ISA Arborist Certification Training - Chapter 1

ISA Arborist Certification Training - Chapter 1 - Tree Biology

• Tree Biology Defined: The study of tree structure, function of those structures, and the interrelationship between them.

What is a Tree?

• Long-lived perennial: Trees are long-lasting.
• Woody: Trees have a woody structure.
• Compartmentalizing organism: Trees have a compartmentalized structure.

Types of Trees

• Deciduous: Trees that lose their leaves (oaks, maples, ash)
• Deciduous Conifer: A type of deciduous tree with cone-like structures (larch, bald cypress)
• Coniferous: Trees that keep their leaves year-round (pines, spruces, firs, junipers, yews)

Tree Form

• Excurrent Trees:
  • Strong central lead
  • Most young trees
  • Conifers, sweet gum
• Decurrent Trees:
  • Lateral shoots outgrow original terminal shoot
  • Round-headed tree
  • Typical of mature trees
  • Oaks, elms

Plant Growth - Cellular Level

• Cell growth:
  • Mitosis: cell division
  • Cell differentiation:
    • Cells change structure to specific function
    • Tissues arranged into organs: roots, stems, leaves, flowers, fruit
    • Organs function as an organism (tree)

Tree Growth

• Cells & Tissues (GROWTH):
  • Meristems: Cells that produce other cells
  • Differentiation: Change in cell structure for needed function
  • Apical meristems: Meristems at shoot/bud and root ends (primary growth)
  • Cambium: Lateral meristems producing the tree's vascular system (secondary growth)
  • Cork Cambium: Lateral meristem that produces bark

Tree Growth - Primary Meristem

• Responsible for elongation of roots and stems.
• Located in the tips of roots and stems (buds).

Tree Growth - Secondary or Lateral Meristem

• Increases the diameter of the tree.
• Vascular cambium: Produces xylem or phloem.
• Cork cambium: Produces bark.

Growth Tissue: Cambium

• Location of growth.
• Produces: Phloem (outside), Xylem (inside).

Tree Anatomy Vocabulary

• Cambium: Produces xylem and phloem.
• Xylem: Produced inside cambium, the wood of the tree. Moves water and minerals to leaves, supports tree & stores sugars.
• Phloem: Produced outside cambium. Moves sugars down from the leaves.

Tree Anatomy

• Heartwood: Non-water conduction, non-living xylem.
• Sapwood: Water conduction, living xylem.
• Cambium: Thin layer of active xylem & phloem.
• Bark: Outer covering.

Vascular Tissue - Xylem

• Xylem is the wood of trees
• Functions:
  • Conduction of water & dissolved minerals
  • Support weight of tree
  • Storage of carbohydrates
  • Defense against disease & decay

Vascular Tissue - Xylem (Composition)

• Composed of dead and living cells:
  • Tracheids: Water conduction & support.
  • Fibers: Mechanical strength
  • Parenchyma cells: Maintain water balance & store carbohydrates
  • Vessels: Hardwood trees

Vascular Tissue - Xylem (Water Transportation)

• Transportation of water and minerals occurs via transpiration (loss of water through leaves)
• Water molecules are pulled in long, hydrogen-bonded chains from root to leaf.
• Conduction in sapwood; conifers - 2-12 rings; hardwoods - outermost rings especially elm.
• Non-water conduction occurs in heartwood.

Vascular Tissue: Phloem

• Food transport
• Living cells:
  • Sieve cells (conifers)
  • Sieve tube cells
  • Companion cells
  • Parenchyma cells

Vascular Tissue - Phloem (Translocation)

• Translocation: conduction of sugars produced in leaves to other parts of the plant.
• Photosynthate moves from source to sink (plant parts that use more energy than they produce).
• Axial transport: materials flow up and down.
• Radial Transport: Parenchyma cells that extend across (radial) xylem and phloem (transport sugars, store starch, restrict decay.)

Bark

• Function:
  • Moderates interior temperature
  • Reduces water loss
  • Protects against injury
• Composition:
  • Nonfunctional phloem & corky tissues
  • Contains wax & oil to minimize water loss
• Lenticels: Small openings for gas exchange.

Tree Organs

• Leaves
• Stems
• Roots
• Flowers
• Fruits

Leaves - Primary Purpose

• Photosynthesis:
  • Inputs: Carbon dioxide, Water, Light
  • Outputs: Carbohydrates/sugar, Oxygen

Leaves - Stomata

• Control loss of water vapor (transpiration)
• Control gas exchange.
• Guard cells controlled by light, temperature, wind and humidity - open during day, close at night

Leaves - Deciduous Trees

• Leaves lost due to cell changes/growth regulators (abscission zone)
• Enables leaf drop in fall
• Protects against desiccation (drying) and pathogen (disease agent) entry

Modified Leaves

• Arid regions have:
  • Thick cuticle
  • Leathery leaves
  • Few stomata
• Succulents have:
  • Water-retaining leaves
  • Dense hairy coverings

Tree Parts - Stems

• Strongly attached underneath, weakly attached above.
• Branch collar: Tissue bulge around branch base (autonomous – function independently)

Tree Parts - Stem Anatomy

• Node: Gives rise to leaves & buds.
• Internode: Distance between nodes.
• Terminal bud: Primary growth.
• Terminal bud scale scar: Start of new growth of current year.

Tree Parts - Buds

• Terminal/apical buds: Located at the end of a shoot.
• Lateral/axillary buds: Located on the sides of the stem.
• Adventitious buds: Arise from loss of primary bud.
• Epicormic shoots: Dormant buds that sprout and grow.

Tree Parts - Roots

• Main Functions:
  • Anchorage
  • Storage
  • Absorption
  • Conduction
• Roots need water & air for optimal growth
  • Absorbing roots: Small, fibrous organs growing at the end, in the top foot of soil.
  • Lateral/horizontal roots: Near the surface.
  • Sinkers roots: Grow vertically downward from lateral roots, found within a few feet of the trunk.
  • Most roots are found in the upper 1-12” of soil.
  • Taproot: Downward growing root in young trees.
  • Root extent and directional growth depend on environment, not genetics.
  • Mycorrhizae: Symbiotic relationship of roots with fungi
  • Symbiosis: Both organisms benefit from the arrangement
    • Fungi get food in return for aid in absorption of water and minerals.
  • Water enters young roots via osmosis.

Tree Parts - Roots (Osmosis)

• Water enters young roots or mycorrhizal roots via osmosis.
• Osmosis requires fluid transport from higher concentration to lower concentration.
• Reverse Osmosis: Water movement from out of the roots into soil (example: de-icing roads with salt).

Allelopathy

• Production and release of chemical substances by one species that inhibit the growth of other plant species.

Flowers & Fruit

• Flower: Reproductive structure of the plant.
• Once pollinated, give rise to the fruit or seed.

Tree Physiology - Photosynthesis

• Process converting light into sugar and starches.
• Chlorophyll is the green/leaf pigment that absorbs sunlight, stored in chloroplast cells of leaves.
• Raw materials: Carbon dioxide, Water

Tree Physiology - Respiration

• Energy made from photosynthesis is used.
• Oxygen is needed
• Carbon dioxide and water are given off
• Trees must survive flooded rootsand defoliated leaves by caterpillars.

Tree Physiology - Transpiration

• Water loss through stomata.
• Helps cool leaf during hot times and aids water uptake in xylem.
• Dependent on water, temperature, and humidity
• 90% of absorbed water is lost in leaves.

Tree Physiology – Control of Growth and Development

• Plant growth limited by genetics and environment
• Plant hormones:
  • Auxin: Produced in shoots, alters crown growth, involved in tropisms
  • Cytokinin: Produced in roots, shoot initiation and growth
• Hormones signal:
  • Cell division
  • Cell elongation
  • Flowering
  • Fruit ripening
  • Leaf drop
  • Dormancy
  • Root development
• Tropisms:
  • Geotropism: Gravity response
  • Phototropism: Light response

Tree Physiology - Compartmentalization

• CODIT (Compartmentalization Of Decay In Trees): A system of defense.
• Three walls resist decay:
  • Wall 1: Resists vertical spread, plugs up xylem
  • Wall 2: Resists inward spread, plugs latewood cells
  • Wall 3: Inhibits lateral spread, activates rays cells to resist decay
  • Wall 4: The strongest wall to form after injury to protect from outward decay (Barrier zone).

Palms

• Monocot
• Have no cambium layer
• Have no growth ring of xylem
• Have vascular bundles of xylem & phloem

Explore the fundamentals of tree biology in this quiz, which covers the structure and function of trees, their types, and growth patterns. You will learn about deciduous and coniferous trees, as well as the distinctions between excurrent and decurrent forms. This is essential knowledge for aspiring arborists.