ISA Exam Glossary: Core Terms You Must Know

If you don't know the words, you can't answer the question. The ISA exam uses technical terminology. Here are the heavy hitters you need to memorize.

Biology

• Meristem: Tissue where cell division (growth) occurs.
  • Apical: Tip growth (height/length).
  • Cambium: Girth growth (diameter).
• Xylem: Transport tissue for water and minerals (Up). Wood is xylem.
• Phloem: Transport tissue for sugars (Down/Around). Inner bark is phloem.
• CODIT: Compartmentalization Of Decay In Trees. (Wall 1: Plugging, Wall 2: Latewood, Wall 3: Rays, Wall 4: Barrier/New Wood).

Pruning

• Collar: The swollen area at the base of a branch. DO NOT CUT THIS.
• Included Bark: Bark pinched between two stems. A sign of weak structure.
• Lion Tailing: Removing all inner foliage, leaving tufts at ends. Bad practice (increases limb failure).
• Topping: Cutting back to stubs or laterals too small to assume dominance. Forbidden.

Soil & Water

• Cation Exchange Capacity (CEC): The soil's ability to hold onto nutrients (clay/organic matter = High CEC; Sand = Low CEC).
• Infiltration: Rate at which water enters the soil.
• Percolation: Rate at which water moves through the soil.

Risk & Safety

• Target: People or property that could be hit by a falling tree. Without a target, there is no risk.
• Kickback: The violent backward/upward motion of the chainsaw guide bar nose.
• MAD: Minimum Approach Distance. How far you must stay from power lines (10ft for distribution lines usually, unless certified for line clearance).

Summary

This is just a starter list. Whenever you see a bold word in the study guide, write it down!