Forest coverage can be estimated in one of the following methods, depending on the size and topography of the property, the number of trees on the property, and the availability of suitable aerial photographs. The table below shall be used to determine the minimum forest coverage that must be retained during land clearing, land disturbance, and/or development or achieved through replanting with trees and shrubs recommended in the Lake Lure Tree Management Handbook. Copies of all materials used to arrive at tree density or canopy coverage estimates must be presented with the site plan.
The ground survey significant tree density. With this method, a qualified licensed professional shall visit the area on foot (at the owner's expense), count or (if necessary) estimate the number of significant trees before clearing, and report the significant tree density. Significant trees, and/or significant forest areas, shall be marked on the plat for protection or removal as described in section 28-109. Estimates of significant tree densities that will remain after land clearing, land disturbance and/or development shall be based on the number of significant trees to be removed. Where this density falls below that required on the Forest Coverage Table, the tree protection officer shall direct the replanting of trees to make up the deficit.
The aerial survey canopy coverage. A property with steep topography or significant forest coverage might best be managed by a canopy coverage estimate involving analysis of existing aerial photographs. This analysis shall be carried out by a qualified licensed professional, at the owner's expense, by the method described under aerial survey-canopy coverage method at the end of this attachment.
The combined ground and aerial survey. When an area to be evaluated by aerial survey also includes pockets of forest that are to be left for greenspace or common areas, or small undisturbed forest areas (less than one acre and less than 50 percent canopy coverage) that will be disconnected from larger undisturbed forest areas, these isolated areas shall be evaluated by a ground survey, with the significant tree density figure to be shown on the plat for each such isolated area. This method will improve accuracy in calculating overall forest coverage, particularly where common areas and greenspace are so designated. The significant tree density method shall also be used when planning tree thinning on a portion of the property or for other special purposes needing particular accuracy.
Other methods. Property owners wishing to compute the pre-land clearing/land disturbance/development forest coverage estimate by their own methods shall provide their calculations to the tree protection officer with sufficient clarity and accuracy that the tree protection officer can duplicate and validate their results.
The Forest Coverage Table. This table computes the minimum significant tree density or canopy coverage that shall remain on a property after land clearing, land disturbance, and/or development, based on the significant tree density or canopy coverage on the property prior to land clearing, land disturbance, and/or development. Where these values fall below those required on the Forest Coverage Table, the tree protection officer shall direct the replanting of trees to make up the deficit.
Forest Coverage Table
Pre-Land Clearing/Land Disturbance/Development Significant Tree Density (Significant Trees per Acre) | Pre-Land Clearing/Land Disturbance/Development Canopy Coverage (Percentage of Total Property Area) | Post-Land Clearing/Land Disturbance/Development Significant Tree Density Or Canopy Coverage |
0 to 10 | 0% to 10% | 1.0 x initial value |
11 to 20 | 11% to 20% | 0.90 x initial value |
21 to 50 | 21% to 50% | 0.80 x initial value |
50 or more | 50% or more | 0.70 x initial value |
Examples
Tree density example. For a 200-acre subdivision development with an average initial significant tree density of 25 significant trees per acre, the final significant tree density (after accounting for roads, facilities, homes and driveways) shall average 20 significant trees per acre (.80 x 25).
Canopy coverage example. For a 200-acre subdivision development with an initial canopy coverage of 25 percent, the minimum final canopy coverage (after accounting for roads, facilities, homes and driveways) shall be 20 percent of the 200-acre development (.80 x 0.25).
Aerial survey-Canopy coverage method
Step 1: Using a clear, 2005 or later aerial photo of the property, draw a grid overlaying the property. The grid lines shall be spaced at one-half inch intervals. Count the total number of squares in the grid, then study the squares and estimate each square's coverage level - the percentage (100 percent, 75 percent, 50 percent, 25 percent, or zero percent) of each square that is covered by forest canopy.
For squares with 100 percent canopy coverage, a value of 1.0 shall be assigned.
For squares with 75 percent canopy coverage, a value of 0.75 shall be assigned.
For squares with 50 percent canopy coverage, a value of 0.5 shall be assigned.
For squares with 25 percent canopy coverage, a value of 0.25 shall be assigned.
For squares with zero percent canopy coverage, a value of 0 shall be assigned.
Step 2: Count the number of squares with 100 percent coverage and multiply by 1. To calculate the percentage of the total property area that the 100 percent coverage squares represent, divide the number of 100 percent squares by the total number of squares in the grid. Use the following formula to do the division and convert the results into a percentage:
(a x 1) X | x | 100 | = | (?)% |
x = Total number of squares covering the whole property.
a = Total number of squares with a 100 percent canopy coverage level.
Then count the number of squares with 75 percent coverage and multiply by 0.75. Use the same formula to do the division and convert the results into percentages.
(b x 0.75) X | x | 100 | = | (?)% |
x = Total number of squares covering the whole property.
b = Total number of squares with a 75 percent canopy coverage level.
Follow the same steps for the other levels of canopy coverage using the following values:
For the 50 percent canopy coverage.
(c x 0.50) X | x | 100 | = | (?)% |
x = Total number of squares covering the whole property.
c = Total number of squares with a 50 percent canopy coverage level.
For the 25 percent canopy coverage.
(d x 0.25) X | x | 100 | = | (?)% |
For the 0 percent canopy coverage.
(e x 0) X | x | 100 | = | (?)% |
x = Total number of squares covering the whole property.
e = Total number of squares with a 0 percent canopy coverage level.
When the area percentage for each coverage level is known, add the percentages together for the total estimated canopy coverage as a percentage of the total property acreage.
Example problem: A grid is laid over a two-acre tract. The property has been previously disturbed and shows mixed patches of forest and cleared areas. The total number of squares covering the parcel is 140. 100 squares are completely vegetated; ten squares are 75 percent vegetated; 15 squares are 50 percent vegetated; ten squares are 25 percent vegetated; and five squares no longer contain any vegetation. Using the above equation, calculate the estimated canopy coverage for the site.
Canopy Coverage Estimation of Site
(Code 1989, ch. 91, attach. C)