Despite broad recognition that forest machinery access systems impact plant diversity, previous studies have largely focused on skid trails. As a consequence, how tractor trails (dead-end single-use trails) influence plant diversity is poorly understood. In particular, knowledge is lacking on whether fine-scale understory diversity is better indicated by tractor-trail disturbance or by the environment. We investigated the relative importance of tractor-trail disturbance conditions and soil characteristics, as well as their effects on ground floral diversity in four oak forest types (a high forest and three coppicewith-standard forests) in the northern half of France. Subplots representing five types of disturbance conditions were placed on both recent (