All botanical markers and tree characteristics should be used when identifying a dormant tree. Tree parts are great but keen observation skills are critical for tree identification in winter. Don't be fooled into thinking that a twig key is the only answer when identifying a dormant tree. A tree identification manual with a key is certainly helpful but your overall observation skills and sizing up a tree will be invaluable even as the twig key is tucked away in your warm library. Get to know a tree and its parts, or "markers", and how these parts look in every season - especially in winter.
A tree crown can give you valuable clues to finding a tree's botanical name by unique crown shape, fruit and/or their leftover containers, persistent leaves, live twigs and growth habit. Trees easily identified by their crown "markers" and growth habit are oak (acorns and persistent leaves), beech (long, pointed buds), hickory (stout twigs), sweetgum (remnant fruit and corky twigs), sycamore (remnant fruit), willow (drooping limbs), dogwood (dried fruit raisins), ash (pitchfork branch ends) and elm (zig-zag twig).
You can identify many trees simply by looking at the trunk. A trunk's bark might be the only marker you will ever need for identifying many tree species. A bark's texture and color can quickly eliminate all other trees. Trees easily identified by their bark markers are beech (smooth bark), river birch (salmon pink, smooth and flaky), aspen (whitish smooth), sycamore (exfoliating camo bark) and hackberry (bumpy bark).
A tree's roots, basal sprouts and litter around the tree base can contribute to an ID. Look for root systems that are partially above ground and show unique markers. Look around the tree base for leaf and fruit litter. Trees easily identified by their basal markers are beech (human-like roots and sprout rings), baldcypress (knees), and all leaf and seed producers that shed.