Tree Biology and Identification
Meristems and transport
All woody growth comes from meristems. Apical meristems extend shoots and roots; the vascular cambium produces xylem inward and phloem outward; the cork cambium makes periderm. Xylem carries water and dissolved minerals upward. Phloem carries sugars from sources to sinks and can move either direction seasonally. Distinguish heartwood from sapwood, earlywood from latewood, and reaction wood (compression wood in conifers, tension wood in hardwoods).
Injury response
Compartmentalization (CODIT) describes boundary-setting after wounding: wall 1 plugs vessels, wall 2 forms a barrier ring, wall 3 is the ray barrier, and wall 4 is the new cambium that closes over the wound. Trap: trees do not heal or repair damaged tissue; they isolate it. A flush cut removes the branch collar and defeats wall 4, which is why the final cut belongs just outside the collar and branch bark ridge.
Identification
Work from arrangement, then leaf type, then twig and bud detail. Leaf arrangement is alternate, opposite, or whorled. Only a small set of common landscape genera are opposite: maples, ashes, dogwoods, horsechestnut and buckeye, catalpa, and viburnum. Then check simple versus compound leaves, leaf scars and bundle scars, terminal bud presence, bark, fruit, and form. Use a dichotomous key and correct nomenclature: genus capitalized, specific epithet lowercase, cultivar in single quotes, italicized genus and species.
Worked example
A twig with opposite leaves, a true terminal bud, and U-shaped leaf scars containing three bundle scars is an ash (Fraxinus). The same opposite arrangement with no terminal bud and V-shaped scars points to maple (Acer). Rule of thumb: opposite arrangement alone eliminates most of the woody landscape, so confirm it first before keying further.