by predator pressure. In the absence of functional communities of large migratory herds of herbivorous megafauna and attendant predators, overuse of fire to maintain grassland ecosystems may lead to excessive oxidation, loss of carbon, and desertification in susceptible climates. Some grassland ecosystems respond poorly to fire. North American grasslands In North America fire-adapted invasive grasses such as Bromus tectorum contribute to increased fire frequency which exerts selective pressure against native species. This is a concern for grasslands in the Western United States. In less arid grassland presettlement fires worked in concert with grazing to create a healthy grassland ecosystem as indicated by the accumulation of soil organic matter significantly altered by fire. The tallgrass prairie ecosystem in the Flint Hills of eastern Kansas and Oklahoma is responding positively to the current use of fire in combination with grazing. South African savanna In the savanna of South Africa, recently burned areas have new growth that provides palatable and nutritious forage compared to older, tougher grasses. This new forage attracts large herbivores from areas of unburned and grazed grassland that has been kept short by constant grazing. On these unburned "lawns", only those plant species adapted to heavy grazing are able to persist; but the distraction provided by the newly burned areas allows grazing-intolerant grasses to grow back into the lawns that have been temporarily abandoned, so allowing these species to persist within that ecosystem. Longleaf pine savannas Much of the southeastern United States was once open longleaf pine forest with a rich understory of grasses, sedges, carnivorous plants and orchids. These ecosystems had the highest fire frequency of any habitat, once per decade or less. Without fire, deciduous forest trees invade, and their shade eliminates both the pines and the understory. Some of the typical plants associated with fire include yellow pitcher plant and rose pogonia. The abundance and diversity of such plants is closely related to fire frequency. Rare animals such as gopher tortoises and indigo snakes also depend upon these open grasslands and flatwoods. Hence, the restoration of fire is a priority to maintain species composition and biological diversity. Fire in wetlands Many kinds of wetlands are also influenced by fire. This usually occurs during periods of drought. In landscapes with peat soils, such as bogs, the peat substrate itself may burn, leaving holes that refill with water as new ponds. Fires that are less intense will remove accumulated