Tree crown measurement
Average crown spread is one of the parameters commonly measured as part of various champion tree programs and documentation efforts.
Other commonly used parameters, outlined in tree measurement, include height, girth, and volume.
The other parameter commonly measured, in addition to the species and location information, is wood volume.
[1][2] Data on greatest crown spread is somewhat limited as this parameter is not measured as frequently as are tree height and trunk girth.
The largest recorded is the "Monkira Monster" (Eucalyptus microtheca) located at the Neuragully Waterhole in southwestern Queensland, Australia, which measured 239 feet in 1954.
Robert Van Pelt measured a crown spread of 201 feet of a kapok tree (Ceiba pentandra) at Barro Colorado Island, Panama, in 2003.
Spread should be measured to the tips of the limbs, not to "notches" in the crown shape, and at approximately right angles from each other.
The surveyor locates the point on the ground immediately below the branch tip on one end of the measurements and marks that position.
On steeply sloping ground (over 15 degrees) the taped distance between the two points can be corrected to a true horizontal by using basic trigonometry.
Measurements using a laser rangefinder if made at a steep angle greater need to be corrected for true horizontal distance using the formula above.
[citation needed] When using the spoke method, four or more measurements are taken from the outer dripline of the crown to the side edge of the trunk.
In these cases a series of shots taken to the outer reaches of the branches standing at the side of the trunk can be used to calculate the length of spokes.
In this case the angles will be steep, and the length of a spoke will be: With the increased availability of high-resolution air photos available through Google Earth[6] crowns of individual trees can be distinguished, providing another option for measuring crown spread.
[7] Google Earth itself includes a ruler tool that can be used to measure diameters or spokes across the crown of the tree.
The measurer moves to that next exterior point and repeats the process, continuing clockwise until the crown is encircled.
[citation needed] In the fourth method the measurer does not interact with the trunk or any internal point of the polygon.
This method can also easily be used to measure the areas of other features encountered, for example, tree groupings or vernal ponds.
[citation needed] The USDA Forest Service has published a guidance document[11] on field evaluations of a variety of crown characteristics beyond that of the normally taken basic measurements.
[11][12] Using the card for reference the observer estimates what percentage of the light is being blocked by the crown mass.
Estimates are made from two different directions at right angles and reconciled to determine crown density.
The crown volumes generally cannot be adequately represented by simple geometric shapes due their irregularity in form.
[citation needed] For extremely complex shapes the surface of the crown can be mapped in three dimensions from a series of external or internal survey stations.
From each station the position of a point on the surface of the crown can be mapped using a compass, laser rangefinder, and clinometer.
The exception may be the shallow dome-like crowns of open grown live oak (Quercus virginiana) trees in southern and southeastern United States.
A good description of the general form would be to liken it to the exposed portion of a hemisphere partially buried in the ground.
If they are widely different then the lengths of the axis can be converted to an equivalent circular radius for use in the crown volume calculation using this formula is: This correction is not large.
The length can be calculated based on a bivariate curvilinear regression model using multiple measurement points.
Regression models for parabolas and exponential curve forms have been developed by NTS in Excel spreadsheet format for the benefit of measurers who do not use statistical software.
The spreadsheet fits a parabola to 4 or more points (up to 10 allowed) using the least squares method and then calculates the limb length (s) using Simpson's Rule to evaluate the definite integral.
These lengths are considered to be the top and base of a regular trapezoid with a height equal to the difference in the distance between the two points.
