The woods that meet the National Standard in the United States are primarily hardwoods. Hardwoods are derived from deciduous trees, which are characterized by their broad leaves that change color and drop annually. These woods are highly sought after for their durability, strength, and aesthetic appeal. The National Hardwood Lumber Association (NHLA) sets the standards for hardwood lumber, ensuring that it meets specific criteria for quality, size, and grade.

According to the NHLA, the following hardwoods are commonly recognized as meeting the National Standard:

1. Oak: Oak is one of the most popular hardwoods in the United States. It is known for its strength, durability, and beautiful grain patterns. Oak is used in a wide range of applications, including furniture, flooring, and construction.

2. Maple: Maple is another popular hardwood, prized for its fine grain and light color. It is commonly used in sports equipment, such as baseball bats and bowling pins, as well as in furniture and flooring.

3. Cherry: Cherry wood is highly valued for its rich red color and smooth texture. It is often used in high-end furniture and cabinetry.

4. Ash: Ash is a versatile hardwood with a straight grain and a light color. It is used in a variety of applications, including furniture, flooring, and sports equipment.

5. Walnut: Walnut is known for its dark, rich color and straight grain. It is used in high-end furniture, cabinetry, and flooring.

The reason these woods meet the National Standard is due to their consistent quality, availability, and performance. The NHLA has stringent grading systems in place to ensure that each piece of hardwood lumber meets the required specifications. This includes dimensions, moisture content, and visual defects. For example, the NHLA's grading system for oak lumber includes four grades: Select, Common, Better, and Standard. Each grade has specific requirements for the number and size of knots, wane, and other defects.

Data from the NHLA indicates that hardwoods meeting the National Standard are widely used in the construction and manufacturing industries. In 2020, the U.S. hardwood lumber production was approximately 3.5 billion board feet, with oak, maple, and ash being the most popular species. This demand is driven by the woods' ability to withstand heavy use and maintain their appearance over time.

In conclusion, hardwoods such as oak, maple, cherry, ash, and walnut meet the National Standard in the United States due to their consistent quality, availability, and performance. The NHLA's grading system ensures that these woods meet specific criteria for quality, size, and grade, making them suitable for a wide range of applications.