Pine rocklands (also called pinelands) are found on uneven limestone substrates that contain pinnacles and solution holes. There are three primary locations of pine rocklands: the Miami Ridge, which runs from Miami into Long Pine Key near the main entrance of Everglades National Park; the lower Florida Keys; and the Big Cypress Swamp.[49] The most significant feature of the pine rockland ecosystem is the South Florida slash pine (Pinus elliotti var densa; also called Dade County pine) that reaches a height of 22 feet (6.7 m). Pine rockland communities require fire for maintenance; they have adapted to promote and resist fire at the same time.[50] These communities are located in the highest part of the Everglades with little to no hydroperiod, although some floors may have flooded solution holes or puddles for a few months at a time. The sandy floor of the pine rocklands is covered with dry pine needles that are highly flammable. South Florida slash pines are insulated by their bark to protect them from heat. Fire eliminates competing vegetation on the forest floor, and opens pine cones to germinate seeds.[51] A period without significant fire can turn pineland into hardwood hammock as larger trees overtake the slash pines.[52] The understory shrubs in pine rocklands include fire-resistant species like saw palmetto (Serenoa repens), cabbage palm (Sabal palmetto), and West Indian lilac (Tetrazygia bicolor). The most diverse group of plants in the pine community are herbs, of which two dozen species exist. These plants contain tubers and other mechanisms allowing for quick sprouts after charring.[53]