How Charleston's tree mitigation laws and tree banks work | SC Climate and Environment News - The Post and Courier

How Charleston's tree mitigation laws and tree banks work | SC Climate and Environment News | postandcourier.com

Every month, we receive questions and concerns from people in and around Charleston related to flooding, government regulations and sea-level rise. We read every single one.

Now we are answering some of them in the pages of The Post and Courier. Our Rising Waters Q&A appears every other Monday. Email questions to tcox@postandcourier.com and jchester@postandcourier.com.

Trees, which define the Lowcountry landscape, are admired for their beauty and valued for their benefits.

They protect communities from flooding by soaking up stormwater that would otherwise become run-off, provide reprieve from rising temperatures and improve air quality.

Trees always seem to be on the hearts and minds of Lowcountry residents, who are often quick to come to their defense.

This month, you asked us how tree mitigation laws work, including how the City of Charleston determines which trees need to be replaced and how tree bank funds work. How does the city, and other surrounding municipalities, determine how much money a tree is worth and which are worth replacing?

Here’s what we found out.

When a grand tree is removed, how many trees are replanted in its place?

Trees are defined by their size (diameter at breast height) and species. Protected trees measure 8 inches in diameter at breast height or greater and exclude multi-stem crepe myrtles. Grand trees measure 24 inches or greater in diameter at breast height and exclude pine trees and sweet gums.

The City of Charleston’s zoning code restricts the number of protected trees that developers can remove on a single parcel. Removing any grand tree is prohibited, unless the developer gets prior approval from the Board of Zoning Appeals.

The city’s zoning administrator, Eric Schultz, says that approval to remove grand trees comes with conditions to mitigate the loss of those trees, and these conditions depend on the grand trees’ species.

The city created four categories of trees based on their rating for Charleston’s climate by the International Society of Arboriculture about 20 years ago, according to Schultz.

“Category I trees are trees that you'll find readily in the Lowcountry,” Schultz said. “(They) perform very well and grow in long durations, so live oak, southern magnolia, bald cypress and red maple.”

Category II trees include pecan, southern red oak and sassafras; Category III trees include persimmon, black walnut and princess trees; and Category IV include mulberry, willow and Japanese cherry.

Replacement doesn't require a tree for a tree but rather depends on the diameter of the trees being removed. Mature trees’ diameter is measured at breast-height, roughly 4.5 feet from the ground. Younger trees’ diameter is measured 6 inches from the root ball and are called “caliper inches” in the tree care industry.

Saplings purchased from nurseries or wholesalers typically measure 2.5 caliper inches, which is used as the industry standard.

Category I trees require 100 percent mitigation; Category II trees require 75 percent; Category III trees require 50 percent; and Category IV trees require 25 percent.

“If it's a 24-inch (Category I) tree … you're going to mitigate 24 caliper inches 1 to 1,” Schultz said, noting this would be roughly 10 saplings.

A 24-inch Category II tree would require roughly seven saplings to be planted, a 24-inch Category III tree would require roughly five saplings, and a 24-inch Category IV tree would require roughly two saplings.

The trees planted do not need to be the same species as the trees removed, but Schultz says they need to be the same type of tree.

“A maple tree is considered a canopy tree … so they can present to me a number of different species to replace the red maple as long as they are canopy trees, and that's okay because we want to encourage diversity throughout the landscape of native trees,” Shultz said. “We don't want a monoculture.”

Schultz added that he advocates for these mitigation trees to be native species but the law doesn’t require it. The decision to plant native or exotic species is up to the developer, he said.

In the upcoming year, the city will rewrite its zoning code and will likely redefine these tree categories to prioritize natives.

“Category I trees are the true staples of the Lowcountry,” Schultz said, adding that Category II trees aren’t far behind, but the trees in categories III and IV tend to be “weed trees” or exotics.

“We'll probably be looking at this more closely with the zoning rewrite because we don't want to encourage any invasive species to be planted,” he said. “We want those eradicated, actually, because they're taking over our maritime forest.”

The zoning code rewrite will be the first major update to the code since 1966.

How does the city’s tree mitigation fund work?

Depending on the size of the site, it might not be possible to fit in all of the required caliper inches for mitigation.

Schultz said he’ll run the leftover inches from what couldn’t be planted on site through a formula to determine how much the developer needs to pay into the city street tree program.

This formula divides the number of tree inches a developer removes by the industry standard for saplings (2.5 inches) to get the number of trees, which is then multiplied by the city’s standard of $295 per tree.

One hundred inches of trees removed, divided by 2.5 caliper inches would be 40 trees, said Schultz, which would be $11,800 paid into the tree fund.

Schultz emphasized that paying into the tree fund is only an option for developers if there isn’t enough room to plant all of the required replacement trees. The first goal, he says, is always to get new trees planted on site.

About $90,000 is in the city’s fund. Most of this money came from developers paying for trees that couldn't be planted on site, and some from fines paid for removing trees without approval.

Surrounding municipalities, including North Charleston, Mount Pleasant and Charleston County, have similar tree mitigation requirements.