From the beginning of the colonial period, much of Guanajato's environment suffered greatly from the mining techniques and intensive agriculture the Spanish introduced. The process has been ongoing since then to modern times. Before the conquest, the state was covered in forests, but mining requires large amounts of fuel to process minerals, so they were cut down for fuel and construction projects. Agriculture leached nutrients from the soil, caused erosion, and introduced plants, animals and diseases that have had a large impact. Today, the state contains 21 protected areas that extend over 63,611 hectares in 26 municipalities. These include Sierra de Lobos, Siete Luminarias, the Silva Dam, Megaparque de Dolores Hidalgo, Cuenca de la Esperanza, Las Fuentes, Peña Alta, Pinal de Zamorano, Parque Metropolitano, La Joya Crater, Yuriria Lake, Las Musas, Culiacán and La Gavia Mountains, Sierra de los Agustinos, Cerro de Cubilete, Cerro de Amoles, La Purisima Dam, Arandas Mountain, La Soledad Dam, and the upper basin of the Temascatío River. Another protected area is the federal Biosphere Reserve of La Sierra Gorda. In Guanajuato, it extends over 236,882 hectares and contains 182 bird species, 42 mammal species and 84 plant species, including two recently discovered ones, Beaucamea compacta and Calibanus glassianus. The park contains a number of species in danger of extinction, including the black bear and the puma. The climate is semiarid with variations in temperature due to altitude changes, but most of the area is covered in tropical forest in which many plants lose leaves during the dry season from November to May.