Urban Trees Help Protect Tampa Bay

Healthy Vegetation Captures Nutrients from Water and Air

By Rob Northrop

As beautiful as they may be, trees growing in Tampa Bay’s watershed provide far more than soothing shade and habitat for wildlife. Healthy trees also are a critical part of protecting Tampa Bay from contaminants, particularly nitrogen compounds that can cause significant underwater damage.

While necessary for life, an overabundance of nitrogen starts a chain reaction that ultimately leads to the loss of seagrasses, a critical habitat for many living organisms. With industry and wastewater sources under control, the majority of excess nitrogen in Tampa Bay now comes from stormwater runoff and atmospheric deposition – and trees help on both fronts.

A single mature tree can intercept between 500 and 750 gallons of stormwater per year, depending upon size, species and rainfall characteristics. Trees reduce the volume of runoff of stormwater by absorbing water in their roots and leaves, slowly releasing water into air or soil. They also absorb many nutrients, including nitrogen, from stormwater.

A study by the non-profit organization, American Forests, estimated that the loss of urban trees in Baltimore-Washington between 1973 and 1997 caused a 19% increase in stormwater. The cost of building stormwater facilities to treat the increased runoff was estimated at $1.08 billion. In Tampa Bay, ongoing studies indicate that 40% to 50% of the nitrogen in the bay falls from the sky as atmospheric deposition.

Each tree growing in an urban area can capture up to 10 pounds of pollutants per year, including nitrogen dioxide, sulfur dioxide, ozone, carbon monoxide and other particulates.

American Forests estimates that the lost tree cover in Baltimore-Washington would have removed about 9.3 million pounds of pollutants from the atmosphere annually – an accomplishment valued at approximately $24 million per year.

Healthy urban tree canopies also can lower city temperatures by up to 20°F, reducing emissions from power plants. Lower summer temperatures even minimize the chemical reaction that produces ground-level ozone and smog.

At the Chesapeake Bay Program – the nation’s largest estuarine restoration project – scientists have identified urban trees as important features and included increasing tree cover as a restoration goal. The program and its partners are now funding pilot projects that demonstrate the practical application of increased tree cover.

Along with improving the bay, homeowners also reap benefits – including cold hard cash. The Center for Urban Forest Research reports that two strategically planted trees may reduce energy bills by up to 25% by the time the trees are 15 years old.

Other researchers have demonstrated that trees add from 5% to 19% to the value of a home. Even business benefits – a survey taken in Georgia found that 74% of potential patrons preferred shops with trees and landscaping, and that those customers were willing to pay 12% more for the products they purchased.

Rob Northrop, urban and community forester with the University of Florida Extension Office in Hillsborough County, was a watershed forester with the Maryland Forest Service involved in the restoration of Chesapeake Bay. To learn more about urban trees in Tampa Bay region, visit urbanforestry.ifas.ufl.edu.