Certain features contribute to the structural strength of the trunk and main branches of trees.

Wide-angled branch attachments are stronger than those with narrow angles.  A wide angle between branch and trunk allows strong connective wood to form in the crotch as well as on the sides and the lower portion of the branch attachment.  A narrow angle of attachment may result in bark becoming imbedded between the branch and trunk.  Little or no connective wood forms in a sharp-angled crotch, which is inherently weak.

Such narrow-angled branches may be strongly attached and in their early years most of the weight will be nearly parallel to the axis of the branch and truck.  In later years, these branches become heavier and more spreading, and are apt to split out during a storm.  Such losses not only deform the tree but are dangerous.

In training a young tree, a potential primary scaffold branch developing with narrow angle of attachment should be removed as soon as possible.

You may be able to choose another branch with a wider angle of attachment.  If not, a second branch may grow from the same node and will usually have a much wider angle of attachment than the first.  Also, since its growth begins later, it will have a smaller diameter in relation to the trunk than the first branch, permitting the branch attachment to be stronger.

Most broadleaved plants have more than one bud at a node, but usually only one develops unless growth is quite vigorous.  The wider angle of attachment of a branch from a second bud at a node is particularly evident when the buds are superposed (one above the other) as in ash and walnut.

Trees of some species may occasionally have branches forming extremely narrow angles of attachment.  Their attachment may be acute enough to cause indentations in the trunk, or they may twine around the trunk and look very picturesque.  But to avoid the possibility of later splitting out, they should be removed.

Certain trees-for example, Lombardy poplar, have been selected for their erect branching (fastigiate) habit.  The upright branches of such trees are not removed.  Usually they are relatively small compared to the trunk.

Laterals should be smaller than the trunk or branch from which they arise.  Whenever a trunk or branch forks, one branch of the fork should be larger than the other.  If the angle of attachment is wide, the larger trunk or branch can form supporting wood completely around the smaller branch so that the limbs will fit together like a dowel in a chair leg.  The branch attachment will grow stronger with each year of growth.

Estimate the size (diameter) of trunk and lateral just beyond the point of attachment.  If the lateral is too large in relation to the trunk, remove some of its leaves or leaf buds.  If the branch has laterals, these may be thinned.  If the branched has none or few, it should be headed.

In many trees, the lowest branch outstrips the growth of the trunk and the upper branches.  In developing a trunk, therefore, check regularly during the growing season to see that the lower laterals do not outgrow the leader.

Tapered trunks will withstand greater stress (wind, vandals) than those that have little or no taper.  A tapered trunk decreases in diameter with height.  When a tapered trunk bends (top figure), the curvature is fairly uniform throughout its length and allows more uniform distribution of stress.  Tops of well-tapered trunks bend under the wind further from the vertical than those with less taper, reducing the danger of broken trunks or other deformation from exposure to the wind and undeformation from exposure to the wind and uneven stress distribution.  During the growing season, the tip of the leader may bend so far that it is parallel to the wind load, which relieves almost all stress on the immature wood of the tip.

Temporary branches will increase total tree growth, even though the tree may not grow quite as rapidly in height as it would with no temporary branches along the trunk.  This slight reduction in height growth is definite advantage in developing a structurally strong tee.

Leaving temporary branches along the trunk and allowing the trunk to flex in the wind not only will increase trunk taper.  This will greatly reduce and sometimes eliminate the length of time a tree must be staked.