The response of native plant species to mechanical fuel reduction treatments

Since 2000, federal land management agencies have treated over 6 million hectares (15 million acres) to reduce hazardous fuels across the United States. These projects are designed to reduce fire hazard in the wildland-urban interface and to improve the effectiveness of fire suppression activities. We studied fuel breaks across California, U.S.A., to evaluate how they affect plant species diversity and composition. We found that native plant diversity was significantly higher on fuel breaks than in adjacent wildland areas. Almost 20% of the native plant species observed in our plots were found only on fuel breaks. Fuel breaks were characterized by higher numbers of native annual species than adjacent wildland areas. Some species of native perennial grasses, forbs, and shrubs were also more commonly found on fuel breaks than adjacent wildlands. In fire-suppressed forests in California, unnaturally long fire-free periods may have decreased native plant species diversity, particularly in the herbaceous understory. We found that fuel reduction treatments apparently produce the kind of open, periodically-disturbed habitats, historically maintained by fire, that some native species prefer. In order to maintain native plant diversity, managers must recognize the natural role of disturbance in Californian ecosystems. However, efforts to restore natural disturbance regimes must include measures to prevent concurrent invasion and spread of nonnative species.