By Matthew Weaver

Trees have always been a vital part of our world and a crucial factor in our sustainability. It is important that we realize trees’ and forests’ true function and value to our everyday lives. Over the past 40 years we have lost close to a quarter of our forest canopy in the region due to development and land use change, this means looses could total over 25 million trees annually. As population and development explode across the nation we must consider keeping trees in the forefront of policy and decision making that effects our future. Over 85% of our population across the U.S. lives in urban areas, however, when we think of a forest we often then to think of rural and natural places. In recent times, due to technology and an overall awareness and advancement of the field of urban forestry, we can now look at trees and measure their value in several areas. One key factor in contributing to the advancement of forestry is that we can now attribute economic values to these benefits using scientific research and modeling. Being able to asses a dollar amount to the benefits enables decision and policy makers to incorporate trees and forests as infrastructure and an economically viable resource. Trees in urban areas should be viewed as infrastructure just as streets, sidewalks, stop lights, etc. Trees, if properly maintained, are one of the few infrastructure items that actually appreciate over time and the benefits will far outweigh their cost to cities and communities.

Urban trees and forests in and around the Greater Houston Metropolitan Region have a significant economic and environmental impact on the area. Studies throughout the nation have shown that urban forest can help improve air quality by reducing air temperatures, directly removing pollutants from the air and by reducing building energy use and consequent pollutant emissions from power plants. Because of this, in 2000, the USDA Forest Service Region 8 Cooperative Forestry Division approved funding of a special project, called UFORE (Urban Forests Effects model), to investigate the effects of trees in the Houston Metropolitan area on air pollutant concentrations. The goal of this project is to provide evidence of urban tree effects on air quality so tree management can become an integral part of clean air planning and policies in Houston. Based on a sample 332 one-sixth acre field plots and recent satellite analyses within the eight-county (7581 mi2 not including water) Houston area (Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery, and Waller), the following information is preliminary data estimated for the forest and urban forest resource:

• Number of trees: 663 million

• 84 million of total tree population is in urban areas

• Percent forest cover: 28.4%

• Air pollution removal (annual): 60,575 tons ($295.7 million)

• Carbon storage (total): 41.8 million tons ($840 million)

• 10.7 million tons of storage comes from urban trees

• Carbon sequestered (annual): 2.1 million tons ($44 million)

• Annual savings due to energy conservation from trees: $131 million

• Structural or replacement value (total): $205.9 billion

Other major benefits such as stormwater management are also crucial to our region. Studies have shown our regional forest can save $1.3 billion in avoided retention/detention cost and for every 5% increase in canopy coverage, stormwater drainage is reduced by 2%. There is no doubt that trees also improve our quality of life by improving mental and physical health, increasing property values, and increasing sales in retail centers. Studies have also shown that people who live in communities with trees get along better with their neighbors and crime is reduced.

The regional forest surrounding Houston is diverse, particularly comparing the northern and southern regions. The highly diverse pine-hardwood forests in the North Forest has larger trees, more species and more overall forest coverage, with loblolly pine the single most common species. The South Forest includes forests dominated by Cedar elm, hackberry, and hawthorn as well as old growth Columbia bottomland hardwood forests, plus expanding regions of invasive Chinese tallow. The Houston forests contain high biological diversity with nearly 70 dominant species. The majority of the Houston region’s 663 million trees are young; nearly 75% are less than 5 inches in diameter.

Large trees are disproportionately important in terms of forest benefits. Although large trees comprise less than a quarter of the region’s trees, they provide the majority of air pollution, carbon storage, and energy savings benefits. Protecting the region’s large trees is essential for sustaining the forest benefits. At an estimated 7% mortality rate, sustaining Houston’s current tree canopy requires planting or natural regeneration of 2 million new trees per year.

Urban development, invasive tree species, and insect pests pose significant threats to the future of the regional forest. Actions that significantly alter land cover have reduced the number and density of tress while providing opportunities for invasive species and unhealthy forest conditions. The non-native invasive species Chinese tallow is currently the single most abundant species in the region at 23% of all trees. Land use continues to threaten forests: Between 1992 and 2000, the city proper lost over 50% of its forest cover (over 300,000 trees), the South part of the region lost over 50% of its forest cover (1 million trees), and the North part of the region lost 1% of its forest cover (100,000 trees). Insect pests are not an imminent threat, but a major infestation could cause harm to urban forests at extensive economic costs.

To ensure that the benefits of trees will be experienced by future generations, local and regional leaders must develop long-range policies for maintaining and expanding tree cover. Besides affecting the rate of impact of land use change, one way to minimize these losses is to reduce tree mortality rates. Improving landscape care and maintenance programs while increasing large scale tree plantings, are vital to achieving a healthy and sustainable urban forest.

Cooperators in the UFORE study are the U.S. Forest Service, The Texas Forest Service, TCEQ, University of Houston, Houston Advanced Research Center (HARC) and the Houston Green Coalition (a group of municipal, and non-profits working towards utilizing trees as a tool for meeting air quality standards). The Texas Forest Service was the Project Manager.

Weaver lives in Fort Bend County along the Brazos River.

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