Selective logging is the logging practice of entering a forest and only removing some trees, usually those which are unhealthy or in dense areas. Sometimes the logging is performed on the ground, but to not harm surrounding forest, it is more often done by air using a helicopter. Selective logging has been well-documented to improve forest health and reduce the dangers of wildfire and has been endorsed by the National Forest Service as the better alternative to clear-cutting. It is also supported by the UN. Another advantage is that through the selection of which trees to log, rare species can be saved from the logger's saw.