Tree Identification and Selection: How to Study Efficiently

Domain Review: This topic is one of the [10 ISA exam domains](/blog/isa-arborist-exam-domains-explained) you must master.

Tree ID is often the most intimidating part of the exam for people who didn't go to forestry school. The good news: The exam asks broader questions about how to identify trees rather than showing you a blurry photo of a leaf and asking for the species.

Taxonomy: The Name Game

• Genus: The "Last Name" (e.g., Quercus = Oak). Capitalized.
• Specific Epithet: The "First Name" (e.g., rubra = Red). Lowercase.
• Species: Genus + Specific Epithet (Quercus rubra).
• Cultivar: A "Cultivated Variety" propagated by humans (e.g., 'October Glory'). In single quotes.

Morphology: What to Look For

1. Branching Arrangement:
   • Alternate: Staggered (Most trees: Oaks, Elms, Birches).
   • Opposite: Pairs (MAD Horse: Maple, Ash, Dogwood, Horsechestnut).
2. Leaf Type:
   • Simple: One blade.
   • Compound: Multiple leaflets on one stem (Ash, Walnut, Hickory).
3. Margins: The edge of the leaf (Serrated, Lobed, Entire/Smooth).

Selection: Right Tree, Right Place

Identification is only half the battle. You must pick the right tree for the site.

• Hardiness Zone: Can it survive the winter?
• Soil Volume: Does it have room for roots? (Don't plant an Oak in a 2-foot coffin strip).
• pH Tolerance: Pin Oaks hate high pH (Chlorosis).
• Pest Resistance: Don't plant Ash trees (EAB) or Elms (DED) without a plan.

Study Tip

Don't memorize random trees. Memorize the MAD Horse mnemonic for opposite branching. If you see a tree with opposite branches, you've instantly narrowed it down to 4 families.