A wolf tree is an unusually large tree which dominates the surrounding environment because of its size. Wolf trees tend to have a very large crown, and to be heavily branched. They are also usually older than the surrounding trees, although this is not always the case. Many natural forests have wolf trees, and these trees can also be spotted in settings where people are taking a relatively hands-off approach to forest management.
Classically, a wolf tree is a tree which managed to survive when an older stand of trees was damaged or significantly depleted, making it at least a generation older than the surrounding trees. For example, a single tree might be left after clearing to create a meadow, a stand of trees might be damaged by fires or storms leaving one or two survivors, or a stand might be heavily logged, leaving only a few trees behind. In these cases, the elimination of other trees allows a wolf tree to grow big and strong, because there is no competition, and younger generations grow up around it.
In forest management, a wolf tree can represent a problem. It usually eliminates competition in the surrounding area by monopolizing nutrients and sunlight, making it difficult for other trees and shrubs to grow. It may also not have very much financial value, as older trees can become twisted and knotty, making their timber largely useless. Wolf trees are aesthetically interesting, however, and they often provide habitat for animals, so they do in fact have ecological value.
The origins of the term "wolf tree" are a bit obscure. A variety of theories have been put forward, including the idea that such trees are like "lone wolves" because they tend to grow alone and isolated since other trees cannot survive around them. Others have suggested that since many cultures have historically thought of wolves as thieves, people coined the term "wolf tree" to describe a tree which was perceived as a thief of resources.
Dominant trees do, of course, seed new generations of their own, and they do eventually die, allowing new generations to grow up and take their place. These trees are often of interest to human visitors to the forest, and they can also make useful landmarks when people are giving directions. Telling people to look for a large or unusually shaped tree can help people spot the landmark well in advance, making it easier to follow directions.