversity, watersheds, and aquatic habitats. The most critical implications on the Lincoln NF are the introduction and spread of noxious weeds and the increased access roads provide to motorized vehicles. Augmented motorized access leads to greater erosion and sedimentation as well as changes in wildfire frequency and seasonality.
Roads also have consequences upon hydrology and aquatic habitats.
Erosion and sedimentation from roads is arguably the most damaging effect. The Lincoln NF is plagued with noxious weeds. At least 11 non-native, invasive weed species have contaminated 4,291 acres primarily along roads and trails. Roads closed or scheduled for closure on the Sacramento Ranger District of the Lincoln National Forest were surveyed for effectiveness, degree of vegetation, and degree of erosion. Where roads are open to vehicular traffic, results indicate there is a lesser degree of vegetation as well as a greater degree of erosion resulting in conditions favorable for noxious weed colonization.