One adaptation that oak trees exhibit is very deep root systems, which help them find water. This is especially useful in a habitat that's prone to drought. The leaves of many oaks are thick and have small stomata, which reduces the rate of evaporation and water use.
Oak trees that have large stomata are usually found in hot climates. Larger stomata, which are tiny pores in the leaves, allow the plant to cool down through evaporation.
Other types of oak trees have leaves that curl up in response to drought, or drop their leaves during dry periods. They allow sap to flow easily in early wood when water is plentiful, and slow down the rate of water movement through the cells during droughts.
Oak trees in North America, especially older ones, can tolerate some fires. The evergreen cork oak, which is native to the Mediterranean, grows a thick covering of cork to protect it from fires. Fire removes the competition of less fire-resistant trees, and removes debris from around the oaks. This makes it easier for animals to collect and disperse their acorns. Fire also kills pests, such as moths and weevils, that eat or ruin acorns. Oaks produce more acorns when they're not crowded together with other oaks, allowing for a wider dispersal of oak trees where less crowded conditions allow them to thrive.