The basic requirement of the Tree Preservation Ordinance is that all applicable sites retain a minimum tree density of as defined in Section 8. The term "unit" is an expression of basal area (a standard forestry inventory measurement), and is not synonymous with "tree". A single tree equal to one tree unit is between 13 and 14 inches in diameter.

This density requirement must be met regardless of if the site had sufficient tree density prior to development. For these sites, the density may be achieved by counting existing trees to be preserved, planting new trees, or some combination of the two as represented by the formula below.

SDF=EDF+RDF

SDF (Site Density Factor) The minimum tree density to be met on a development site, expressed in units per acre.

EDF (Existing Density Factor) The total number of tree density units measured or calculated based on trees that will remain as conserved on site.

RDF (Replacement Density Factor) The density or total unit value of new trees to be planted on a site.

The Site Density Factor (SDF) is calculated by multiplying the number of site acres units per acre required.

Tree density calculations for a 2.2 acre example residential site would be as follows:

2.2 acres X 20 units per acre equal a SDF of 44 units.

Trees Inventoried in Tree Save Areas

The Existing Density Factor (EDF) is calculated by converting the diameter of individual trees to density factor units using Table A.

Therefore, with a Site Density Factor requirement of 44 units, a Tree Save Area totaling 44.6 Density Units satisfies the Site Density Requirement. These trees will be protected in a Tree Save Area.

To determine Tree Density on large sites, sample areas should be taken in areas to remain undisturbed. Use an approved timber cruising method (50' x 50' sample areas or Prism Method sampling). Flag the sample areas onsite and delineate locations on Tree Preservation Plan.

TABLE A
Conversion of Existing Tree Diameters (DBH) to Density Factor Units

The unit value of an individual tree 41" or greater shall be determined by using the formula: (Diameter) ² x .7854 ÷ 144

Replacement Density Factor (RDF) - If enough trees do not exist onsite to meet the tree density requirements, replacement trees will be needed. Calculate the RDF by subtracting the EDF from the SDF.

For instance, if it was determined that the 2.2 acre sample site mentioned earlier had only enough existing trees to yield a 30 unit per acre EDF, then replacement trees totaling 14 density factor units would be required.

SDF (44) - EDF (30) = RDF (14)

The density factor unit value for each caliper size of replacement (new) trees is shown in Table B. Replacement tree caliper is measured at a point on the trunk six inches from the base for trees up to an including 4" caliper and 12 inches above the ground for trees larger than 4" caliper.

TABLE B
Conversion of Replacement Tree Caliper to Density Factor Units

The values in Table B shall also be used to determine the quantity of replacement trees needed for any Specimen Tree recompense planting. This planting is additional to planting required for Site Density requirements.

Pasture Land Reduction

It is recognized that some properties, or portions of them, may be devoid of trees due to agriculture use. In these cases a reduction of minimum tree density is warranted for new developments. In areas that meet the description of pasture land, the required minimum tree density shall be ten units per acre.

Wooded Site SDF is calculated by multiplying the number of total site acres by 20.

EXAMPLE: a 10 acre site has a SDF of 10x20 = 200 units

Pasture Land SDF is calculated by multiplying the number of total site acres by 10.

EXAMPLE: a 10 acre site has a SDF of 10x10 = 100 units

Mixture of wooded and pasture land SDF is calculated using each component's unit per acre requirement.

EXAMPLE: a 10 acre site has 8 acres wooded and 2 acres pasture land a SDF of (8x20 = 160 units) + (2x10 = 20 units) for a total SDF of 180 units

Easement Exclusion

Properties possessing natural gas, petroleum or electric power transmission easements, or major sanitary sewer main (greater than eight inches in diameter) or water main (greater than 16 inches in diameter) distribution easements, may exclude the land area contained in the easement from the total acreage of the property in fulfilling the Site Density Factor provided that no improvements (e.g., parking lots, tennis courts, driveways, storm water detention facilities, etc.) are proposed within the easement. If any improvements are proposed within the easement, then the land area so utilized within the easement for improvements shall be included in the Site Density Factor requirements.

Lake and Pond Exclusion

Properties with an existing lake or pond greater than one acre in size may exclude the land area contained in the lake or pond from the total acreage of the property in fulfilling the Site Density Factor.

Industrial Development Exclusion

Large industrial buildings for headquarters, manufacturing, warehouse distribution and similar uses often cover the majority of a development site. In addition, the development of the site for a single industrial building typically requires a significant amount of tree clearing and grading. Considering these unique development conditions for this land use, 100% of the building footprint may be excluded from site density calculations if the following conditions are met:

1.

Property is zoned LI or HI

2.

Minimum building footprint is 30,000 square feet

Partial Exclusion of Buffers from Tree Density Requirements

When designing a site, tree preservation shall not be limited to unusable, remote areas of the site. Tree preservation areas should be more evenly distributed around these sites. The intent is to preserve some natural characteristics of the site, such as quality existing vegetation, Specimen and Heritage Trees for aesthetics and conservational purposes.

In an effort to preserve trees and other natural vegetation within a development, 50% of the required post-development tree density shall be met outside stream bank and zoning buffer areas. The tree requirement cannot be fully satisfied by trees in buffer areas. The area of a development outside buffer areas must separately meet at least 50% of the required per acre tree density, even if trees in buffer areas would compensate or more than compensate.

Example:

30 acres x 20 units per acre = 600 units

600 units x 50% = 300 units minimum to be provided outside the buffer areas

A combination of trees save areas, preserved Specimen and Heritage trees and quality replanted trees will be used to meet this requirement within this developed area.

It is understood that many times open or sparsely vegetated zoning buffers will require supplemental or complete planting to meet visual screening requirements; therefore, trees planted for this purpose may count towards the SDF or Specimen recompense replanting.

Tree save areas that include trees preserved within 100' of delineated wetlands and/or ephemeral streams that are specifically protected as part of the design of a project may apply 2x the unit value in Appendix C - Table A of these protected trees towards site density. Entire wetland or ephemeral channel and entire CRZ of all credited trees must be protected to apply this credit.

(Ord. No. 2015-O-11, Exh. A, 12-15-15; Ord. No. 2021-O-007, § 1, 3-16-21)