Early explorers in the Sierra Nevada described the groves of big-trees, Sequoia gigantea (also called Sierra redwood, or giant sequoia) as essentially clean, open, and parklike. The frequent ground fires of primitive times, started by lightning and by Indians, kept the forest floor relatively clean. Today, as a result of fire suppression, many of the groves have a dense understory of shade-tolerant trees, mainly white fir and incense-cedar. The understory of crowded trees has come to be of considerable concern to people interested in park vegetation maintenance because the small trees add to the fire hazard and partially block out the views of the giants.