A further 1000 were employed in stone quarrying at Graiglwyd and Penmaenmawr. Mining for copper, iron and gold was undertaken during the 18th and 19th centuries, leaving a legacy of mine and mill ruins today. The park's entire coastline is a Special Area of Conservation, which runs from the Llŷn Peninsula down the mid-Wales coast, the latter containing valuable sand dune systems. The park's natural forests are of the mixed deciduous type, the commonest tree being the Welsh oak. Birch, ash, mountain-ash and hazel are also common. The park also contains some large (planted) coniferous forested areas such as Gwydir Forest near Betws-y-Coed, although some areas, once harvested, are now increasingly being allowed to regrow naturally. Northern Snowdonia is the only place in Britain where the Snowdon lily ("Gagea serotina"), an arctic–alpine plant, is found and the only place in the world where the Snowdonia hawkweed "Hieracium snowdoniense" grows. One of the major problems facing the park in recent years has been the growth of "Rhododendron ponticum". This fast-growing invasive species has a tendency to take over and stifle native species. It can form massive towering growths and has a companion fungus that grows on its roots producing toxins that are poisonous to any local flora and fauna for a seven-year period after the "Rhododendron" infestations have been eradicated. As a result, there are a number of desolate landscapes. Rare mammals in the park include otters, polecats, and the feral goat, although the pine marten has not been seen for many years. Rare birds include raven, red-billed chough, peregrine, osprey, merlin and the red kite. The rainbow-coloured Snowdon beetle ("Chrysolina cerealis") is only found in northern Snowdonia. Snowdonia has a particularly high number of protected sites in respect of its diverse ecology; nearly 20% of its total area is protected by UK and European law. Half of that area was set aside by the government under the European Habitats Directive as a Special Area of Conservation.There are a large number of Sites of special scientific interest (or 'SSSIs'), designated both for fauna and flora but also in some cases for geology.