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
 
 

        B. Palm / Fern  Model

                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

  V. Tree architectural Model

        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)