The Economic and Environmental Benefits of Urban Trees
Forests and trees are faced with many factors that can adversely affect tree populations and their associated values to people, the economy, and ecosystems. These threats include extreme weather events, wildfire, insect pests, and land cover changes.
Pests
Because the region's forests are dominated by certain tree species, the structural and functional values of the forest are at risk from pests that target these potential hosts. The total value of losses sustained during a serious outbreak of any one of these pests could be in the billions of dollars.
Invasive Tree Species
The movement of trees and plants across the globe for horticultural and agricultural purposes as dramatically affected ecosystems in the southern U.S. Some plants were chose for their aesthetic qualities or to perform some particular function while others are "stowaways" that arrived in shipments of other plants or animals. Chinese tallow was introduced in Texas in the early 1900s as a potential agricultural source of seed oil to make soap. However, it quickly escaped cultivation. It appears highly adapted to areas disturbed by human activitiy including agriculture, forestry and land development. Once established, Chinese tallow tends to dominate areas by outcompeting native plants. In this regard, it has become the dominant tree species in the Houston region accounting for over 152 million trees. It makes up nearly 80 percent of all trees in the South Agriculture/Range cover and 13 to 19 percent of trees in the Forest cover types.
Land Cover Changes - 1992 to 2000
Urban development and other human activities in the Houston region have had significant effects on the regional forest's extent and composition. The current study compared LANDSAT satellite data for 2000 and U.S. Geological Survey land cover data for 1992 to estimate land cover changes that occurred over this more recent eight-year period.
The Forest land cover types declined by a total of 17.4 percent, an annual loss of 2.2 percent. The Agriculture/Range lands stayed roughly the same with the expansion of Residential and Urban Built land cover accounting for most of the Forest land cover loss. The land cover changes had a dramatic effect on the total number of trees, with an estimate loss of over 78 million or roughly 10 million trees per year.
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