Bay Soundings l Tampa Bay's Science and Nature News Journal

Photo courtesty National Oceanic and Atmospheric Administration

A new study on tree canopies in Manatee County confirms earlier reports from the city of Tampa — money may not grow on trees, but they’re great investments both for homeowners and a community concerned about air and water quality.

The Manatee study indicates that tree canopy increased by 13% from 2004 to 2009 with a 3% increase in non-woody vegetated ground cover, even as the county’s population increased by 20,000 people. Using CITYGreen software developed by American Forests, ecological and economic values were assigned to the tree canopy within three benefit areas:

And as local governments work to comply with more stringent stormwater regulations at both the state and national level, urban tree canopies could become even more important, notes Rob Northrop, forester with the University of Florida and Hillsborough County Extension.

“Local governments will have a horrendous time meeting new stormwater requirements with conventional engineering technologies,” he said. “The EPA (Environmental Protection Agency) has indicated to the University of Florida that they will consider allowing urban forests to be part of the treatment train to meet those requirements.” Agreements that recognize the impact of an expanded urban tree canopy already have been signed between the EPA and governments in Philadelphia and Washington, DC, he adds.

The city of Tampa, which completed comprehensive reviews of its tree canopy coverage in 1996 and 2006, will kick off an even more in-depth study in spring 2011. Along with an updated inventory, it will include a detailed analysis of nitrogen cycling in urban forests as part of a cooperative agreement with the EPA.

The nutrient study is part of the EPA’s pilot program that aims to place a dollar value on natural resources (see Bay Soundings, Fall 2008) where Tampa Bay was selected as one of four regions for broad-based research on the multiple services trees and other natural features provide.

The nutrient study is part of the EPA’s pilot program that aims to place a dollar value on natural resources where Tampa Bay was selected as one of four regions for broad-based research on the multiple services trees and other natural features provide.

One upcoming study will look at 150 plots in Hillsborough County, including rural, urban and wetland sites, to document the impact of trees on air and water quality. Several major highways will also be included, with studies on how well trees absorb air pollution, specifically nitric oxide that causes acid rain and may be deposited as a damaging nutrient in Tampa Bay.

The city’s study also will include social scientists studying how residents feel about trees and determining the most effective messages to encourage them to support conservation and expansion of urban forests. “Not everybody is educated in ecology or has the technical background to recognize the real value of trees,” Northrop said.

The Manatee study, completed with funds from the Florida Urban and Community Forestry Grant Program and Keep Manatee Beautiful, compared aerial photographs from 2004 and 2009. Unincorporated areas have a canopy coverage of 39% percent, while incorporated areas have a coverage of about 32%.

Urban canopies have not been formally studied in Pinellas County, according to Allan Mayberry, Dunedin city arborist. “My gut feeling is that we’re losing canopy but we’re the state’s most densely populated county and we’re simply running out of space.”

Even the parks are fully planted, he adds, so the city is focused on enhancing trees instead. Dunedin also is pushing for green roofs, a technology that’s been very successful in Europe and other states, although development in Florida has lagged.

“We’re recommending them with almost every site plan that comes in but we’re still looking for the first one to build,” Mayberry said.

A central tenet of Florida-friendly landscaping – right plant, right place – is even more important when planting trees. The wrong tree in the wrong place may not survive, or it may thrive and cause problems for homeowners.

“Live oaks are beautiful trees, but you can’t plant them in an eight-foot strip between two new homes,” says Northrop.

Every site is different, but critical factors to consider when planting a tree include:

Size of the site

Consider both mature height and spread of each tree species. Look up to check for power lines.

Temperature zone

Some trees won’t tolerate freezes, other prefer at least some cold weather to grow well.

The amount of light the site receives

Most trees prefer full sun but some will tolerate shade for part of the day. For optimal energy savings, plant trees where they shade the western and northern walls of your home and roof, or shade your air-conditioning unit.

Soil pH, texture and moisture

Again, some trees demand sandy well-drained soil, others require higher moisture levels.

Deciduous or not

Would the site benefit from seasonal loss of leaves that allows increased sun in the winter?

Seasonal color and fruit

Consider the downsides as well as the benefits. Flowers and fruit typically mean that the tree will shed more.