Trees have been around on earth for many years, and they have appeared in video games ever since the beginning of video games. They are often referred to as "the lungs of the earth", as trees turn carbon dioxide into oxygen through the Photosynthesis process. Trees can live very long, with some of the oldest reaching several thousand years of age, a fact which is often used in games that feature elves, nymphs, or other forest creatures.
In video gaming, many early developers have hand drawn trees themselves. This can be seen in the seminal adventure game, Mystery House. As technology progressed, developers have used 3d modeling software to render every tree in games. They can then use copies of the tree models to populate the game world. This is can be a lengthy process. Eventually, SpeedTree came along and made this task easier. This software automatically populates the game world of various tree models. Other engines have been used to revolutionize the role and use of trees in games. DICE's Frostbite engine have allowed for the realtime destruction of objects and buildings, this also includes knocking down the rendered trees in game.
Trees serve many different purposes in video games, many of which mirror their real life qualities and aspects. They can be used as a resource such as wood or fruit, such as the case in the Age of Empires franchise. They can be used as cover or obstacles in many first or third person shooters. Trees also can be used as a purely decorative or aesthetic object. This is most evident the the Sims franchise. In many games, especially those that play from an overhead or isometric perspective, trees are used to mark the boundaries of the playable area. In some games, such as the Grand Theft Auto series, they are comically indestructible, unlike many of the other in-game props. They are also usually planted in ridiculously straight rows.
Their ability to change during the seasons allow them to serve as a visual indicator of the season of a game, as evident in games like Animal Crossing. This aspect is also used in certain puzzle situations, as seen in Zelda's Oracle of Seasons, among others.
Trees As Characters
Ever since J.R.R. Tolkien wrote about talking, walking, warrior trees in The Two Towers, the talking tree has become a somewhat common fantasy archetype, one that has certainly worked it's way into videogames, especially RPGs. Harold, from the Fallout series is a prime example, as is the more recent rhyming tree from Dragon Age: Origins.