Although there is no clear definition of the subtropics, this term can refer to the areas of the world that are free of frost, extending from above the 23° North (Tropic of Cancer) and below 23° South of the Equator (Tropic of Capricorn), which roughly reaches to around 35° of latitude in both hemispheres. But these boundaries are not very rigid and there are areas inside the tropics, especially at altitude, which may be considered subtropical. In addition, there are areas at higher latitude, particularly at sea level and with insular climates, which may exhibit climatic conditions that are similar to those of the tropics. This is the reason why some consider that the tropics can be extended to 30° North and South of the Equator (Nakasone and Paull, 1988).