How do I estimate Tree Basal Area (TBA)?

Trees mostly reduce pasture growth in grazed woodlands, so the trees need to be measured to account for their impact on current and potential pasture growth, and thus carrying capacities.

Delineate areas of your paddock that may differ in tree density. If the land type in which you are working has trees scattered relatively evenly over the whole area, one or two measurements averaged, should be enough for the area. However, if the trees are thicker in some areas than others, take measurements in each area and average for the land type.

Three simple TBA techniques are described below. Regardless of the technique used, as long as it is done consistently, and repeated a number of times at each site, you will be able to get a representative average TBA for your site and monitor changes in TBA over time.

Measure TBA using the pencil technique:

  1. Stand in the middle of a representative area of trees
 or regrowth
  2. Hold the pencil (ideally a HB pencil) vertically at arm’s length.
  3. As you turn in a complete circle, count every live tree in your line of vision with a trunk appearing the same width or wider than the pencil at 30cm above the ground.
  4. Calculate the approximate basal area in square meter per hectare by dividing the figure you counted by four
  5. Input this number in the TBA section of the Stocktake Plus app.

Measure TBA using the Stocktake Plus dendrometer technique:

NB: The dendrometer within Stocktake Plus has only be optimised for iPhone 4+.  If using another device, check your results with another technique.

  1. Stand in the middle of a representative area of trees
 or regrowth
  2. Hold your device vertically approximately 50cm from your eye.
  3. Launch the Stocktake Plus Dendrometer from the app
  4. As you turn in a complete circle, press the – or + to count the number of live trees with a trunk width (30 cm above the ground) the same or wider than the middle sight bar.
  5. Input this number in the TBA section of the Stocktake Plus app.

Measure TBA using the Sapling TBA calculator:

If saplings dominate an area, this technique will provide a better TBA measure than using either of the above techniques.

  1. If saplings are very dense count the number of saplings in a 10m strip 1m wide, and estimate their average diameter at approximately 30 cm from the ground.
  2. Input these numbers into the Stocktake Plus app sapling TBA calculator to convert to TBA m2/ha.
  3. If sampling density is not very high, then you may need to sample a bigger area (e.g. 10m x 10m square).