The impact of trails and roads on the fungal pathogens of Pringle manzanita (Arctostaphylos pringlei)

Human disturbances, such as roads and trails, are being increasingly recognized as drivers of ecological change, particularly in sensitive plant communities. In chaparral ecosystems of southern California, these disturbances may facilitate the introduction and spread of infectious fungi by altering soil conditions and enabling human-mediated dispersal. To investigate this, we examined the impact of disturbance proximity on leaf fungal infections of Arctostaphylos pringlei (Pringle manzanita), a native shrub in the San Jacinto Mountains in southern California. We sampled 80 individual manzanitas across three sites varying in exposure to roads and trails, quantifying two distinct fungal infections, herbivory, and new bud growth. Black fungal infections were significantly more prevalent near trails and roads, and were associated with reduced bud growth, suggesting a pathogenic impact facilitated by disturbance. In contrast, red fungal infections varied among sites, but did not correlate with distance to disturbance or plant health. Herbivory showed no relationship to either fungal infection type. These findings indicate that black fungal pathogens may be spread by human disturbance vectors, such as soil movement and edge creation, while red fungi may be less virulent. Conscientious trail planning and habitat buffer implementation could help reduce pathogen introduction into native chaparral flora.