The street tree problem for the Pacific Northwest

Abstract

A regional analysis of the street tree problem has been undertaken in order to evolve a system of tree classification which would be useful to city planners, arborists, and landscape architects who have the responsibility of selecting trees to fulfill their design requirements for the city street. Three lines of approach to the problem were followed: ecological considerations, an analysis of the controlled conditions of the city environment, and a classification of the various tree characteristics which might affect their selection. The most significant factors of environment in relation to the selection and use of trees are climate and soil. Of these, separate classifications have been made under the major headings of soil, water, temperature, light and atmosphere. An analysis of the apparent reactions of the various trees to these factors in the Pacific Northwest has been undertaken and suitable trees, from the list of 245 species and varieties, considered as possibilities for street use, have been placed in the classification. The controlled conditions of the city environment have been considered under the headings: types of streets, street widths, building setbacks, planting strips, overhead obstructions, underground services, and building heights. Trees have been selected to suit these city factors and classified under the above headings. The morphological and other characteristics of trees which might affect their selection for street use are: shape, size, root systems, rate of growth, longevity, resistance or susceptibility to diseases and pests, tolerance of city conditions and extremes of environment, flowering and fruiting habits, specific effects (especially seasonal effects), mass and texture. Trees have been selected to suit .a classification based on these characteristics. The punched card system of classification has been used to assemble the results of the three lines of approach to the problem, the code having been prepared from the above factors.