GOV DOC 3QH BOSTON PUBLIC LIBRARY 3 9999 06583 419 2 #A '^m The Greening of Boston: Trees and Shrubs in the City $lr " -•-iisjjy Crab Apple Flowering Dogwood Ginkgi Crah Apple Sycamore Maple The Greening of Boston: Trees and Shrubs in the City 014 B65P The Boston Foundation. AUTHOR. - :, Th e Greening of Boston: TITLE Trees and Shrubs in the City. D14 B65P The Boston Foundation. This book is for every resident of Boston who has helped make a neighborhood a pleasing place to live . . . and for the late Bessie Barnes, whose efforts on her own Greenwich Street in the South End inspired us all Doston is a green city. Everywhere one encounters trees and shrubs that have adapted to life in this densely populated urban area. The greening starts in the Com- mon and the Public Garden. From there it extends down Commonwealth Avenue to the Fens, and then to Jamaica Pond, the Arboretum, and Franklin Park. This "Emerald Necklace" is highly visible; but it is in the small parks and squares and along the streets of Boston's neighborhoods that people have more frequent daily contact with the pleasure and beauty of trees, shrubs, and flowering plants. Boston's first urban planners wanted to create a healthy and diverse environment for people in the city. Their early achievements have been sustained by generations of resi- dents who committed their civic energy to planting trees along city streets and estab- lishing green spaces. Today we recognize just how much the people of Boston use and enjoy plants. Trees and shrubs provide shade, windbreaks, and privacy; they have practical value to the city dweller. They have aesthetic value as well; their masses of green foliage, seasonal flowers, fall color, and winter silhouettes add greatly to our visual appreciation of the city. The fact that plants now surround us should not be taken for granted. The greening of a city is a process. Like the recycling of old buildings and the reshaping of city neighbor- hoods, greening requires energy and imagina- tion on the part of each new generation. Planting trees and shrubs is not a task that, once completed, can be ignored. It takes ongoing effort to keep plants thriving in any urban setting. This publication has been prepared for the residents of Boston. It is a guide to the best trees and shrubs for planting in the city — plants that are hardy, tenacious, and pleas- ing to the eye. Basic methods of care and feeding are also described. We want to en- courage residents all over the city to plant trees and shrubs, and to help maintain new and old plantings in the face of urban stresses. The greening of the urban landscape continues to depend on people. Greenwich Street, Umier Roxhiry Plants in an Urban Environment Sunlight, temperature, wind, rain, and snowfall are variable weather conditions that make climate. They affect what plants we can grow and where we can grow them. Cities such as Boston are generally warmer than the smrounding suburbs. To the city dweller this means earlier blossoms and longer periods free of frost. In the early spring, commuters notice that daffodils and forsythia are blooming in Boston but still dormant in the suburbs. Trees leaf out earlier in the city than in the suburbs. This phenomenon is caused by the "urban heat island." The "island" is warmed by the tremendous energy pouring out of industries, by commercial and resi- dential heating systems, and by the release of heat stored in building and pavement surfaces. Rainwater, which cools suburban land surfaces, disappears quickly down city gutters and catch basins. Even the cloud of pollutants, hovering over the city like an insulating blanket, holds in heat. Boston's weather is notoriously changeable. Our pre- vailing west-to-east weather flow collides periodically with air movements coming down from Canada and up from the tropics, producing sudden changes. Boston's seacoast position also subjects it to coastal storms, "northeasters," which bring strong winds and heavy rain or snow. The Atlantic Ocean moderates tempera- ture extremes: Boston's famous sea breezes cool steamy summer afternoons, while the relatively warm seawater lessens the severity of winter cold. Plants moderate the effects of city climate. Deciduous trees provide cooling shade, while evaporation of water from their leaf surfaces helps to lower summer tempera- tures. In winter, the same trees allow warming sunlight to shine through their leafless branches onto streets, sidewalks, buildings, and into windows. Trees and shrubs can also control and redirect harsh winds, making walk- ing more pleasant for pedestrians. Trees and shrubs help reduce urban pollution. Plants are natural filters. They take carbon dioxide from the air and return oxygen to it; they also remove limited quantities of sulphur dioxide and hydrogen fluoride, which are common pollutants, from city air. Plants filter out dust, pollen, ash, and smoke by trapping airborne particles on the tiny hairs that coat their leaves. The particles are regularly washed off onto the ground by rainfall. Plants also decrease other urban irritants such as noise and light glare. Tree trunks and large branches somewhat disperse sound waves, while leaf masses absorb them. Light glare is reduced by trees and shrubs that screen automobile headlights, streetlights, floodlights, and obtrusive neon signs. Plants of the proper size, shape, and density can be used effectively to lessen many disturbing qualities of city life. Birds and other wildlife survive in the city because trees and shrubs offer them food, shelter, and breeding places. Squirrels, pigeons, and other birds— even an occasional rabbit— help animate the city and make the out-of-doors more interesting. Boston's green spaces attract both local and migratory birds. A great variety of visiting waterfowl is observed annually on Boston's rivers and ponds and in the Fens. In every part of the city where green spaces are preserved, different species of landbirds are commonly seen. From time to time, the Massachusetts Audubon So- ciety issues reports of unusual bird sightings .^fifi^,, in Boston and its vicinity: baned owls in Cambridge, cerulean and yellow-throated warblers in Mt. Auburn Cemetery, a gyr- falcon at the Prudential Center! Plants are essential to attract and protect .--<'■- resident and visiting wildlife. .-.-- : ^ f f Especially important are ,• y , ■'.. *; - 4- native fruit-bearing ,#l|^fc trees and shrubs. ^Sk^' •^8*^-^ >%>-' Trees and shrubs make an important contribution to the architecture of urban spaces. Their shapes complement buildings, both old and new. Their textures and shadows enhance the variety of building materials in the city: brick, wood, stone, concrete. Trees and shrubs also provide a comfortable transition from the human to the larger building scale. In parks and gardens, they form areas of privacy and places for retreat from intense city activity. Each day, trees and shrubs give the city dweller the opportunity to observe the processes of nature: subtleties of seasonal change, plant growth, and the varying char- acteristics of plant shape, texture, flowers, and fruit. But unlike forests, wetlands, and prairies, the city's green spaces are not self-sustaining. They are remote from the more balanced ecology of rural lands and are de- pendent on human care. Trees and shrubs can be successfully grown in the city only when urban stresses are understood and countered with responsible planting and maintenance. Plants do not dirive when the light they need is blocked by build- ings, when they receive insufficient water, or when they suffer in compacted soil. The need for sunlight and water is common knowledge. Less well-known is the fact that compacted soil limits the circulation of air around roots, and that this air— or the oxygen in it— is critical to the survival of any plant. Additionally, salt used for de-icing streets and sidewalks is particularly harmful to the root structure of trees and shrubs, quickly killing the surface roots and eventually affecting the entire plant. The list of hazards to trees and shrubs in the city is long: excessive air pollution, poor soil, wounds from cars and trucks, vandalism, and carelessness during con- struction. These stresses damage and kill plants; they also weaken their natural resistance to insect attacks and disease. But most of these threats to city plants can be avoided by proper planting and care. Informed resi- dents can be aware of the health and well-being of their neighborhood trees and shrubs. And most important, they can participate in the simple tasks that preserve the lives of plants and enhance their natural growth and beauty. i^vIImi'J Trees and Shrubs Recommended for Planting in Boston 1 Street Trees Ginkgo (Ginkgo biloba) Green Ash (Fraxinus pennsylvanica lanceohta) Katsura (Cercidiphyllum japonicum) Little-leaf Linden (Tilia cordata) London Plane (Platanus acerifolia) Norway Maple (Acer platanoides) Pin Oak (Quercus palmtris) Red Oak (Quercus borealis) Sweet Gum (Liquidambar styracifhta) Sycamore Maple (Acer pseudoplatanus) Thomless Honey Locust (Gleditsia triacanthos inermis) Tree of Heaven (Ailanthus altissima) Japanese Zelkova (Zelkova serrata) Ornamental Trees Amur Maple ( Acer ginnala) Bradford Callery Pear (Pyrus calleryana 'Bradford') Cornelian Cherry (Comus mas) Crab Apple (Malus varieties) Flowering Dogwood (Comus florida) Hawthorn, Washington and Lavalle (Crataegus phaenopyrum, Crataegus lavallei) Japanese Dogwood (Comus Kousa) Magnolia, Saucer and Star (Magnolia soulangiana, iiastellata) Evergreen Trees Austrian Pine ( Pinus nigra) Hemlock, Canadian and Carolina (Tsuga canadensis, Tsuga caroliniana) Japanese Black Pine ( Pinus thunbergii) White Fir (Abies concolor) Deciduous Shrubs Chinese Witch Hazel (Hamamelis mollis) Cotoneaster, Rock and Spreading (Cotoneoster horizontalis, Cotoneaster divaricata) Flowering Quince (Chaenomeles varieties) Forsythia (Forsythia intermedia, Forsythia 'Arnold Dwarf) Japanese Green Barberry (Berberis thunbergii) Lilac (Seringa varieties) Rose of Sharon (Hibiscus syriacus) Scarlet Firethorn ( Pyracantha coccinea) Spirea (Spiraea varieties) Viburnum (Viburnum varieties) Broad-Leaved Evergreen Shrubs Azaleas (Rhododendron varieties) Inkberry (Ilex glabra) Japanese Holly (ilex crenata) Mountain Andromeda (Piens floribunda) Rhododendron (Rhododendron varieties) Evergreen Shrubs Japanese Yew (Taxus cuspidata) Juniper Quniperus varieties) mm Me/n/le Avenue, Dorches Street Trees The following trees are recommended for planting on Boston's streets. They are selected because they are hardy in the Boston area; that is, they grow well under local conditions of temperature, rainfall, and soil. They tolerate the stresses of pollution, wind, and limited area for root develop- ment. Their shapes are strong and recognizable. At maturity they attain a height of fifty to sixty feet. They are reasonably resistant to insects and disease, and need minimum specialized care. Nurserymen and plant scien- tists are constantly developing new varieties of trees that respond well to the particular pressures of the city environment. The new varieties appro- priate to Boston are included in this section. A variety of trees should be planted on city streets. There is a very real danger in planting a limited number of species in a city because uncon- trollable insect and disease attacks can demolish thousands of trees in a single species (Dutch elm disease is a sad and poignant example). Planting a variety of tree species on city streets prevents such disasters and also make a richer landscape. Street trees are the backbone of a green city. They produce masses of green foliage in the summer, intense autumn color, and a lovely tracery of branches in the winter months. Note: scale is Vi" = 5' Cjinkgo (Ginkgo bibba) Male Only One of the most beautiful and exotic trees for city planting. A native to China, the ginkgo is sometimes known as the maidenhair tree because of the similarity of its distinctive fan-shaped leaves to those of the maiden- hair fem. It is a wide-spreading, open-crowned tree with strong ascending branches that occasionally reach out beyond the general outline of foliage. The leaves turn a clear yellow in the autumn. It is almost totally resistant to attacks from insects and disease, and it survives moderate amounts of wind, soot, and other air pollutants. The female tree produces fruits with a very unpleasant odor, therefore only the male tree should be planted. The 'Sentry' variety, which is quite narrow and upright, is a recently developed form. (jjreen Ash (Fraxinus Pennsylvania! Janceolata) The green ash grows rapidly, is drought-resistant, and survives in relatively poor soils. It is pyramidal in shape, with glossy, dark green foliage that turns bright yellow in the autumn. Native to the eastern and central United States, the green ash has been growing wild in Boston along the banks of the Muddy River for many years. Because the female tree produces quanti- ties of seed pods which litter city sidewalks and produce hundreds of chance seedlings, the variety 'Marshall's Seedless' is recommended for street planting. Ixatsura (Cercidiphyllum japonicum) The katsura has distinct grace and delicate beauty. The heart-shaped leaves are rose-colored in the spring, blue-green in the summer, and yellow to scarlet in the autumn. When grown with a single trunk, the katsura makes an excellent street tree. It is generally vertical when young, becoming wide- spreading at maturity. Multitrunked specimens make excellent lawn trees. It is markedly resistant to pests and disease, but needs deep watering to survive. A native of Japan, the katsura is just now gaining popularity as a street tree in many eastern cities. % ! Little-leaf Linden (Tilia cordata) ^---i^ii^^K The little-leaf linden is the great avenue tree of Europe. Equally successful in this country, the linden is planted extensively by architects and de- signers, who are attracted to the dense symmetry of its htanching pattern. The linden is oval-shaped, and has a strong and interesting winter silhouette. The dark, almost black bark is enhanced by heart-shaped, deep-green leaves that turn yellow-gold in the autumn. Linden flowers are produced in great numbers at the end of June and are very fragrant. Lindens do best in fertile soil and with ample moisture. The 'Greenspire' variety has a conspicuously narrow top, as opposed to the typical oval shape. London Plane (Platanns acerifolia) ^ ==== ^ The London plane has a strong, straight trunk with distinctive mottled gray to tan bark which exfoliates, or naturally peels off. The bark is a familiar sight to generations of city dwellers. The London plane is a natural hybrid between the American sycamore and the oriental plane tree. It grows rapidly, produces good shade, and is particularly hardy along the seashore. The London plane is susceptible to anthracnose, a disease which can dis- figure the leaves; it can be controlled by spraying with a fungicide. A new variety, 'Bloodgood', which is resistant to anthracnose, has been developed and is just now being planted in Boston. %» Ag>) ;:.j $.;,f IN orway Maple (Acer platanoides) The Norway maple is fast-growing and tolerant of both persistent wind and moderate amounts of pollution. It is a popular and widely planted tree in Boston. It is, however, a shallow- rooted tree. Many of the feeder roots are very close to the surface, so the tree is susceptible to damage from com- pacting of the earth at its base and from salt used for de-icing. The base area of the tree should be protected. Several varieties of Norway maple are now being planted in Boston: 'Columnare', a dense and narrow form; 'Sum- mershade', a heat-resistant variety; 'Swedleri', with red leaves in the spring that gradually turn green in summer. 'Crimson King', with red leaves throughout the growing season, has been widely planted in Boston but should be used sparingly as a specimen or accent tree. I Pin Oak (Qnercus palustris) The pin oak is easily recognized by its dense pyramidal branching pattern; the upper branches ascend to a narrow crown; the lower ones sweep almost to the ground. The deeply indented leaves turn a dark red in the autumn. The pin oak is native to the United States and is used as a street tree in many cities, with lower branches pruned to prevent interference with traffic. The pin oak resists wind damage. It also survives the transplanting process better than most oaks. The variety 'Sovereign' is a new form with regularly upright branching. ,,si ■ ■ 4! *i||K 4C 35' - — 30' 25' 20' ^Sp^ ? './■ ■■ 15' IfS Amur Maple Green Ash Red Oak Cornelian Cherry vp&y ^^r i^PS''""'^ It Li trie-leaf Linden Magnolia Norway Maple V-i ^f Bradford Gallery Pear Japanese Zelkova Japanese Dogwood 1