Arbor Day, now observed throughout the US, originated in Nebraska in 1872 as a way of encouraging tree planting in the sparsely forested state. Forestland occupies 947,000 acres (383,000 hectares), or 2% of all Nebraska. Ash, boxelder, hackberry, cottonwood, honey locust, red and bur oaks, walnut, elm, and willow trees are common to eastern and central Nebraska, while ponderosa pine, cottonwood, eastern red cedar, and Rocky Mountain juniper prevail in the west. The state's two national forests—Nebraska and Samuel R. McKelvie—are actually primarily grassland and are managed for livestock grazing. In 1999, the National Forest Service maintained 257,468 acres (104,197 hectares) of forestland.