WHAT IS A TREE?
I. Practical
Definition
A. Woody Plant
B. >= 4 meters (13 ft) at maturity
C. Single Trunk at least 7.5 cm (3 inches) in diameter that is unbranched for at least a meter
D. More or less definite
crown
II. Botanical tree is composed of:
A. Roots (R)
B. Trunk (T)
C. Crown (C)
III. Four basic ways in which trees develop
A. Pipe Model (Angiosperm,
Gymnosperm)
C,T,R develop synchronously
C,R develop first, then T
C. Bamboo Model
Like Palm, but with subterranean branches
producing many T's
D. Epiphytic Model (Strangler Fig)
C,R develop in epiphytic position,
T represents transformed wood R's
IV. Tree architecture
Morphological expression
of the genetic blueprint at any one time
The growth program which determines the successive
architectural phases
A. Often difficult
to recognize models because of the
need for observations from seedling to flowering
maturity
B. Some important features
of models:
1. Branched vs Unbranched
2. Continuous vs Rhythmic Shoot Extension
3. Orthotropic vs Plagiotropic Branch Differentiation
4. Time of Branch Outgrowth
a. Syllepsis = immediate development
b. Prolepsis=period of dormancy
5. Terminal vs Lateral Flower Position
VI. Halle' and Oldeman reduced all tree forms to 23 Models!.
A. Neutral System of Labeling
1. No phylogenetic connotations
2. No type species
B. Applications and Implications
1. Describes trees in Developmental Framework
2. Generates useful generalizations related to
functional significance of tree form
a. Greatest variety of tree form in tropics
b. No necessary correlation between architecture
and broad systematic position
3. Reveals previously unappreciated correlations between modes of branching and chronology
of development:
Most Introductor Texts Describe Tree Form
Columnar
Excurrent
Decurrent
(Deliquescent)
Strong Apical Weak Apical
Dominance? Dominance?
REVERSE MAY BE TRUE !
Excurrent Form: Weak apical dominance, but Strong Apical Control
=Apex always exhibits a partial inhibition on growth of lateral branches
Decurrent Form: Strong apical dominace, but Weak Apical Control
=Apex completely inhibits lateral buds the first year, but looses control in
subsequent years
4. Generates insights into how most trees repair damaged crowns via the
" Reiterative Complex" = following crown damage the
architectural model is repeated to repair damage
a. via dormant buds
b. via branch reorientation
C. Crown Shape is determined
by
1. Architecture (deterministic)
2. Reiteration (opportunistic)
events experienced throughout a trees life
D. Computer
simulation of architectural models can reveal much information in relatively short time periods.
E. Relationship between form
and function has practical
importance
Structural basis for hydraulic architecture is important
to understanding
disease
and responses to environmental stresses
VII. Maturation (Phase Change in Trees
A. Relatively rapid and predictable
changes characteristic of
transition from juvenility to adulthood
1. Length of junenile stage varies considerably
< 1 year
for entire life (oranamental forms)
2. Adulthood = age of first flower formation
B. Distinct from Aging =
gradual reduction in growth rates of
vegetative and reproductive tissue (vigor),
decrease in
metabolism, heartwood formation as tree gradually increases in size and complexity.
VIII. Some morphological characteristics associated with phase change
A. Form of Leaves
1. Lobed, Toothed -> Entire
2. Horizontal -> Pendant Orientabion
3. Stomata on lower side -> Stomata on both sides
4. Broad -> Narrower
B. Leaf Retention
1. Abscision occurs later in year for juvenile
C. Thorniness
1. Thorns (modified pointed stems) -> No thorns
D. Formation of Anthocyanins
1. Young leaves Reddish -> Young leaves Green
E. Rooting of cuttings
1. Easy -> Difficult to impossible
F. Often more basal branches
retain juvenile characteristics while more apical branches
have adult characteristics
G. May or may not be stable during vegetative propagation
IX. Attempts to Control Phase Change
A. Biological Interest
B. Practical Interest
1. Breeding programs
2. Fruit set
3. Propagation
C. Acceleration of maturation
1. Controlled Photoperiod
2. Exogenous Gibberellic Acid (GA)
D. Reversion to juvenility
1. Heavy pruning
2. Grafts of adult scions onto juvinile stocks
3. Exogenous Gibberellic Acid (GA)