Crown closure

Crown closure
Forest Measurement and Modelling.

Crown closure, also known as crown cover, is the percentage of ground covered by a vertical projection of the outermost perimeter of the crowns in a stand. Only the crowns that form part of the upper canopy level (dominant / co-dominant stratum) are used to determine closure in uneven-aged or stands with multiple canopy layers.

Crown closure is used as a measure of stand density and competition. It may also be used in equations that predict stand volume.

Crown closure may be measured on aerial photographs or other remotely sensed images. Often, stands are grouped into classes after the photograph is compared with standard percentage cover images. For example, the SFRI (Natural Resources and Environment, 1999) classified the forests of Victoria into six classes:

  1. Very sparse (1-9%)
  2. Sparse (10-29%)
  3. Low (30-49%)
  4. Medium (50-69%)
  5. Dense (70-84%)
  6. Very dense (85-100%)

Crown closure can be determined by measuring the crown sectional area of all trees in a stand and dividing by the plot area (and expressed as a percentage). This estimate will be greater than estimates based on aerial photography when tree crown overlap.

An estimate of crown closure can be determined from a line (or line intersect) sample. If a randomly oriented line is located (fully) within the stand, then the percentage of that line that falls immediately below a tree crown is an unbiased estimate of the stand crown closure. Inoue (1999) summarises a proof for the line sample as well as point sample estimates of crown closure.

[crownclo.htm] Revision: 6/1999