practices conservation of resources, which ensures a sustainable flow of some raw materials from the forest, such as lumber for construction purposes and wood pulp for paper products. The forest averages an annual harvest of 4.5 million board-feet of timber for the purposes of commercial log home construction and another 2.5 million board-feet of wood collection from dead and down trees that are used for firewood and poles. Additionally, low-scale mineral extraction and oil and gas exploration and recovery are also conducted, though in Shoshone National Forest this has become less common due to a consensus to protect the natural surroundings. Only of oil and gas leases were filed as of 2013. More common than logging and mining are the lease options that are offered to ranchers to allow them to graze cattle and sheep. The U.S. Forest Service provides guidelines and enforces environmental regulations to ensure that resources are not overexploited and that necessary commodities are available for future generations, though conservation groups have voiced concerns over the management practices of the leasing program and especially cattle overgrazing problems. Leases for sheep grazing have declined considerably since the 1940s while cattle grazing has remained relatively constant. Natural resources Flora Shoshone National Forest is an integral part of the Greater Yellowstone Ecosystem, which has 1,700 documented species of plants. Since the elevation of the land in the forest ranges from , which is more than , the forest has a wide variety of ecosystems. Lower elevations often have sagebrush and grass-dominated vegetation types, while forested areas are dominated by various combinations of tree and shrub species. These include lodgepole pine, which along with Rocky Mountain juniper, and quaking aspen are found at elevations up to . At higher elevations subalpine fir, Engelmann spruce, whitebark pine and limber pine, are common, each occurring up to timberline. The region above timberline makes up 25 percent of the total acreage of the forest and of that 13 percent is listed as just either barren, rock or ice. The types of plant species is highly dependent on the amount of water available, and trees are more commonly found on higher slopes due to the longer lasting snowfall which keeps the soil moister for a longer time into the summer months. Along lower elevation riparian corridors, cottonwoods and willows are typically dominant. Numerous plant species are endemic to the region including some that are rare.