Aldo Leopold, a conservationist known for his essays in his Sand County Almanac, defended the worth of wildlife management in his lifetime. His work included the first textbook on wildlife management, "Game Management," and his concepts of managing populations, habitats, and interrelationships as a whole, sustainable population densities, ethical hunting practices and habitat stewardship, and the integration of forestry, agriculture, and wildlife management practices for the best outcome. Gifford Pinchot, the first chief of the National Forest Service, also understood the importance of efficiency in resource use and conservation. Today, Colorado Parks and Wildlife is funded entirely by the sale of licenses, permits, and federal grants.