Historically, fire has been a frequent and major ecological factor in North America. In the conterminous United States during the preindustrial period (1500- 1800), an average of 145 million acres burned annually. Today only 14 million acres (federal and non-federal) are burned annually by wildland fire from all ignition sources. Land use changes such as agriculture and urbanization are responsible for 50 percent of this 10-fold decrease. Land management actions including land fragmentation and fire suppression are responsible for the remaining 50 percent.
This decrease in wildland fire has been a destabilizing influence in many fire- adapted ecosystems such as ponderosa pine, lodgepole pine, pinyon/juniper woodlands, southern pinelands, whitebark pine, oak savanna, pitch pine, aspen, and tallgrass prairie. Fuels increased and understory vegetation became more dense. As a result, those wildland fires that did occur were larger and more severe than historical fires. Eliminating fire also affected individual plant species. For example, Hessl and Spackman (1995) found that, of the 146 threatened, endangered, and rare plant species found in the conterminous U. S. for which there is conclusive information on fire effects, 135 species benefit from wildland fire or are found in fire-adapted ecosystems.
Source: U.S. government