This article is the second in a series. Sustainable urban forests are defined as "naturally occurring and planted trees in cities which are managed to provide the inhabitants with a continuing level of economic, social, environmental and ecological benefits today and into the future." In order to achieve the maximum level of benefits, sustainable urban forests must have three components:
The tree resource is the engine that drives urban forests. The urban forest, as a whole, is only as healthy as the quality of the individual trees that make up the forest. In the last article on the new Florida Tree Grades and Standards, we learned how tree quality can be greatly enhanced by selecting trees which have been properly grown in the nursery and demonstrate good trunk, branch and root structure. In this second article on the tree resource, we will explore the concept of tree introduction programs that are designed to improve the urban forest by producing genetically superior trees.
Trees like to grow in the forest. They don't like to grow, and often won't survive in the city. In the forest, they have fresh air, rich soil, and ample moisture. In the city, they have just the opposite. In the forest, each tree is surrounded by other trees; in the city, each tree is surrounded by concrete.
Here in Florida, as with the rest of the developing world, the vast majority of the original forest is already gone. Even with aggressive land acquisition and resource conservation programs, Florida has less than 100,000 acres of old growth or undisturbed habitat left, about 0.2% of the state. Unfortunately, many trees that are planted in the man-made urban landscape die or perform poorly because of the stresses encountered. In order to achieve environmental sustainability, we need trees that are more tolerant to the stresses of urban environments such as soil compaction, cold winters, hot summers, drought, air pollution, salt and insect and disease infestations. Trees that are more tolerant of common stresses will not only survive and perform better, but will result in lower maintenance and replanting costs.
Green Infrastructure The Elemental Solution an article by Pepper Provenzano on Urban Forestry and the future of American cities |
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Fortunately there is tremendous genetic potential for developing superior landscape trees. Dozens of universities, botanical gardens, arboretums, research institutions, and private tree nurseries across the country have long strived to improve tree quality by cloning individual trees which exhibited superior speed of growth, growth form, color, bark pattern and fruit. Unfortunately, few trees currently grown and sold as clones in the nursery trade have been purposely developed and thoroughly tested for disease and pest resistance, environmental tolerance and adaptability. And very few Florida trees have been cloned for landscape use. Compare this situation with the practice of the largest shade tree nursery in the United States, located in Oregon, which produces well over 250 cultivars (named clones) of deciduous trees in 82 species for the northern market.
| Tissue-taking Team
Florida Champion Tree Project 
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An example of a successful southern tree clone is the "Bracken's Brown Beauty" southern magnolia cultivar. Developed originally by tree grower Ray Bracken, the "Bracken's Brown Beauty" has proven to be consistently attractive and extremely adaptable in urban planting sites ranging from as far north as Ohio to as far south as Miami. Another recent example of southern tree improvement is the HIGHRISE® live oak cultivar, the first live oak clone to be introduced to the trade by Tree Introductions, Inc. In addition to offering uniformity to the usually diverse live oak shape, the HIGHRISE® clone features a unique genetic trait—the branches tend to grow more upright, rather than spreading, a characteristic which makes the tree a far better choice for street tree or otherwise restricted site planting.
One of the newest, and certainly the most ambitious, efforts to improve southern tree quality through genetic cloning is the Florida Champion Tree Project (FCTP), a non-profit effort with goals to protect, propagate and plant all the Florida state and national champion trees. A champion tree is defined as the largest tree of its species as determined by combining measurements of trunk circumference, height and crown spread. Florida leads the country with 151 national champion trees, few of which are protected and none of which had been propagated until the FCTP began its activities a year and a half ago. Now the FCTP has licensed the ACCELERATOR GROWERS ASSOCIATION to grow state and national champion tree clones in state-of-the-art air-pruning containers in order to produce high quality root systems for long term survival in the urban environment. The FCTP is also joining with other states to form Champion Tree Project chapters around the country.
six essays by Terry Mock |
Can champion tree genetics guarantee a superior tree for the urban forest? Only time will tell because this has never been done before, however, champion trees do possess a very desirable characteristic—the ability to withstand environmental stress over a long period of time in order to reach very large size. This relatively long "endurance test" period may permit more accurate projections about champion tree clone performance than other new clone candidates, chosen for purely aesthetic reasons, which will need decades to reach maturity.
The urban environment is really a series of heterogeneous microclimates. In the future, the success of urban forests will be assured through identification and use of tree clones with superior genetic characteristics putting them in a better position to cope with the unique environments in which we place them.