Arbor Day is a holiday in which individuals and groups are encouraged to plant and care for trees. Arbor Day originated in the United States but is also celebrated by several other countries.

As far back as the Civil War, Americans were concerned that the forests were being destroyed by logging and the conversion of woodland to farms. There was talk of an impending "national famine of wood," and indeed the facts must have seemed discouraging at a time when wood was the chief source of energy. In the late 19th century there was little prospect of a major expansion of prime cropland needed to feed a population that was increasing by more than 20 percent per decade. But the ecological crisis that loomed never came.

Forest acreage stopped declining about 1920 because there was little need for additional farms. In fact, forests in many parts of the Northeast and the South have actually expanded since 1900, as agriculture shifted to the Midwest. The need for new farm acreage diminished partly because the use of crops to feed draft animals declined steeply with the introduction of tractors and other motorized equipment. And the productivity of farms rose as a result of genetically improved strains, increased use of fertilizers and better irrigation.

Forests also recovered as coal and oil replaced fuel wood, and conservation measures begun in the era of President Theodore Roosevelt and his chief of the forest service, Gifford Pinchot, started to take effect. Pollution by pulp and paper mills was cut drastically, and tree planting increased. Although population has grown by 2.5 times in the past 80 years, forests have been able to satisfy the rising demand for lumber, paper and other wood products.