In the early part of the 20th century and especially the period during and after World War II and the Korean War, much of the existing Korean forests were cut down, which led to problems with flooding and soil erosion. Combination of reforestation efforts (e.g. Arbor day was celebrated as a national holiday starting in 1949) and policies designed to reduce the use of firewood as a source of energy (e.g. restriction of inflow of firewood into Seoul and other major cities starting in 1958) helped to spark a recovery in the 1950s. Comprehensive reforestation programs starting in the 1970s and continuing into the late 1990s aided in an acceleration of forest volume increase, and the forest cover reached a peak of 65% of national land area in 1980 as opposed to a low of 35% in 1955.