(4) Influence of heat: Trees require a certain amount of heat. They receive it partly from the sun and partly from the soil. Evaporation prevents the overheating of the crown. The main stem of the tree is heated by water from the soil; therefore trees in the open begin growth in the spring earlier than trees in the forest because the soil in the open is warmer. Shrubs begin their growth earlier than trees because of the nearness of their crowns to their root systems. This also explains why a warm rain will start vegetation quickly. Too much heat will naturally cause excessive drying of the roots or excessive evaporation from the leaves and therefore more water is needed by the tree in summer than in winter.
(5) Influence of season and frost: The life processes of a tree are checked when the temperature sinks below a certain point. The tree is thus, during the winter, in a period of rest and only a few chemical changes take place which lead up to the starting of vegetation. In eastern United States, growth starts in April and ceases during the latter part of August or in early September. The different parts of a tree may freeze solid during the winter without injury, provided the tree is a native one. Exotic trees may suffer greatly from extreme cold. This is one of the main reasons why it is always advisable to plant native trees rather than those that are imported and have not yet been acclimatized. Frosts during mid-winter are not quite as injurious as early and late frosts and, therefore, if one is going to protect plants from the winter’s cold, it is well to apply the covering early enough and to keep it on late enough to overcome this difficulty.
The mechanical injuries from frost are also important. Snow and sleet will weigh down branches but rarely break them, while frost will cause them to become brittle and to break easily. Those who climb and prune trees should be especially cautious on frosty days.
(6) Influence of air: On the under side of leaves and on other surfaces of a tree little pores known as stomata may be found. In the bark of birch and cherry trees these openings are very conspicuous and are there known as lenticels. These pores are necessary for the breathing of the tree (respiration), whereby carbonic acid gas is taken in from the air and oxygen given out. The process of assimilation depends upon this breathing process and it is therefore evident that when the stomata are clogged as may occur where a tree is subjected to smoke or dust, the life processes of the tree will be interfered with. The same injurious effect results when the stomata of the roots are interfered with. Such interference may occur in cases where a heavy layer of soil is piled around the base of a tree, where the soil about the base of a tree is allowed to become compact, where a tree is planted too deep, or where the roots are submerged under water for any length of time. In any case the air cannot get to the roots and the tree suffers. Nature takes special cognizance of this important requirement in the case of cypress trees, which habitually grow under water. Here the trees are provided with special woody protuberances known as “cypress knees,” which emerge above water and take the necessary air. See [Fig. 18].
Conclusions: From the foregoing it will be seen that trees have certain needs that nature or man must supply. These requirements differ with the different species, and in all work of planting and care as well as in the natural distribution of trees it is both interesting and necessary to observe these individual wants, to select species in accordance with local conditions and to care for trees in conformity with their natural needs.
[Chapter V]
What Trees to Plant and How
The following classification will show the value of the more important trees for different kinds of planting. The species are arranged in the order of their merit for the particular object under consideration and the comments accompanying each tree are intended to bring out its special qualifications for that purpose.
Conditions for tree growth in one part of the country differ from those of another and these lists, especially applicable to the Eastern States, may not at all fit some other locality.
[Trees Best for the Lawn] | ||
|---|---|---|
| Deciduous | ||
| 1. | American elm (Ulmus americana) | One of the noblest of trees. Possesses a majestic, wide-spreading, umbrella-shaped crown; is easily transplanted, and is suited to a variety of soils. |
| 2. | Pin oak (Quercus palustris) | Has a symmetrical crown with low-drooping branches; requires a moist situation. |
| 3. | European linden (Tilia microphylla) | Possesses a beautiful shade-bearing crown; grows well in ordinary soil. |
| 4. | Red maple (Acer rubrum) | Shows pleasing colors at all seasons; grows best in a fairly rich, moist soil. |
| 5. | Copper beech (Fagus sylvatica, alropurpurea) | Exceedingly beautiful in form, bark, and foliage and possesses great longevity and sturdiness. It is difficult to transplant and therefore only small trees from 6 to 10 feet in height should be used. |
| 6. | Coffee tree (Gymnocladus dioicus) | A unique and interesting effect is produced by its coarse branches and leaves. It is free from insects and disease; requires plenty of light; will grow in poor soils. |
| 7. | European white birch (Belula alba) | A graceful tree and very effective as a single specimen on the lawn, or in a group among evergreens; should be planted in early spring, and special care taken to protect its tender rootlets. |
| 8. | Gingko or Maiden-hair tree (Gingko biloba) | Where there is plenty of room for the spread of its odd branches, the gingko makes a picturesque specimen tree. It is hardy and free from insect pests and disease. |
| 9. | Horsechestnut (Æsculus hippocastanum) | Carries beautiful, showy flowers, and has a compact, symmetrical low-branched crown; is frequently subject to insects and disease. The red flowering horsechestnut (A. rubicunda) is equally attractive. |
Fig. 92.—A Lawn Tree. European Weeping Beech. | ||
| 10. | Sugar maple (Acer saccharum) | Has a symmetrical crown and colors beautifully in the fall; requires a rich soil and considerable moisture. |
| 11. | Soulange’s magnolia (Magnolia soulangeana) | Extremely hard and flowers in early spring before the leaves appear. |
| 12. | Flowering dogwood (Cornus florida) | Popular for its beautiful white flowers in the early spring and the rich coloring of its leaves in the fall; does not grow to large size. The red-flowering variety of this tree, though sometimes not quite as hardy, is extremely beautiful. |
| 13. | Japanese maple (Acer polymorphum) | It has several varieties of different hues and it colors beautifully in the fall; it does not grow to large size. |
| Coniferous | ||
| 14. | Oriental spruce (Picea orientalis) | Forms a dignified, large tree with a compact crown and low branches; is hardy. |
| 15. | Austrian pine (Pinus austriaca) | Is very hardy; possesses a compact crown; will grow in soils of medium quality. |
| 16. | Bhotan pine (Pinus excelsa) | Grows luxuriantly; is dignified and beautiful; requires a good soil, and in youth needs some protection from extreme cold. |
| 17. | White pine (Pinus strobus) | Branches gracefully and forms a large, dignified tree; will thrive on a variety of soils. |
| 18. | European larch (Larix europaea) | Has a beautiful appearance; thrives best in moist situations. |
| 19. | Blue spruce (Picea pungens) | Extremely hardy; forms a perfect specimen plant for the lawn. |
| 20. | Japanese umbrella pine (Sciadopitys verlicillata) | Very hardy; retains a compact crown. An excellent specimen plant when grouped with other evergreens on the lawn. Does not grow to large size. |
| 21. | Mugho pine (Pinus mughus) | A low-growing evergreen; hardy; important in group planting. |
| 22. | Obtuse leaf Japanese cypress (Retinospora obtusa) | Beautiful evergreen of small size; hardy; desirable for group planting. |
| 23. | English yew (Taxus baccata) | An excellent evergreen usually of low form; suitable for the lawn, massed with others or as a specimen plant; will grow in the shade of other trees. There are various forms of this species of distinctive value. |
[Trees Best for the Street] | ||
| 1. | Oriental sycamore (Platanus orientalis) | Very hardy; will adapt itself to city conditions; grows fairly fast and is highly resistant to insects and disease. |
| 2. | Norway maple (Acer platanoides) | Very hardy; possesses a straight trunk and symmetrical crown; is comparatively free from insects and disease and will withstand the average city conditions. |
| 3. | Red oak (Quercus rubra) | Fastest growing of the oaks; very durable and highly resistant to insects and disease; will grow in the average soil of the city street. |
Fig. 93.—Street Trees. Norway Maples. | ||
| 4. | Gingko (Gingko biloba) | Hardy and absolutely free from insects and disease; suited for narrow streets, and will permit of close planting. |
| 5. | European linden (Tilia microphylla) | Beautiful shade-bearing crown; is very responsive to good soil and plenty of moisture. |
| 6. | American elm (Ulmus americana) | When planted in rows along an avenue, it forms a tall majestic archway of great beauty. It is best suited for wide streets and should be planted further apart than the other trees listed above. Requires a fairly good soil and plenty of moisture, and is therefore not suited for planting in the heart of a large city. |
| 7. | Pin oak (Quercus palustris) | This tree exhibits its greatest beauty when its branches are allowed to droop fairly low. It, moreover, needs plenty of moisture to thrive and the tree is therefore best suited for streets in suburban sections, where these conditions can be more readily met. |
| 8. | Red maple (Acer rubrum) | Beautiful in all seasons of the year; requires a rich soil and considerable moisture. |
[Trees Best for Woodland] | ||
| For Open Places | ||
| 1. | Red oak (Quercus rubra) | Grows rapidly to large size and produces valuable wood; will grow in poor soil. |
| 2. | White pine (Pinus strobus) | Rapid grower; endures but little shade; wood valuable; will do well on large range of soils. |
| 3. | Red pine (Pinus resinosa) | Very hardy; fairly rapid growing tree. |
| 4. | Tulip tree (Liriodendron tulipifera) | Grows rapidly into a stately forest tree with a clear tall trunk; wood valuable; requires a fairly moist soil. Use a small tree, plant in the spring, and pay special attention to the protection of the roots in planting. |
| 5. | Black locust (Robinia pseudacacia) | Grows rapidly; adapts itself to poor, sandy soils. The wood is suitable for posts and ties. |
| 6. | White ash (Fraxinus americana) | Grows rapidly; prefers moist situations. Wood valuable. |
| 7. | American elm (Ulmus americana) | Grows rapidly to great height; will not endure too much shade; does best in a deep fertile soil. Wood valuable. |
| 8. | European larch (Larix europaea) | Grows rapidly; prefers moist situations. |
Fig. 94.—Woodland Trees. Red Oaks. | ||
| For Planting under the Shade of Other Trees | ||
| 9. | Beech (Fagus) | Will stand heavy shade; holds the soil well along banks and steep slopes. Both the American and the English species are desirable. |
| 10. | Hemlock (Tsuga canadensis) | Will stand heavy shade and look effective in winter as well as in summer. |
| 11. | Dogwood (Cornus florida) | Will grow under other trees; flowers beautifully in the spring and colors richly in the fall. |
| 12. | Blue beech (Carpinus caroliniana) | Native to the woodlands of the Eastern States; looks well in spring and fall. |
[Trees Best for Screening] | ||
| 1. | Hemlock (Tsuga canadensis) | Will stand shearing and will screen in winter as well as in summer. Plant from 2 to 4 feet apart to form a hedge. |
| 2. | Osage orange (Toxylon pomiferum) | Very hardy. Plant close. |
| 3. | English hawthorn (Cratægus oxyacantha) | Flowers beautifully and grows in compact masses. Plant close. |
| 4. | Lombardy poplar (Populus nigra var. italica) | Forms a tall screen and grows under the most unfavorable conditions. Plant 8 to 12 feet apart. |
