The eastern savannas of the United States covered large portions of the east side of the continent until the early 20th century. These were in a fire ecology of open grassland and forests with low ground cover of herbs and grasses. In the southern pine savanna, each area burned about every 1–4 years; after settlers arrived burning happened about every 1–3 years. In oak–hickory areas, estimates range from 3 to 14 years, although trails were kept open with fire.