Trees

Houston’s Regional Forest, a report that evaluates the trees in our eight-county region, was released in the fall of 2005. The report concludes that the region has 663 million trees with a replacement value of more than $205 billion.

Our trees store $721 million worth of carbon; generate $456 million worth of environmental benefits annually, and save $131 million in residential energy costs and avoided power plant emissions each year. They remove move than 60,000 tons of air pollution every year.

The report is the result of a three-year collaboration between federal, state, and local researchers. Data was collected from 332 field plots throughout the eight counties.

The report concluded that the region’s large and very large trees generate the most environmental benefit – 30 percent of the region’s trees are five inches in diameter or greater, but they generate more than 60 percent of total environmental benefits. The Park People’s fourth Harris County Tree Registry, which identifies the largest trees of a species, was published in 2005.

Land use changes and invasive tree species are significant threats to the regional forest. Between 1992 and 2000, forest cover declined by 17 percent, resulting in a net loss of over 78 million trees. The most common tree is the invasive Chinese tallow, which now makes up 23 percent of all trees in the Houston region. In the southern agricultural part of the region, almost 80 percent of all trees are tallows. The report notes that several other tree species – tree-of-heaven (Ailanthus altissima), chinaberry, Chinese privet, mimosa – have escaped cultivation in the region. It warns that several other non-native species that are being promoted as landscape trees have the potential to become invasive. This list of trees includes Chinese pistache, Chinese elm, Mexican white oak, and sawtooth oak.

The Texas legislature passed two bills that provided incentives for tree planting and the federal transportation bill includes an appropriation of about $15 million for tree planting along area freeways.

If you have wondered why local businesses all seem to have the same landscaping plan – a low hedge between evenly spaced trees – it is because Houston has an ordinance that requires that parking lots be screened from public streets by a tree or shrub barrier, that trees be planted adjacent to public streets at the rate of one tree per 30 feet of frontage, and that parking lots have one tree for every ten parking spaces. In 2005, Harris County passed regulations requiring landscaping for all new single-family residences and commercial developments in unincorporated areas of Harris County. The regulations are modeled on the Houston ordinance. City and county regulations also prohibit removal of trees within rights of way and impose special requirements for large trees. Houses on lots that are smaller than 5,000 square feet must have one tree; two trees are required if the lot is larger. Trees must be 1.5 caliper inches or larger.

Winds from Hurricane Rita resulted in significant damage to trees across the eastern part of our region. For example, at Martin Dies Jr. State Park, 40 to 50 percent of the tree canopy was lost, according to Texas Parks and Wildlife estimates. In addition, falling trees caused many downed power lines, resulting in power outages that lasted for weeks in some areas.

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