Apical dominance in plants is the main stem of the plant, spurting with growth from its bud, due to the growth hormone called auxin IAA (from the Greek word auxein, which means 'to increase'). The central stem has a predominant apical bud that grows a lot faster than the lateral one, which enables the plant to grow in order for it to meet basic requirements for its basic mechanisms and functions of photosynthesis, water, nutrient uptake, cell division and enlargement, cellular respiration in plants, and the like. The proliferation and growth for the need of dominance is in the apical meristem.
The main reason for which the foliage fights in order to be competent for its linear growth, is mainly sunlight. Plants, which need a lot of sunlight, fight in aggressive silence for receiving it, the sun being a major element required for photosynthesis. The larger plants hamper and dominate the growth of smaller plants, thus rendering them weaker and unfit to survive. As plants grow and where apical dominance is prevalent, there are always nodes and internodes to add to the branching out of more stems. Lateral buds of a tree are dormant compared to the apical bud. The latter is the most active one, after which comes the lateral bud where branches grow laterally to the main stem, and the least active is the root bud. It is usually the dicotyledonous trees or the trees with tap-roots, which are competent in their dominance in order for them to grow faster so that they survive. Monocotyledonous plants, grass, for instance, aren't quite so rigorous with this need.
Meristem has dense cytoplasm and less vacuoles. Cytoplasm is the fluid holding all the cell structure together. Vacuoles play an important role in maintaining balance between the generation of the required cell-structure and other substances, and degeneration of those, which are not required. The apical meristem is the origin of the main shoot for the plant, where it builds newer cells that create newer tissues, and thus becomes a main formative region for further growth. Despite the distinct features of every plant, the function and organization of all meristems holds essentially alike for dominance. The meristem ascertains absorption of sunlight in order for the roots to dig deeper in the soil, and for the entire plant to have a solid and firm holding in the soil, by way of apical dominance. It is the supply of auxin in the apical bud that makes them so. Lateral meristems are called 'vascular cambium' in many plants.
After the tree reaches a certain height, the stems thicken and the plant becomes stronger and begins to gain the appearance of a full-fledged tree. This dominance factor is more pronounced in young plants than it is in older ones.
Pruning takes advantage of this biological behavior of the plant, by cutting off the apical bud in a way for the tree to branch out for either aesthetics or its health. Apical dominance is used to control a tree's growth by cutting the more dominating bud in order for the dormant lateral ones to grow.
As the tree grows, the auxin concentration in its apical bud declines as it travels down the stem in order to assist the tree in other cell-forming and growth processes. Otherwise, trees would never stop growing tall at all and just become a lank mass of a stem that can bear neither wind nor weather. Thus, I hope a gist about the dominance feature has been assimilated.