Biology of Trees and Shrubs

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Biology of Trees(and Shrubs)

• Barb Larson
• Horticulture Educator
• Kenosha County

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What is a Tree?

• Trees tallest plants in ecosystem because of
  woody tissue gives height and therefore more
  accessible to light
  
• Woody plant
• Stem increases in diameter every year
• Palms not true trees

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Definitions

• Tree erect woody plant with one central trunk
  ( 25 feet)

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Definitions

• Shrub erect woody plant with numerous woody
  stems (

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Definition

• Vine woody plant requiring a support to be
  upright
  

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What happens to make a woody plant a tree or
shrub?

• Botany Refresher
• Meristem area of rapidly dividing cells
• Apical (terminal) meristem - tips
• Axillary (lateral) meristem side buds
• Cambium - stems
• Adventitious meristem

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Tree vs. ShrubIts in the Hormones

• Apical buds/axillary buds
• Apical control (persistence of central leader)
• Apical dominance (apical bud prevents side
  shoots
  

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Shrub Form

• Poor apical control
• Poor apical dominance

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Tree Form

• Tree with strong central leader and reduced side
  branching
  
• Strong apical control
• Strong apical dominance

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Tree Form

• Poor apical dominance
• Strong apical control
• Highly branched
• Excurrent growth habit

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Tree Form

• Strong apical dominance
• No central leader
• Poor apical control
• Minimal branching in crown
• Decurrent growth habit

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WoodA Tale of Two Cambiums

• Secondary growth in stem and root (wood)
• Increase in diameter
• Two meristems or cambiums
• Vascular cambium thin layer of cells
• Xylem
• Phloem
• Cork cambium

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Vascular Cambium

• Cambium meristem produces
• Xylem
• Water conduction (roots to shoots)
• Tracheads and vessel elements
• Phloem
• Transports organic compounds (sugars) and some
  minerals (N, P,) to high use areas
  
• Sieve tubes and companion cells

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Vascular Cambium
Vascular Cambium
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Stems - Cross Section
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University Arkansas-LittleRock
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Xylem

• Cells die
• forming long ( 1 meter) tubes
• Water moves thru tubes

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Tree Rings Seasonal Growth

• Growth rate/vessel size
• Spring/early wood
• Summer/late wood

Diagram pbs.org
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Tree Rings

• Cambium active only in growing season
• Ring number age
• Ring thickness growing conditions

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Sapwood Heartwood

• Sapwood
• Outer 1-10 rings water transport
• Other vessels open but not used
• Heartwood vessels blocked by colored gums

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Phloem

• Movement of photosynthetic products any
  direction
  
• Sinks growth, storage, seeds, fruits, wounds
• Only current season growth functional
• Older phloem rings crushed by expanding xylem

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Cork Cambium (Phellogen)

• 1st year stem epidermis like herbaceous
• Xylem grow stretches and breaks epidermis
• Cells right under epidermis form cork cambium

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Cork Cambium (Phellogen)

• Produces cork cells
• Growth of trunk causes repeated breaking of old
  cork cambium and production of new cork cambium
  
• Cork cambium replaceable if damaged (not vascular
  cambium)

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Bark Characteristics

• Distinctive patterns develop from one or more
  layers cork cambium and cork
  
• Continuous ring or patches
• Protects against weather, insects, diseases,
  animals

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Water Movement

• How does water get 367 feet up to the top of a
  Coast Redwood tree?

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Transpiration

• Transpiration
• Decreased in dense stands
• 2-4 times less water loss than solitary tree
• Photosynthesis rate lower than herbaceous

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Cohesion-tension theory

• Open pipe (works for 30 ft) very thin tube with
  high attraction to water
  
• Water molecules stick to each other creating
  continuous column of water
  
• Hot sunny days breaks in water column
  (cavitation) broadleaves larger vessels more
  water flow but greater cavitation conifer
  smaller vessels with less cavitation more drought
  tolerant

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Surviving the Seasons
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Fall Color

• Beginning of winter dormancy and hardening brings
  leaf senescence
  
• Nutrients in leaves broken down
• 60 of nitrogen recovered (chlorophyll)
• Yellow, brown compounds visible
• Reds synthesized from remaining carbohydrates
• Leaf drop
• Abscission zone in petiole

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Winter Dormancy

• Apical meristem and cambium activity stops poor
  growing conditions
  
• Triggered by shorter daylength
• Dormancy
• Require several weeks of cold before regrowth can
  occur (chilling requirement)
  
• Increase in day length to release bud dormancy

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Winter Hardening

• Ability to withstand very cold temperatures
• Progressive process (stimulated by short days and
  
• Ice formation in bud cells reduced by
• Increased solutes
• Decreased water (desiccation)
• Process reverses in spring

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Tree Roots in Winter

• Remain active after top is dormant
• After soil temp gets below certain level will
  become dormant but not to the extent of top
  
• Less tolerant of cold than top
• Rule of Thumb one hardiness zone less

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Spring

• Water
• Sugar moves from rays to xylem
• Sugar draws water by osmosis from surrounding
  cells
  
• Maple sugaring

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Spring

• Spring flowering
• Flower buds formed previous summer
• Dormant until chilling or day length requirements
  met
  
• Many temperate tree seeds require cold moist
  conditions (stratification) prior to germination
  

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Buds, Stems, Roots
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Stem External Features
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Stem External Features

• Nodes
• Where leaf attached
• Internodes
• Space between nodes

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Leaf/Bud Arrangement

• Alternate Opposite Whorled

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Stem Features-Buds

• Undeveloped shoot (apical meristem)
• Functional bud types
• Vegetative bud - leaves and stem
• Flower bud flowers
• Mixed bud leaves, stems, flowers

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Stem Features Bud Scales

• Cover and protect terminal and lateral buds

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Stem Features Bud Scale Scars

• Wrinkles or rough spots from bud scales

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Tree Growth and Bud Scale Scars
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Stem Features Leaf Scar

• Scar left from leaf after drops
• Vascular bundles scars
• one or more dot-like scars
• Bundle scars pattern and leaf scar shape used for
  ID

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Stem Features - Lenticles

• Corky outgrowths
• Used for gas exchange

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Root Spread
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Mycorhizzea

• Associated with roots of woody plants
• Function like hair roots absorb water and
  nutients
  
• Most mycorhizea on outside of root
• Exception maples, ericaceous plants, sweet gum,
  tuliptree
  
• Root nodules alder, legumes (black locust)

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Geotropism in Trees

• Positive geotropism roots downward (towards
  gravity)
  
• Negative geotropism stems upward (away from
  gravity)
  
• Plagiotropism stems and roots laterally or
  horizontal (perpendicular to gravity)
  
• Propagation issues -

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Juvenile Adult Phases
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Thank you!

• Questions?

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References/Sources/Images

• Michael Knee, The Ohio State University
• University of Florida Extension
• University of Illinois Chicago
• University of Wisconsin-Madison, Botany Dept.