Lesson 5 How to Choose Suitable Trees
Selecting the right tree for a particular place can avoid costly disappointments later .It is important in landscape plants .How to select trees ?There are some basic considerations that we need before we plant trees .
1. 1.Site Evaluation
The first consideration is about the site conditions. It is important to keep in mind that
no two sites are exactly alike; various conditions both above and below the ground
affect the success of a particular tree species .It is important to consider both above
–ground and below-ground site attributes during site evaluation .So we should know
site evaluation is the first step in selecting proper trees for a planting site.
About site evaluation ‘s above –ground evaluation ,many elements should be taken into
account .Environment factors such as light and slope exposure ,wind ,salt and existing
tree presence should be considered ,as well as urban conditions such as overhead
wires ,street and security lights ,buildings signs vandalism and regulation .Important soil
attributes that affect tree selection are pH, drainage ,depth salinity ,distance to the
water table , and obstacles to root growth such as curbs. Many plantings fail because
these factors are make provisions to remove and stockpile it . Good soil is precious
and should not be wasted .It can be brought back to the site once the job is complete
to promote tree growth.
2. 2.Potential Site Modifications
After the site evaluation ,we should think about the potential site modifications .
Modifications made to the site can help accommodate a wider variety of tree
species .When made before planting ,site modifications such as moving wires or street
lights ,grading ,improving drainage ,and incorporating soil amendments over broad
areas can have an impact on sail conditions that will affect tree growth and species
3. 3.Evaluate Maintenance Practices
Understanding how the site will be managed after planting is a critical factor in tree
selection . Maintenance issues such as irrigation , pruning , fertilization ,and pest control
can affect whether a tree is able to thrive .For example ,if a planner knows that trees will
not receive any pruning once they are in the landscape ,then a tree with a naturally
good structure is preferred .
4. 4.Choosing Desirable Tree Attributes
Next consideration is about the desirable tree attributes .Up to this point in the
evaluation process , tree have been chosen primarily for their ability to grow at the site.
While this is the most crucial criterion for tree selection ,desired tree attributes such as
function ,size ,form, and longevity are also important when choosing a species.
Healthy trees provide us with many benefits .They give shade , produce oxygen ,control erosion ,protect our water resources ,increase asphalt durability ,support wildlife ,and stabilize stream banks .The function we would like a tree to provide may dictate its size ,shape(form),life span ,canopy density ,color ,growth rate ,fruit characteristics and other attributes .
Large tree (>50 ft at mature height ) are the obvious choice for providing shade to large open spaces and for planting along streets if there is proper space above and below ground . Medium or large trees will cast the most shade onto a building ,which can reduce air conditioning bills when the trees are placed properly .Small trees (<30 ft at mature height) are often suggested or planting downtown areas where soil space is limited ,but they provide little shade .Small or medium –sized trees may be good
choices for planting near a deck or patio ,or in areas exposed to potential hurricane-force winds .
Tree form can have a big impact on tree requirements .Small ,spreading trees that are multi-trunked require regular pruning if they are planted too close to a sidewalk ,whereas a small ,upright tree or a larger tree can be rained to grow over the walk or street .Trees with a pyramidal form usually requires less pruning to develop strong ,wind-resistant branch structure than those with other forms . Trees with rounded ,oval or spreading canopies often need periodic pruning in the first 25 years after planting to ensure good structure and to provide clearance .
It would appear that large ,long –lived trees might be the logical choice fir planting in most landscape situation ,since they would provide for a lasting effect .However ,with reasonable placement and care ,long-lived trees will probably outlast many of today ‘s streets ,homes , and buildings .Many structures are renovated or expanded 30-50 years after construction . The renovation is often so extensive root system in order to keep the tree alive. For this reason ,concern about tree longevity may be less important in highly urbanized landscape unless special provisions are undertaken to protect the tree.
Basic Ecological Principles
In the specific selection of plant material ,it is important to remember the following : Select a species that is adaptable to the site environment ;
Select a species that can be easily removed after other plants have been established ; Avoid species that are subject to disease or damage from serve climate change ; Use a plant type that will intercept and check the movements of water or sand across the site.
Basic Biological Principles
Basic biological principles about desirable tree attributes maybe should be mentioned especially from a design viewpoint rather than from a horticultural viewpoint .They are :
The anticipated size of the tree at various ages –say 5 years after painting ,10 years after
planting ,and at early maturity – as well as the effective life of the plant .
Deciduous or evergreen(coniferous or broadleaved);
Appearance and character of trees as related to trunk ,branch and twig structure ,and back ;
Density of shade;
The foliage color in spring ,summer and fall ,and the relative leaf-out and leaf-from times ;
Relative time of following ,duration of period of blood ,and flower color of plants used in floral displays ;
Fruit color ,duration ,and possible hazard or nuisance from tree fruits .
Other considerations should be taken into account are: Laws and regulations ;Time considerations ;Economic ability.
5.Laws and regulations
On the national level , some laws and regulations ,for example, the USA Endangered Species Act , many control the collection of seeds or the propagation of plants on the endangered list .Local ,state ,or even regional restrictions may prohibit the use of certain situations. Many municipal governments may restrict the height of grasses used as a lawn or groundcover mass.
Time must be budgeted to grow or collect the desired items .Some species must be
dormant for specific periods of time before germination is attempted .Topsoil may
need to be place days or even months before formal planning operations begin .If a
“natural planting “process is the intent of the project ,both the client and designer must
be prepared to invest a great amount of time to reach their objective . 7.Economic Ability
One of the major goals of most landscape project id to develop as much area of the site as possible with the minimum amount of investment .
Tree selection may require more work and creativity to find the right tree ,but it is well worth the effort . Following these considerations can help us to select the right trees.