1. Delimit the geographical area to be sampled.
2. Carry out a preliminary survey on the availability of suitable trees before deciding on
the tree species and size of the sampling units, in order to avoid many units with no
trees.
3. Select a geographical grid for obtaining an even location of sampling units across the
geographical area. Sampling units are located at the intersection points of the
geographical grid.
4. Choose a sampling area ranging from 0.25 km2 (for large-scale studies) to 1 km2 (for
small-scale studies) which must then be used throughout the survey. The shape of the
sampling unit can be rectangular, quadrat, or
circular.
5. Establish the number of trees (x) to be
sampled in each unit according to the
availability of suitable trees (see sampling
procedure), and project requirements.
Recommended ranges are 4-8 trees for
studies where a rather imprecise estimate of
lichen data is sufficient, 9-12 when a greater
precision is required.
6. If fewer than x trees are available in any area,
use the following standard procedure to shift
the unit to be sampled: