Crown closure

Aerial Overview of Crown Closure

Crown closure is a term used in forestry.

Crown closure, also known as canopy cover, crown cover, or canopy closure, is defined as the percent of canopy overlying the forest floor.^[1] Another definition of crown closure is the proportion of a stand covered by the crowns of live trees.^[2]

Basic concepts

Crown closure helps predict volume, stand density, crown width, and crown competition factor. Crown closure is often determined using aerial photographs because ground evaluations become difficult to obtain. Stands are usually placed in to different classes (1-6) after viewing the aerial photographs.^[3]

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%

Although sometimes referred to as canopy cover and canopy closure, crown closure is different from these two concepts. Canopy cover represents the aggregate of all vertically projected tree crowns onto the ground surface, while canopy closure represents the amount of the sky obscured by the canopy from a certain point on the ground.^[4]

Ground measurement

Each tree’s measurements are used to calculate the area projected by the crown onto the ground. Summing the crown areas for all trees measured on a fixed plot area and dividing by the ground area will give the crown closure. The "moosehorn" crown closure estimator was an early device for measuring crown closure from the ground.^[5] Other methods for estimating crown closure include the use of line-intercept, spherical densiometer, and hemispherical photography.^[6] Exact cover measurements should be made in vertical direction, or the cover percent will be overestimated.^[4]

Aerial measurement

Aerial photographs made at scales of 1:15,000 or larger can be used to determine crown closure estimates, usually done by ocular interpretation, by grouping stands into percent classes.^[1] Low density stands make for an easy ocular estimation, but as the stand density increases the ocular estimates become more difficult to obtain. In dense stands, over estimates or under estimates of crown closure can be made and predicting value of stand volume becomes more reduced.^[2]

References

1. ^ ^{a b} Avery, T.E. and Burkhart, H.E. 2002. Forest Measurements. 5th edition. McGraw Hill, New York. 456 p.
2. ^ ^{a b} Spur, S.H. 1952. Forest Inventory Ronald Press, New York. 476p.
3. ^ Brack, Chris. 1999. Crown Closure. ANU
4. ^ ^{a b} Jennings, S. B., Brown, N. D., & Sheil, D. 1999. Assessing forest canopies and understorey illumination: canopy closure, canopy cover and other measures. Forestry 72(1): 59–74.
5. ^ Garrison, G.A. 1949. Uses and modifications for the "moosehorn" crown closure estimator. Journal of Forestry 47(9):733:735.
6. ^ Fiala, A.C.S.. Garman, S.L., and A.N. Gray. 2006. Comparison of five canopy cover estimation techniques in the western Oregon Cascades. Forest Ecology and Management 232:186-197.