to three terrestrial ecoregions: Central Korean deciduous forests, Manchurian mixed forests, and Southern Korea evergreen forests. South Korea's terrain is mostly mountainous, most of which is not arable. Lowlands, located primarily in the west and southeast, make up only 30% of the total land area. About three thousand islands, mostly small and uninhabited, lie off the western and southern coasts of South Korea. Jeju-do is about off the southern coast of South Korea. It is the country's largest island, with an area of . Jeju is also the site of South Korea's highest point: Hallasan, an extinct volcano, reaches above sea level. The easternmost islands of South Korea include Ulleungdo and Liancourt Rocks (Dokdo/Takeshima), while Marado and Socotra Rock are the southernmost islands of South Korea. South Korea has 20 national parks and popular nature places like the Boseong Tea Fields, Suncheon Bay Ecological Park, and the first national park of Jirisan. Climate South Korea tends to have a humid continental climate and a humid subtropical climate, and is affected by the East Asian monsoon, with precipitation heavier in summer during a short rainy season called jangma (장마), which begins end of June through the end of July. Winters can be extremely cold with the minimum temperature dropping below in the inland region of the country: in Seoul, the average January temperature range is , and the average August temperature range is . Winter temperatures are higher along the southern coast and considerably lower in the mountainous interior. Summer can be uncomfortably hot and humid, with temperatures exceeding in most parts of the country. South Korea has four distinct seasons; spring, summer, autumn and winter. Spring usually lasts from late March to early May, summer from mid-May to early September, autumn from mid-September to early November, and winter from mid-November to mid-March. Rainfall is concentrated in the summer months of June through September. The southern coast is subject to late summer typhoons that bring strong winds, heavy rains and sometimes floods. The average annual precipitation varies from in Seoul to in Busan. Environment During the first 20 years of South Korea's growth surge, little effort was made to preserve the environment. Unchecked industrialization and urban development have resulted in deforestation and the ongoing destruction of wetlands such as the Songdo Tidal Flat. However, there have been recent efforts to balance these problems, including a government run five-year green growth project