Center for Urban Horticulture

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How do plants function in harsh urban environments? How do their roots respond to stress? What factors influence the survival rate of trees lining our city streets? How do air pollutants such as ozone affect plant physiology?

The Center for Urban Horticulture was the first, and remains the largest, program in the world devoted to addressing questions such as these about plants in cities. It was founded in 1980 as a joint enterprise of the University of Washington and the private community, and is dedicated to research, education, and public outreach about urban horticulture.

"One-third of the plants on the endangered species list are threatened because of urbanization," explains center director Clement W. Hamilton. A major research thrust of the center is aimed at understanding the factors important in preserving plant species endangered by urbanization.

In one study by Hamilton and Sarah Reichard, a predictive model was developed for evaluating the invasiveness of woody plants introduced to North America. As non-native plants are brought into the area for landscape or other use--English ivy or Scotch Broom, for example--they may invade the ecosystems and threaten to choke out native species. Until Hamilton's study, little was known about the biology of invasive species and, specifically, why some species are invasive while others are not.

Using techniques of multivariate statistical analysis, Reichard and Hamilton successfully determined the factors that distinguish invaders from non-invasive plants. Those factors included seed germination requirements, vegetative reproduction, length of the juvenile period, and length of flowering and fruiting times, among others.

The Center occupies a new facility at Union Bay on the eastern edge of the UW campus. Built entirely with private funds, it manages the plant collections and interpretive programs of the Washington Park Arboretum, comprising over 5,000 species on 200 acres. The Center has live plant collections at the Union Bay facility, including the Marilou Goodfellow Grove of native plants, the Seattle Garden Club Entry Shade Garden, and the McVay Courtyard of Unusual Plants. The Center's Hyde Hortorium contains over 10,000 pressed study specimens of horticultural plants.

Research at the Center also focuses on practical problems that confront the urban landscape. As an example, the summer droughts of the early 1990s spurred interest in drought-tolerant plants such as ornamental grasses, as well as strategies to reduce or eliminate lawns. For years, the only water-wise gardening information available came from California and did not suit Pacific Northwest conditions. In response, the staff of the Center's Elisabeth C. Miller Horticultural Library created an extensive resource facility with information pertinent to this region.

The library was originally built with a gift from the late Pendleton Miller, a Seattle attorney, in 1985. A 1988 gift of $1.2 million from his wife, Elisabeth C. Miller, has enabled the Center to double the library space and create an endowment to help staff the library and to build collections on a wide range of topics, from drought-tolerant species and low-maintenance gardens to ornamental grasses and "edible landscapes." The endowed librarianship is the only position of its kind in the state of Washington.

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