Planting Design Considerations in Landscape Design
The following criteria shall be considered in planting design:
1. Plant Material
2. Soil conditions
3. Availability and quality of water
4. Availability of sunlight
5. Quality of air
6. Maintenance
7. Functional Aspects of Design with Plants
8. Planting for Shelter and Soil Conservation
9. Air Pollution Control by Plants
1. Plant Material
The major sets of factors that influence the choice of plant material are related to the characteristics, both botanical and physical of plant material and the context in which the plant material is to be used. The inter-relationship of these sets of factors is the basis for developing a sound approach to the process of designing with plants.
Physical and Botanical Characteristics of Plant Material
The information on plant material should be available in a systematic format to include the definition, significance, and design implications of the following aspects:
(a) Nomenclature (botanical and trade name);
(b) Origin, family, and natural habitat;
(c) Growth characteristic and form as a function of habitat;
(d) Physical characteristics, for example, bark, texture, foliage, etc.
(e) Propagation and maintenance; and
(f) Use in landscape design.
Vegetation Types (Evergreen and deciduous): Some examples of the functional implications of using evergreen and deciduous plant material for specific situations are:
(a) Evergreen trees for:
(i) Places requiring shade throughout the year,
(ii) Strong visual screening
(iii) Part of windbreak or shelter planting, and
(iv) Areas where leaf lifter is to be discouraged.
(b) Deciduous trees for:
(i) Greater visual variety,
(ii) Partial visual barrier,
(iii) Areas where under-planting is to be encouraged (for example grass)
(iv) Emphasis on branching and flowering patterns, and
(v) Areas where shade is not required throughout the year.
Growth Rate and Age of Vegetation: Growth rate is directly related to the life span of the tree and slower-growing trees have a life span extending to hundreds of years. Fast-growing trees to the exclusion of slower-growing varieties are not recommended. Landscapes are developed to sustain future generations; slow growing long lived native trees shall be emphatically included in all major planting schemes.
Growth Habits of Various Kinds of Vegetation and Their Form: The overall physical form of a plant is usually the result of the foliage density and branching pattern. It may also be expressed as the proportionate relations between height and canopy spread. The latter is a direct expression of growth habit. The following classification into basic types may be useful.
(a) Trees of fastigiate or columnar habit –
Examples of trees of this type are :
Casurina esquisitifolia (beet wood)
Grevillea robusta (Silver Oak)
Polyathia logifolia (Ashok)
Populus species (Poplar)
Though the branching pattern of each is different, the overall shape is similar
(b) Tall trees with canopy –
Examples of trees of this type are :
Dalbergia sissoo (Sheesham)
Tamarindus indica (Imli)
Terminalia arjuna (Arjun)
The canopy share does not fit into any specific geometrical category
(c) Trees of spreading habit –
Examples of trees of this type are:
Delonix regia (Gulmohar)
Lagerstroemia flosreginae (pride of India)
Pithecolobium saman (Rain Tree)
Though these trees vary greatly in size, their basic form is similar
(d) Trees of weeping habit –
Examples of trees of this type are:
Callistemon lanceolatus (Bottle brush)
Salix babylonica (Weeping willow / Peking willow).
The above classification is helpful in choosing various combinations of the above types to achieve desired function and visual objectives.
2. Soil Conditions
Physical as well as chemical properties of the available soil are important. These may or may not be amenable to change; they would therefore affect the choice of plant material considerably. Physical properties include consideration of light (for example sandy) and heavy (for example clayey) soils, and their structure. Chemical properties pertain to the presence or absence of nutrients and salts; soil, alkalinity, or acidity. An effective planting scheme.
3. Availability and Quality of Water
The water requirement may be derived from data on humidity and rainfall of plants’ natural habitat. The water table of the area where the plantation is to be done has a crucial bearing on the design of plants as well as a financial implication for reduced maintenance if planted appropriately.
4. Availability of Sunlight
The growth rate of plants is directly related to sunlight availability; such as plants that require (a) full sunlight, (b) partial sunlight, (c) predominantly shade, and (d) complete shade.
5. Quality of Air
Growth may be affected by chemical pollutants such as Sulphur dioxide or physical pollution such as dust. Certain plants have the ability to withstand pollution, such plants are imperative for industrial areas, roads, highways, etc.
6. Maintenance
The success of a designed landscape depends upon the growth of vegetation over an extended period of time; therefore, the maintenance of the landscape is also a design component.
7. Functional Aspects of Design with Plants
(a) Improve existing environmental conditions with respect to soil, drainage, microclimate, air pollution;
(b) Create a designed physical environment through the organization of open space; and
(c) Interpret and express the contemporary understanding of the man-nature relationship, that is, design with plants on an ecological rather than horticulture basis.
Shrubs
The functions are similar to those trees. Shrubs may be used together with trees to reinforce the functions, for example, noise barriers, shelter belts, enclosures, etc.
Other forms in which shrubs may be used are:
(a) Hedges: These require regular maintenance
(b) Shrubbery: Here plants are allowed to retain their natural shape; they therefore require little maintenance.
Shrubs provide barrier, which may either be visual or physical (hedges). Barriers may be required in a range of situations, for example, they may be only for defining space, or they may be required for security and have to be, therefore, necessarily impenetrable.
Groundcover
Groundcover plants are those which naturally grow to a very low height. Some of the uses for which they may be used are:
(a) Stabilization of soil on steep slopes such as embankments.
(b) As a low-maintenance substitute for grass (where the surface is not to be used).
(c) For providing variety in surface treatment.
(d) Contrast with paving materials, for example, to soften rigid lines of paving.
(e) As a subtle means of demarcating space, for example, in places where tall plants would be visually intrusive.
(f) In combination with other plants to provide contrast or harmony in form.
Climbers
Certain climbers because of their spreading habits may also be used as ground cover (for example Asparagus spp.) Climbers are useful for shading exposed walls from direct sunlight. They may also be used for stabilizing soil on embankments (for example, ficus stipulate, Ipomea biloba). On sites where a high degree of security makes fencing necessary, climbers and spreading plants like Bougainvillea species may be trained on boundary walls.
Planting for Shelter and Soil Conservation
The use of vegetation for controlling wind is widely recognized as an effective way of conserving soil and reducing erosion by wind. Vegetation may therefore be used for modifying the microclimate, by obstructing, guiding, deflecting or filtering wind current.
Vegetation areas designed to fulfill these general functions are usually classified as windbreakers and shelterbelts. Windbreaker is grown protective planting around gardens and orchards. Windbreakers generally consist of single or double rows of trees. Shelterbelt provides an extensive barrier of trees with several rows of trees. Plant species are chosen with particular regard to their physical and growth characteristics, and their effectiveness in achieving the desired results.
Function
Windbreakers and shelterbelts fulfill essential microclimatic functions in rural and urban environments. Benefits accruing from the plantation of shelter planting may be as follows:
(a) Reduction in wind velocity resulting in the arrest of movements of soil particles.
(b) Prevention of soil erosion.
(c) Modification of micro-climate; moderation of change in air temperature.
(d) Protection of crops from being blown by high winds.
(e) Reduction in evaporation of soil moisture. The increase in soil moisture content varies from 3 percent to 7.8 percent Water loss due to evaporation is lessened.
(f) Increase in soil moisture due to greater dew fall in sheltered areas has been found to be 200 percent higher than on exposed ground; heaviest dew fall is over a distance of 2 to 3 times the height of the shelterbelt.
(g) Beneficial effect on growth of plants that are affected by high winds.
(h) The zone of influence of shelterbelt on crop yield extends to a distance of 20 times the height of the belt, with the maximum effect being observed 10 times the height of the tree belt, on the leeward side.
Wind Erosion
Some of the basic functions of windbreaks and shelterbelts in arid and semi-arid areas are to conserve soil and reduce erosion by wind. The latter is a natural phenomenon in lands having very little rainfall (125 mm- 250 mm) and in areas adjoining a river, lake, or sea. Wind erosion is a serious problem in areas where the ground is virtually bare and devoid of vegetation.
Techniques for control of wind erosion
The principal method of reducing the surface velocity of wind, upon which depends the abrasive and transportation capacity of wind, is by vegetation measures.
(a) Porosity is important in the effectiveness of shelterbelts and proper selection of tree species is necessary. Porosity near ground level is desirable.
(b) Effectiveness of shelter planting depends more on height and permeability than on width. The width influences the general microclimate but above a certain minimum width, it does not affect the greater reduction in wind velocity.
Species suitable for windbreaks are
(a) For Dry and Arid Regions
(i) Acacia auriculiformis (Australian Blackwood)
(ii) Ailanthus excelsa (Maharukh)
(iii) Albizia lebbeck (Siris)
(iv) Azadirachta indica (Neem)
(v) Casuarina equisetifolia (Beef- wood)
(vi) Dalbergia sissoo (Sheesham)
(vii) Eugenia Jambolana (Jamun)
(viii) Grevillea robusta (Silver oak)
(ix) Peltophorum ferrugineum (Cooper pod)
(x) Tamarindus indica (Imli)
(xi) Pongamia glabra (Indian beech)
For Coastal Area
(i) Anacardium occidentale (Cashew)
(ii) Ailanthus malabarica (Alston)
(iii) Cassuarina equisetifolia (Beef-wood)
(iv) Pongamia glabra (India beech)
(v) Sesbania aculeate (Sesban)
(vi) Thevetia Peruviana (Yellow oleander)
(vii) Thespesia populnea (Indian Tulip)
(viii) Vitex negundo (Sephali)
Air Pollution Control by Plants
Air pollution may be caused by areas or point sources such as cities, industrial areas, factories or by linear sources such as highways. Vegetation buffers can minimize the build-up of pollution levels in urban areas, by acting as pollution sinks.
Effect of Plants
Plant leaves function as efficient gas exchange systems. Their internal structure allows rapid diffusion of water-soluble gases. These characteristics allow the plant to respire and photosynthesize, and they can also remove pollution from the air. Some of the beneficial results of plantations may be:
(a) They are good absorbers of Sulphur dioxide.
(b) Parks with trees have an SO2 level lower than city streets.
(c) Roadside hedges can reduce traffic-generated airborne lead, on the leeward side.
(d) Heavy roadside planting in the form of shelterbelts can result in a reduction in airborne lead.
(e) Complete dust interception can be achieved by a 30m belt of trees. Even a single row of trees may bring about a 25% reduction in airborne particulate.
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SOURCE – NBC VOL 2016