Bonsai Forest

Usually when upper trees are shorter than 15 meters in Real Life, it means that the soil is either too dry (sandy or limestone soil), too wet (bog) or just low on nutrients. It's also common that the forest in that case is sparse.

In some media, it seems that entire forests can be very low-lying (and still can be impassably thick). Sometimes even in biomes you wouldn't expect the same to happen in real life. The reason may be due to technical limitations. Sometimes this is a result of things not being strictly to scale. Sometimes it just seems to be Artistic License.

Some try to prevent that by doing the opposite — gigantic sequoia-like forests. However, there are almost no forests (especially passable forests) which have densely packed thin and tall trees.

Related to Units Not to Scale.

Video Games

 * Runescape has very few trees which reach three times of a human height. This also includes palm trees and rainforests. Eventually in 2011, many of those short trees were gradually replaced by trees of the size of a lamppost.
 * And, after yet another update, the very trees seen pictured above now tower over player characters, at a size befitting an actual maple tree.
 * In Minecraft, the majority of trees are short enough that you can strike the top of the trunk from the ground level. Under the right conditions, saplings became adult trees in a matter of hours, but never grow any taller after that point. Later, trees can now grow very tall and can merge their canopies with other nearby trees, producing an illusion of forestry.
 * Eversion has trees as short as the main character.
 * Trees in War Craft series are rather short as well. This is not the case in World of Warcraft, where they are realistically sized.
 * The Pokémon series has often very small trees, so much so that a 3' 11" Sudowoodo is mistaken for a tree in Pokémon Gold, Silver, and Crystal Versions, as well as in the remakes HeartGold and SoulSilver Versions.
 * Dwarf Fortress trees are never higher than one story tall. As the joke goes, trees are "the size of a dragon". Thousand year old dragons, mythical beasts and giants are also only a single story tall, and it isn't exactly clear how high a z-level actually IS.
 * Trees in Serious Sam had a poor tree growth. Serious Sam II somewhat improves it (Magnor doesn't count since it's a Macro Zone).
 * In the first Black and White game, all trees were at most twice as big as an adult villager (presumably so that all objects you and your Creature can pick up are of roughly the same size).
 * Trees in the Unreal series are rather small.
 * All the trees in Super Mario 64 are like this.
 * The trees in the various Mechwarrior games are not only short, but they're pencil thin. In addition, they all seem to be skinny, unhealthy-looking pine trees. You never encounter a redwood or even a respectably sized oak.
 * The Legend of Zelda, in 2D versions at least. To a lesser extent, this is also true in the 3D games.
 * Dragon Quest IX has some very short trees.
 * The trees in Animal Crossing are only slightly taller than its characters.
 * Diablo II have rather short trees. It may be justified in the first half of chapter 1 and chapter 5 due to them taking place in moors, stony fields, marshes and tundras where the growth of trees is naturally poor. Chapter 3, however, doesn't have that excuse since it takes place in a rainforest.
 * Morrowind trees contribute to the eerie stagnancy of Vvardenfell (or just remind you of the game's technical limitations).
 * In Scribblenauts, even redwoods are maybe twice Maxwell's height.
 * Averted in The Sims games; trees are an appropriate tree height in comparison to Sims.
 * Both used and averted in Neverwinter Nights. In the Rural tileset, the trees are both ludicrously thick and not exceptionally tall (being about one terrain-height variation tall, or about 5m). On the other hand, the Forest tileset has much more reasonably-spaced trees, all of which grow far past the point where the engine stops rendering (about 20m up).
 * Roller Coaster Tycoon. Even the tallest trees (much taller than average) are more 10 meters than 15.
 * Furcadia's original default trees were not much taller than players with one literally being an oversized bonzai tree. This has been averted with more recent tree additions, some of which are so large they require two items to be placed on the map to make one tree.

Web Original

 * The trees in Petpetpet Habitarium of Neopets are only about thrice as tall as the ladybug-sized insects. Sure, they only have four leaves each, but also have relatively thick brown trunks that indicate these are no seedlings.