There are approximately 500 species of oaks worldwide, with around 90 species growing in the United States. Oak trees reach maturity at 75 years and have an average lifespan of 150-250 years, although the oldest oak trees are over 1,000 years old. While oak trees are typically considered an "average" height tree, some can grow to remarkable heights and widths for their species. For example, one of the largest oak trees ever recorded, the Angel Oak of Johns Island, South Carolina, stands at 65ft tall with a trunk circumference of 28ft.
Depending on their species, oak trees are between 20 and 40 years old when they produce their first acorns. A fully grown oak tree can produce anywhere between 2,000 and 10,000 acorns per year, depending on its species and size. However, for every 10,000 acorns dropped by a single tree, only one will grow into another fully grown oak tree.
Oaks play an essential role in the ecosystem, providing food and habitat for many animals. No other genus of plants supports as many species as oaks. Due to their foundational role in local food webs, oak trees are known as keystone species. Recent studies have shown that oak trees play a significant role in extracting carbon from the atmosphere, helping to reduce global warming and improve the environment.
In times when coffee beans were not available, acorns from oak trees were often ground up and used to make "Ersatz" coffee, particularly by German troops during the First World War. Acorns can also be ground into flour and used to make bread, a practice dating back centuries among Native American tribes.
Oaks are known as a symbol of strength and steadfastness and have been chosen as a national tree by multiple countries. Oak wood has been used since prehistoric times for construction, and the trees have been associated with many ancient religions around the world, including beliefs from Greek, Roman, and Norse traditions.