Most pecan growers have observed that training trees to a central leader would be much easier if the tree would only exhibit stronger apical dominance. The fact is, pecan trees have strong apical dominance but that dominance is not expressed in a way we expect or desire. In the photo at right, you can see how a pecan tree breaks bud in the spring. Note that there is a strong flush of new growth emerging from the apex of last year's shoot while buds further down the stem are showing only the slightest bit of green. The cluster of new shoots is expressing apical dominance over the buds below. The lower buds are greening up only to allow catkins (male flowers) to emerge. Vegetative growth from these lower buds will be totally suppressed.
Four new shoots are growing from the top of the shoot pictured above and if left to grow all season these four shoots will develop into a "crow's foot" branch pattern (photo at left). The development of a "crow's foot" at the top of a young tree destroys the central leader, diverting growth to 2-3 leaders (none of them growing straight up).
The way pecan trees break bud in the spring defines the structure of open grown pecan trees. In the photo below, you can recognize how, over the years, the "crow's foot" growth pattern can define the structure of a tree.
You may be wondering--"how in the world did those native pecan trees grow so straight and tall?" The answer is sunlight. Under forest conditions, competition is high and light is limited. The tree puts all its energy into growing a single shoot that can out-grow the competition and reach for sunlight. For open grown pecan trees, multiple shoots grow from the apex to take advantage of the full sun.