1.3 Core sampling (small bore testing)

1. Purpose of Core Sampling

Core sampling is a non-destructive or minimally invasive method to:

  • Detect the presence, location, and extent of resin in standing trees.
  • Estimate resin quality and density before harvesting.
  • Monitor resin development over time in plantations.

It allows growers to make informed decisions without felling the tree.

2. Equipment Needed

  • Increment borer (small diameter): 5–10 mm core bit.
  • Hammer or T-handle: To drive the borer into the trunk.
  • Core extractor or needle: To remove the wood sample.
  • Marking tape or chalk: For marking sampling points.
  • Plastic bags or vials: To store cores.
  • Notebook or digital recording device: To document findings.

3. Sampling Procedure

  1. Select Sampling Height & Sites
    • Typically 0.5–1.5 m above ground (breast height).
    • Sample multiple points around the trunk (north, south, east, west) for representativeness.
    • Avoid sampling too close to large wounds or infection sites unless specifically monitoring resin development there.
  2. Drill the Increment Borer
    • Insert borer slowly into the trunk, ideally perpendicular to the growth rings.
    • Drill until reaching the pith or desired depth (usually 10–20 cm).
    • Avoid over-drilling, which may stress the tree.
  3. Extract Core
    • Rotate the extractor or use the borer’s wedge to carefully remove the core.
    • Handle cores gently to avoid breakage or contamination.
  4. Inspect Core for Resin
    • Discoloration: Dark brown to black streaks indicate resin zones.
    • Texture/density: Resinous portions are harder, sometimes sticky.
    • Scent: Crush or sand a small portion to detect aromatic compounds.
  5. Record Observations
    • Note tree ID, location, sample height, resin presence, color, and estimated density.
    • Photograph cores for reference.
  6. Seal Boring Holes
    • Apply tree wound sealant or natural clay to prevent infection or pest entry.

4. Advantages

  • Non-destructive: Tree can continue producing resin.
  • Early detection: Identify resin zones before cutting.
  • Repeatable: Same tree can be monitored over time.
  • Quantitative assessment: Core diameter, length, and resin proportion can be measured.

5. Limitations

  • Small cores may miss localized resin pockets.
  • Requires skill to interpret core color and density accurately.
  • Trees may respond with minor wounds; repeated sampling should be spaced appropriately.

6. Best Practices

  • Combine core sampling with visual inspection and scent testing for accuracy.
  • Use sanitized tools to avoid spreading fungi or pathogens.
  • Mark sampled sites to avoid repeated stress in the same area.
  • For plantations: consider periodic monitoring (6–12 months) to track resin induction progress.