and . Ramsar sites The three designated Ramsar sites are the Dyfi Biosphere (Cors Fochno and Dyfi), Cwm Idwal and Llyn Tegid (Bala Lake). Economy The area's economy was traditionally centred upon farming and from the early 19th century increasingly on mining and quarrying. Tourism has become an increasingly significant part of Snowdonia's economy during the 20th and 21st centuries. Hill farming The extensive farming of sheep remains central to Snowdonia's farming economy. Forestry Significant sections of the park were afforested during the 20th century for timber production. Major conifer plantations include Dyfi Forest, Coed y Brenin Forest between Dolgellau and Trawsfynydd, Penllyn Forest south of Bala, Beddgelert Forest and Gwydyr (or Gwydir) Forest near Betws-y-Coed which is managed as a forest park by Natural Resources Wales. Slate industry The region was once the most important producer of slate in the world. Some production continues but at a much reduced level from its peak. The park boundaries are drawn such that much of the landscape affected by slate quarrying and mining lies immediately outside of the designated area. Energy production Construction of a nuclear power station beside Llyn Trawsfynydd began in 1959 with the first power produced in 1965. The site was operational until 1991 though it continues as an employer during its decommissioning phase. Pumped storage hydroelectric schemes are in operation at Llanberis and Ffestiniog. Tourism Research indicates that there were 3.67 million visitors to Snowdonia National Park in 2013, with approximately 9.74 million tourist days spent in the park during that year. Total tourist expenditure was £433.6 million in 2013. Hiking Many of the hikers in the area concentrate on Snowdon itself. It is regarded as a fine mountain, but at times gets very crowded; in addition the Snowdon Mountain Railway runs to the summit. The other high mountains with their boulder-strewn summits as well as , one of the few mountains in the UK south of Scotland whose ascent needs hands as well as feet are also very popular. However, there are also some spectacular walks in Snowdonia on the lower mountains, and they tend to be relatively unfrequented. Among hikers' favourites are Y Garn (east of Llanberis) along the ridge to Elidir Fawr; Mynydd Tal-y-Mignedd (west of Snowdon) along the Nantlle Ridge to Mynydd Drws-y-Coed; Moelwyn Mawr (west of Blaenau Ffestiniog); and Pen Llithrig y Wrach north of Capel Curig. Further south are Y Llethr in