What's not to love about trees? They provide shade and shelter, and they are the literal homes of an untold number of living things. Across the world, many millions of people depend on trees for their livelihood, and of course we can't forget that they clean the air and help us breathe.

Among trees, though, oak trees are particularly vital and important because they are a keystone species, which is a species that other species in an ecosystem depend on. In the case of oak trees, they support more lifeforms — birds, mammals, insects, fungi and more — than any other genus of tree in North America, according to the U.S. Forest Service.  

The wood from oak trees has long been sought after too. In the era of wooden ships, the white oak and the English oak, a species similar to the white oak that is native to Europe, were the most sought after for shipbuilding. One of the most famed ships in U.S. history, the U.S.S. Constitution of War of 1812 fame, was made of white oak, according to the National Park Service.

So mighty is the oak tree that it was proclaimed the national tree of the United States in 2004, and one species of oak, the white oak, was voted the state tree of Illinois in 1973 by schoolchildren from across the state.

It's not just recently that we've developed an appreciation for these mighty trees. Oaks are steeped in history and legend too. Acorns, the fruit of the oak tree, were for centuries a food source for people across Asia, Europe, North Africa and North America, a practice that continues in some parts of the world today, the park service reports. Even our written history was aided by oak trees, the galls of which were used to create ink. These massive trees have also been a symbol of endurance and strength for cultures dating back to the ancient Celts, Druids, Greeks, Romans, Slavs and Vikings. The use continues today as well, with oak leaves a decorative symbol of military awards and ranks in militaries around the world.

Today, the world is home to about 435 oak species growing on five continents. About 90 oak species are native to North America, the park service reports. They are among the longest-living trees in the world. White oaks, a common oak species, typically live more than 300 years. There's an English oak tree growing in Lithuania that is almost 2,000 years old, and there's a tree called the Jurupa Oak in California that is a colony of Palmer's oak clones that has been alive for 13,000 years!

Our native oak trees can be divided into two groups: white oaks and red oaks, Treehugger reports. Common white oak species include the white oak, bur oak and chestnut oak, while common red oaks include the northern red oak, pin oak, black oak and scarlet oak. One of the primary differences between white oaks and red oaks is how frequently they drop their acorns. White oaks drop acorns every year, while red oaks drop acorns only every other year, according to the National Wildlife Federation.

Oak trees have an easily identifiable leaf shape — long with distinct lobes that have pointed or rounded ends, rounded on white oaks and pointed on red oaks — but it's the fruit of the tree, the acorns, that these trees are really known for. It can take 20 or more years for an oak tree to begin to produce acorns, but once they do they can produce quite a bounty. A single oak tree can produce thousands of acorns a year, totaling 3 million or more acorns over its lifetime, the park service reports. All those acorns don't yield new forests of oak trees, though. Only about one in 1,000 acorns will grow into a new oak tree, the University of California Davis reports.

All those acorns that never grow into new trees aren't wasted, though. Many wildlife species are fond of acorns. More than 100 animals native to the United States eat acorns, and they are considered one of the most valuable food resources for wildlife, according to the National Wildlife Federation. Among the biggest fans of acorns are some of our most recognizable and respected animals — deer, chipmunks, opossums, raccoons, squirrels and birds such as blue jays, crows, quails, wild turkeys and wood ducks. 

Blue jays' penchant for acorns helped spread oak trees far and wide following the last glacial period, according to the Cornell Lab of Ornithology. In the fall and early winter, a white-tailed deer's diet can consist of more than 75% acorns as they try to bulk up for the coldest months, the wildlife federation reports. A bumper crop of acorns is even correlated to an increase in does birthing more twins the following year because their nutrition is improved.

Oak trees' leaves and even its sap also provide nutrition for wildlife, and the trees are also essential habitat for animals big and small. Caterpillars, in particular, can be abundant in oak forests. More than 900 caterpillar species live in the oak forests across the United States, the park service reports. Compare that to another common and recognizable family of trees, the maples. Maple trees only attract 300 species of caterpillars. The number of insect species a tree attracts might seem inconsequential, but more caterpillars and insects means more birds and other wildlife.  

If learning all the benefits of oaks trees is enough to make you want to plant one in your yard, consider starting with a native sapling purchased from a reputable plant nursery. You can, of course, grow an oak tree from an acorn, but remember that oaks are slow-growing trees so you will reap the benefits of having an oak tree nearby more quickly by planting a sapling. 

Make sure to pick a spot for planting that can support the space, light and soil requirements for the tree you select. Dig a hole that is the proper depth and width for your tree, the University of Illinois Extension advises. A common mistake people make when planting trees and shrubs is digging a hole that is too deep, which can make it difficult for the tree or shrub to become established.

Once your tree is planted, add a 2-inch to 4-inch layer of mulch around the planting hole, the extension advises. Do not mulch around the tree trunk. You'll also need to water your tree regularly from June to October for about two years after planting if rainfall is not adequate. Trees need 1 inch to 2 inches of water a week. When watering, use a garden or hose or soaker hose to add water directly to the tree rather than using a sprinkler, which results in a lot of water loss from evaporation.