Article: Despite the fact that humans have occupied the territory of Portugal for thousands of years, something still remains of the original vegetation. In Geres both deciduous and coniferous forests can be found, an extremely rare worldwide mature mediterranean forest remain in some parts of the Arrabida mountain and a subtropical laurissilva forest, dating back to the Tertiary period, covers its largest continuous area in the world in the Madeira main island. Due to the human population decrease and rural exodus, Pyrenean oak and other local native trees are colonizing many abandoned areas. Boar, Iberian red deer, roe deer, Iberian wild goat, for example, are reported to be expanding greatly, during the last decades. Boars were found recently roaming at night inside large urban areas, like in Setubal. Protected areas of Portugal include one national park (Portuguese: Parque Nacional), 12 natural parks (Portuguese: Parque Natural), nine natural reserves (Portuguese: Reserva Natural), five natural monuments (Portuguese: Monumento Natural), and seven protected landscapes (Portuguese: Paisagem Protegida), which include the Parque Nacional da Peneda-Geres, the Parque Natural da Serra da Estrela and the Paul d'Arzila.

Now answer this question: To what period does the laurissilva forest date back to?
the Tertiary period