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- A true tree is a
perennial
woody plant of considerable
size (generally at least 5- 6 m high at
maturity), having a single main
erect trunk with side
branches and usually a distinct
crown.
- The term tree is also used to indicate
plant or shrub resembling a
tree in form or size, a large shrub or a
nonwoody plant that
resembles a tree, for example, a palm tree or tree fern.
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Compared with most other forms of plants, trees are long-lived. A few
species of trees grow to 100 m tall, and some can live for several
millennia. A plant form that is similar to a tree, but generally having
smaller, multiple trunks and branches that arise near the ground, is
called a shrub. However, no clear-cut
differentiation between shrubs and trees is possible.
The component parts of a tree are the
roots, trunk and
crown (branches,
twigs and
leaves) The
underground roots of a tree are
generally fixed in earth, provide anchorage and absorb water and
nutrients from the soil. Above ground, the trunk gives height to the
leaf-bearing branches. Not all trees have all the plant
organs mentioned above. For examples:
Most palm trees are not branched, the saguaro
cactus has no functional leaves,
tree ferns do not have bark, etc.
Most species of trees today belongs to the
flowering plants and
conifers while
the earliest species of trees were tree ferns, cycads, ginkgos and
horsetails. Trees may be broadly grouped into exogenous and endogenous
trees according to the way in which their
stem diameter grows. Exogenous
trees, which comprise the great majority of modern trees (all
conifers, and
all broadleaf trees), grow
by the addition of new wood
outwards, immediately under the bark.
Endogenous trees, mainly in the
monocotyledons (e.g. palms), grow by addition of new material
inwards.
Most species of trees today belongs to the
flowering plants and
conifers while
the earliest species of trees were tree ferns, cycads, ginkgos and
horsetails.
Trees are important components of the natural
landscape and significant
elements in landscaping. A landscape covered by a large area of trees is
called a forest. |
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